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Aluna Everitt

A Novel Approach to Interface Fabrication

Using Laser Cut Optically Clear Perspex

B.Sc. (Hons) Information Technology

for Creative Industries

20/03/2015

Aluna Everitt SCC.300 2015

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“I certify that the material contained in this dissertation is my own work and does not

contain unreferenced or unacknowledged material. I also warrant that the above statement

applies to the implementation of the project and all associated documentation. Regarding

the electronically submitted version of this submitted work, I consent to this being stored

electronically and copied for assessment purposes, including the Department’s use of

plagiarism detection systems in order to check the integrity of assessed work.

I agree to my dissertation being placed in the public domain, with my name explicitly

included as the author of the work.”

Date:

Signed:


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ABSTRACT

Increasingly digital fabrication technologies are being adopted in a wide range of settings as

they allow users to rapidly and accurately produce physical designs. Of these technologies,

laser cutters are particularly interesting as they are able to work with a wide range of

materials. This report explores the ways in which the optical properties of clear Perspex

material can be exploited in order to add interactive and visual display capabilities to static

objects. This has potential to support the creation of a new range of wearable technologies,

enclosures, and other designs that do not require expensive and generic circuitry and

electronics. To achieve this, an exploration of material properties was conducted to devise

novel approaches of producing interactive visual displays using a laser cutter. From this,

three fundamental interface elements are produced (i.e. a button, an accelerometer, and a

seven-segment display) and combined into a wearable watch prototype. Finally, a discussion

of design guidelines is presented.


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TABLE OF CONTENTS

1. Introduction .......................................................................................................................... 8

1.1 Research Question ............................................................................................................ 8

1.2 Exploring Design Space ................................................................................................... 8

1.3 Outline of Report .............................................................................................................. 9

2. Background ........................................................................................................................ 10

2.1 Related Work .................................................................................................................. 10

2.2 Summary ........................................................................................................................ 13

3. Material Exploration ......................................................................................................... 14

3.1 Visual Exploration .......................................................................................................... 14

3.1.1 Distance Study ......................................................................................................... 14

3.1.2 Angle Study ............................................................................................................. 16

3.2 Interactive Exploration ................................................................................................... 19

3.2.1 Touch Study 1 .......................................................................................................... 19

3.2.2 Touch Study 2 .......................................................................................................... 22

3.2.3 Touch Study 3 .......................................................................................................... 24

3.3 Discussion and Summary ............................................................................................... 25

4. Prototype Elements ............................................................................................................ 26

4.1 Interactive Application Elements ................................................................................... 26

4.1.1 Button ...................................................................................................................... 26

4.1.2 Accelerometer .......................................................................................................... 28

4.2 Interface Application Elements ...................................................................................... 31

4.2.1 Initial Seven-Segment Display (LEDs Around 4 Sides) ......................................... 31

4.2.2 Initial Lighting Observations ................................................................................... 32

4.2.3 Refined Seven-Segment Display (LEDs on Bottom) .............................................. 35


5. Application - Watch Prototype ......................................................................................... 38

5.1 LED Enclosure ............................................................................................................... 38

5.2 Interface .......................................................................................................................... 39

5.3 Interactive Button ........................................................................................................... 43

5.4 Final Integration ............................................................................................................. 44



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6. Design Considerations and Discussion ............................................................................. 47

6.1 Apparatus ....................................................................................................................... 47

6.2 Design and Fabrication of Enclosure ............................................................................. 47

6.3 Design and Fabrication of Display ................................................................................. 48

6.4 Programme Display ........................................................................................................ 49

6.5 Programme Interactive Element ..................................................................................... 50


7. Conclusion .......................................................................................................................... 52

7.1 Review of Aims .............................................................................................................. 52

7.2 Limitations ..................................................................................................................... 52

7.3 Future work .................................................................................................................... 53

7.4 Learning Outcomes ........................................................................................................ 53

Bibliography ........................................................................................................................... 54

Appendices .............................................................................................................................. 55

Prototype Elements .............................................................................................................. 55

Seven-Segment Display Chapter .......................................................................................... 56

Watch Chapter ...................................................................................................................... 59

Project Proposal .................................................................................................................... 60

Working Documents Link: http://www.lancaster.ac.uk/ug/everitta

Report Word Count: 13,648

http://www.lancaster.ac.uk/ug/everitta


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TABLE OF FIGURES

Figure 2.1: Device fabricated through Printed Optics [left]. Device with curved display

produced through PAPILLON [right]………………………………………..………………10

Figure 2.2: 3D printed device fabricated through Savage’s algorithmic process of subtraction

to accommodate manually embedded active components………………………...…………11

Figure 2.3: Ficon tangible 3D display devices with interactive touch capabilities through

table top systems……………………………………………………………………………..12

Figure 3.1: The hardware used in the LDR distance experiment. Black plastic used on LDR

so no light reflects…………………………………………………………………………....15

Figure 3.2: This graph shows the strong negative correlation between the means of the two

variables: light intensity and material length…………………………………………..…….16

Figure 3.3: Arduino, LED and LRD circuit mount for angle study…………………………17

Figure 3.4: This line graph shows the means of expected light intensity readings (based on

the distance formula) and actual light intensity readings for every 10° variation in the

material…………………………………………………………………………………….....18

Figure 3.5: The edges and corner of the material are illuminated brighter than the

surface…………………………………………………………………………………..……18

Figure 3.6: Imperfections can be seen on the laser cut edge of the material - under 30 x

magnifications………………………………………………………………………………..18

Figure 3.7: Arduino, LED and LRD circuit mount for touch study. Finger is applied at 20mm

where the LDR is positioned. Then touch is applied every 20mm along the surface until

120mm distance is reached. No touch is applied at 0mm distance…………….…………….20

Figure 3.8: This line graph shows the average light intensity from the bottom of the material

when touch is applied. Touch distance 0mm represents that no touch is applied and touch

distance 20mm represents when touch is applied directly above the LDR sensor……...……20

Figure 3.9: Volume control device concept using a strip of clear material, an LED light

source, and an LDR sensor……………………………………………………………….…..21

Figure 3.10: Arduino, LED and LRD circuit mount for touch study 2…………………...…22

Figure 3.11: Average light intensity from the first data sample collected. This shows an

irregular pattern that was not expected………………………………………………….……23

Figure 3.12: Line graph visualising the average light intensity from the second data sample

collected. This shows even more irregularity that was not expected…………………….…..23

Figure 3.13: Light intensity decreases as the number of fingers on the surface of the material

increases………………………………………………………………………………...……24

Figure 4.1: Button light switch when no interaction occurs…………………………...……27


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Figure 4.2: As pressure on the surface of the material increase LED 2 changes colour from

yellow to pink…………………………………………………………………………….…..28

Figure 4.3: Accelerometer prototype (top not present) with LED and LDR situated

opposite sides of rectangular enclosure………………………………………………………30

Figure 4.4: Comparison of vertical and horizontal displacement based on light intensity….30

Figure 4.5: SSD enclosure (85x120mm) consisting of three layers with LEDs positioned on

all four sides………………………………………………………………………………….31

Figure 4.6: Test 1 with five active LEDs illuminates all of the seven segments and visualises

light path from LED sources proficiently on matt etches…………………………………....32

Figure 4.7: Criss cross pattern etches distribute light rays more consistently compared to flat

matt etches……………………………………………………………………………………33

Figure 4.8: Cuts from test 9 enhances illumination of five segments………………….……33

Figure 4.9: Design and applied SSD with black material insert that isolates each segment of

the display...…………………………………………………………………………….……34

Figure 4.10: SSD displaying digits from 0 to 9 in a range of colours in full ambient

light…………………………………………………………………………………………...34

Figure 4.11: Two layer SSD with LEDs only at the bottom of the enclosure……………….35

Figure 4.12: Single layer SSD design with black inserts and final implementation of an SSD

displaying the figure “4”……………………………………………………………………..36

Figure 4.13: Printed Optics numeric display (a) consisting of embedded air pockets that

reflect light when illuminated (b). The numeric display fabricated through laser cutting (c) in

contrast only uses one layer of material to visualise figures 0-9……………………………..37

Figure 5.1: LED enclosure for watch prototype with chain of seven LEDs situated

inside…………………………………………………………………………………………38

Figure 5.2: Refined display for interactive watch prototype. Consisting of optically clear

Perspex (depth 5mm) and corresponding black material partitions (width:

0.72mm)………………………………………………………………………………...……39

Figure 5.3: Initial watch interface (secured with adhesive to ensure robustness) inserted into

LED enclosure………………………………………………………………………………..40

Figure 5.4: Due to angle restrictions the initial design of the display did not allow light to be

transmitted efficiently to the top sections as shown by numerals 6 and 9…………………...41

Figure 5.5: Refined design of the display enhanced illumination of both figures regardless of

light or dark background and the addition of fascia………………………………………….42

Figure 5.6: Button actuation device consisting of one LED, one LDR, and a strip of optically

clear material…………………………………………………………………………………43

Figure 5.7: Figures 0 to 9 displayed on final watch prototype in full ambient light. The

middle section is no as well illuminated compared the surrounding sections………………..44


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Figure 5.8: Figures 0 to 9 displayed with no ambient light present. Each figure is visualised

with greater clarity though the middle segment is still less obvious…………………………44

Figure 5.9: Watch used when no ambient light is present compared to when ambient light is

present……………………………………………………………………………………..…45

Figure 6.1: To display numeric figure “3” LEDs 3, 4, 5, 6, and 7 must be active whilst LEDs

1 and 2 must be inactive…………………………………………………………………..….49

Figure 6.2: Example Arduino processing code for visualising numeric figure “3”……..…..49

Figure 6.3: Word cloud of key phrases and words taken from observations conducting during

open day demonstrations……………………………………………………………….…….51

Figure 7.1: Voronoi diagram isolating each of the eight points with maximum space around

each centre……………………………………………………………………………………53


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1. INTRODUCTION

1.1 RESEARCH QUESTION The majority of interactive interfaces use electronic components situated underneath the

surface of a display (Lin [8], Orchard [11]). Alternatively, interfaces are visualised with

outside projection systems that emit light on top of surfaces (Blöchl [4], Suman [14]). These

methods however are often highly complex and use expensive electronics that are purchased

as separate units. These limitations infringe development and fabrication of interactive

interface devices. Alternative processes, such as 3D printed optical displays, are in

development for simplifying and enhancing the design and fabrication of informative visual

displays. However 3D printed optic displays are often highly complex to implement with

great cost on materials, equipment, and lead time. By extending findings from previous

research in the field of interface fabrication, simple interfaces with limited active components

and low cost materials and fabrication tools can be utilised for a range of applications.

1.2 EXPLORING DESIGN SPACE The aim of this project is to design and develop an alternative process of developing

interfaces with interactive capabilities. This process will require a minimum number of

electronic components situated on a single side of a Perspex-based display. Using a single

optically clear Perspex sheet for fabrication of displays further simplifies the application

process. This enables new varieties of low cost user interfaces (UI) to be developed.

Transparent display integrated with ubiquitous computing could enable new forms of

wearable technology in future work. Eliminating the need for highly technical electronics and

greater knowledge of electrical implements interfaces could be custom fabricated for a wider

range of users. Developing simplistic processes of fabricating UIs could reduce both cost and

lead time and allow further innovation of wearable and ubiquitous technology.

With the use of laser cutting techniques interactive devices could be fabricated with greater

ease compared to other techniques such as 3D printing. Laser cutters are now more accessible

and cheaper compared to optical 3D printers and use more efficient and simplistic application

methods. Optically clear Perspex material is also much cheaper and highly durable compared

to liquid photopolymer material often used for optical 3D printing. The use of laser cut

Perspex could also reduce the number of active complements needed and decreasing manual

assembly. Three basic varieties of active components could be used to ensure simplistic

implementation. Multicolour light-emitting diodes (RGB LEDs) would provide visualisation

and enable interactivity in conjunction with other components. User interaction would be

enabled through light transmission variations within the material, recorded by a light-

dependent resistor (LDR) sensor. For simplistic computations an Arduino processing board

could be used to control any LEDs used to visualise meaningful information based on light

intensity variance. Construction using Perspex material enables low cost yet highly durability

devices to be produced. In addition, a novel process of developing interactive interfaces

enables highly customisable devices to be tailored to an individual’s needs and specifications.

Using a 2D vector based design programme, such as Illustrator, users would be able to

manually draw outlines of a desired interface. The design space would integrate 2D vector


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environments for added simplicity. This process would require minimal technical knowledge

needed compared to implementing 3D modelling for printing 3D devices.

1.3 OUTLINE OF REPORT Using laser cut Perspex material this project aims to demonstrate an enhanced process for the

design and fabrication of novel interfaces with interactive capabilities. This project aims to

present the following contributions:

1. A general approach for using laser cut Perspex prototype elements to display

information and sense user input.

2. Techniques for visualising information using laser cut optically clear material,

including use of etchings and cuts to enhance luminosity of displays.

3. Techniques for sensing user input with laser cut transparent material, a single light

source, and a sensor. This includes touch pressure input with an embedded sensor and

mechanical displacement of light wave guides.

4. Example application that demonstrates how laser cut optically clear material can be

implemented to fabricate wearable transparent interactive displays.

Firstly this report describes and evaluates current processes for rapid prototyping of

interactive interface devices and how current contributions could influence this project.

Secondly, this report explores properties of optically clear Perspex material and how these

can be exploited for visualisation and interaction. Two studies were performed to analyse

visualisation using optically clear Perspex plastic with length and angle as independent

variables. Touch studies were then performed to explore interactive capabilities using light

intensity as an input variable when pressure is applied to surface of the material. The derived

findings were then applied to prototype elements which could be integrated into active

devices that use both interaction and interface visualisation. This demonstrates a wide range

of capabilities enabled by laser cut fabrication which utilises light properties of optically clear

Perspex material. A smart watch prototype was then designed and fabricated based on

principle findings from the exploration and evaluation of pervious individual interaction and

visualisation prototype elements. The main process for designing and fabricating interface

devices with input capabilities is then described and evaluated. Finally a conclusion details a

summation of findings from the project overall, with limitations found, and future

applications of the design and development process.


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2. BACKGROUND The problem statement is to find an efficient process for fabricating novel interfaces with

interactive capabilities. It is proposed low cost rapid prototyping could be enabled by using

laser cut optically clear Perspex material and embedding active components such as a Light

Dependent Resistor (LDR) and Light-Emitting Diode (LED) for interaction and visualisation.

Discussions of relevant systems, approaches and their implications to this project are found

below.

2.1 RELATED WORK With recent development of optical quality 3D printers there is now an increase in

construction of customisable interfaces with interactive capability. This introduces great

potential for low cost and lead time device fabrication. Wills et al. [16] describe an approach

to 3D printing customizable interactive devices categorised as Printed Optics. Functioning

devices are designed within a digital 3D modelling editor and realized into a single physical

form through optical 3D printing. Active components and optical quality elements are

embedded into the device as part of the fabrication process.

The design and construction of non-flat interactive interfaces is also becoming an emerging

field of research as described by Rümelin et al. [12]. By exploring alternative display forms

which navigate away from traditional flat displays for interactive applications Brockmeyer et

al. [5] elevates the approach taken from Printed Optics to a new domain of interactive

interfaces. The system PAPILLON enables the design of curved display surfaces for

information visualisation and input capabilities through 3D modelling. The interactive device

is then fabricated through 2D optical printing as a single object. Figure 2.1 shows a toy

character with an embedded display visualising a heart shape developed through Printed

Optics (left) and another character with embedded curved display fabricated through

PAPILLON.

Figure 2.1: Device fabricated through Printed Optics [left]. Device with curved display produced through PAPILLON [right].

The current cost of fabricating such devices however is great in both material cost and

obtaining access to a 3D printer with optical printing capabilities. The majority of the devices

developed are also limited on practical use. They can be categorised predominantly as single


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value devices, as described by Mader et al. [9]. Due to multiple materials used and high

number of layers needed to produce just one device elevates lead time and cost of fabricating.

Savage et al. [13] describe a similar approach to designing and developing interactive devices

by embedding optical light tubes within interiors of 3D printed objects. Electronic sensors or

actuation components are manually embedded into the interior of 3D printed objects.

Subtractive processes are implemented through an algorithmic approach to generate space

within 3D models for insertion of active components and electronics. Through manual

insertion electronic sensors or actuation mechanisms are situated within 3D printed objects to

enable interactivity as seen in Figure 2.2.

Figure 2.2: 3D printed device fabricated through Savage’s algorithmic process of subtraction to accommodate manually embedded active components.

Baudisch et al. [2] demonstrates a tangible system, Lumino, which visualise images when

applied to diffuse illumination table surfaces, such as Microsoft Surface. Glass fiber bundle

blocks are arranged into three-dimensional (3D) structures atop an illuminated surface to

move visual focus to designated locations upon the table surface. Lumino enables custom

optimisation of a tangible visual unpowered and maintenance free system.

Takada et al. [15] presents a similar display system, Ficon, which uses properties of optical

fiber to visualise information on table-top 3D displays. Light from the bottom of a light

emitting surface is conducted up to the top of a tangible 3D display through optically clear

fiber. This allows a user to control visual displays and their position using tangible objects as

seen in Figure 2.3.

The same principle of situating a light source at the bottom of the display will be applied to

this project. However, light sources at the bottom of the device will visualise information on

the outer front face of the display. Through enhanced understanding of material properties

and limitations a fabrication process can be developed to efficiently and clearly enable

informative visualisations using laser cut optically clear material. The refinement of this

process will also ensure information could be viewed in full ambient light (sun light for

example).


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Figure 2.3: Ficon tangible 3D display devices with interactive touch capabilities through table top systems.

The fabrication processes for developing interactive interface devices discussed above are

becoming more wide spread and have great potential to change the process of how interactive

user interfaces are manufactured. However, there are limitations of using such design and

implementation processes. Optical fibres or light pipes need to be connected to a sensors of

some form to enable interactive capabilities. With the use of laser cut components there

should no direct contact between the material and sensors. Individual material components

should also be tangible and easily reconstructed for enhanced customisation without the need

to fabricate new structures. As a result lead time and cost of material consumption could be

reduced compared to 3D printing techniques.

One of the main limitations of 3D printing is that there is need for structural support when

fabricating devices with complex geometry. In some cases, device enclosures must be printed

in several parts and manually assembled to avoid structural weakness. As a solution laser

cutting could be applied to construct similar devices from robust material (Perspex sheets)

when using a 2D vector design environment. Although manual assembly would be required,

with careful design decisions the number of components needed would be reduced compared

similar 3D printed devices. Mueller et al. [10] also describe a rapid prototyping system,

LaserOrigami, that produces 3D objects significantly faster compared to traditional 3D

printing techniques using specified laser cutter settings. By stretching and folding the

material, rather than placing joints, the need for manual assembly could be eliminated.

3D printers also vary in quality of application. It is impractical to construct certain shapes

using 3D printers that are less callable of structural support. As a result it becomes unfeasible

to replication devices for open source libraries with complex geometry. Laser cutters are

higher precision manufacturing machines where quality and robustness of fabricated objects

often depends on the material used rather than the apparatus itself. The precision of laser

cutters may vary slightly, but this is often due to quality of maintenance. The LaserPro Spirit

GE, used for this project, is equipped with a sealed carbon-dioxide (CO2) laser that emits

concentrated and invisible laser radiation with a wavelength of 10.6 microns in the infrared


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spectrum. As described by Bergman and Stockman [3] the laser is the acronym for Light

Amplification by Stimulated Emission of Radiation. The CO2 laser electrically stimulates the

molecules within a carbon dioxide gas mixture. When focused through a lens, this highly-

intense, invisible beam will vaporize dense materials with high precision. Subject to speed

and intensity of the projected beam, the CO2 laser will engrave or cut through Perspex

materials of varied depths.

2.2 SUMMARY Rapidly prototyping interfaces with interactive capabilities using simplistic tools and

fabrication techniques is becoming increasingly popular. However the majority of current

contributions to this field involve complex implementation processes such as 3D modelling

and electronic assembly. The cost of material and machinery used for fabrication using

optical 3D printers for example is often high and inaccessible to general users. Lead time of

production also increases for more complex implementations. Often devices fabricated using

such approaches are defined as single-value and have little practical use. Laser cutters are

more commonly found within design spaces and require cheaper material (Perspex) which

easily accessible. Lead time is also decreased with laser cutters as often only one layer of

material is needed to produce prototypes. This makes it easier to change elements of current

devices without the need to recreate the whole device again. As a result cost of material and

lead time is reduced. Before design space for fabricate interactive interface devices using a

laser cut material can be explored there must be an understanding of material properties,

limitations, and opportunities.


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3. MATERIAL EXPLORATION In order to understand how laser cut optically clear material can be implemented to fabricate

interactive displays explorations of light properties must first be analysed. Exploring

reflection, refraction, and diffusion fundamentals aids the design and development of

prototype elements that unify to create a fully functioning interactive display. First, visual

exploration studies extend current knowledge for visualising information using laser cut

optically clear material. Secondly, interactive touch studies extend current knowledge for

sensing user input with laser cut transparent material, a single light source, and a sensor.

3.1 VISUAL EXPLORATION Two exploratory trials were conducted to uncover the effects of Frustrated Total Internal

Reflection (FTIR), as described by Han [6, 7], through laser cut clear Perspex material. The

first study investigated the affects of light transmission through a range of material lengths.

The second trial explored how angled cuts in the material affect light transmission. By

understanding how light transmission varies depending on the two independent variables

(length and angle) a model can be developed which predicts FTIR transmission through the

material.

These studies should aid designers who wish to create laser cut interactive interfaces

themselves, and also provide understanding of how sensors and switches, similar to Wills et

al. [16] Printed Optics, can be designed efficiently but using laser cut material instead.

3.1.1 DISTANCE STUDY

To extend understanding how optical light properties of clear Perspex are affected depending

on scale, a distance study was performed. How is light transmission affected with increased

distance of straight laser cut optically clear material?

Light intensity measured by a light-dependent resistor (LDR) decreases as material length

increases.

LDR readings of light transmitted through different lengths of optically clear Perspex

material are recorded. Lengths range from 10mm up to 200mm, at 10mm intervals (20

samples total). Each sample consists of a 5 second read transmitted every 10 milliseconds

from the Arduino (500 samples total). This time was chosen to analyse variation in the light

intensity over a prolonged period of time to ensure anomalies are minimised.

An Arduino UNO was connected to a NeoPixel light-emitting diode (LED) and an LDR. The

LDR was connected using a 10k resistor. All of these were mounted onto a wooden board to

secure everything in place and enable portability. A serial command was used to trigger the

experiment – input: material length (mm). The Arduino outputted a Comma Separate Values


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(CSV) data set to make it easier for R and Excel to process and output graphs. See Figure 3.1

for an image of the hardware implementation. Note how the Perspex material is held in

position using a hole in both the LED and LDR cases. This also ensures secure contact and

less escaped light between the material, LED, and LDR sensor.

Figure 3.1: The hardware used in the LDR distance experiment. Black plastic used on LDR so no light reflects.

A distance and light intensity correlation coefficient was computed to assess the relationship

between light intensity and the Perspex material length. A scatterplot summarises the results

(Figure 3.2). There was a strong negative correlation between the two variables (r = -0.96, n

= 18, p = < 0.001) that indicates light intensity decreased slightly as distance increases. This

decrease is linear which means it can be modelled easily using the data captured:

This experiment was limited to samples ranging up to 200mm; further experiments are

needed to test if the model can be used on much longer lengths of Perspex material (e.g.

1000mm). This formula can be written into an Arduino program to estimate the light intensity

drop when creating prototypes with different material lengths such as, a bracelet. The next

step in the research is to perform a similar experiment but with different angles.

LDR sensor LED light source

Clear Perspex Material

(5mm x 3mm)


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Figure 3.2: This graph shows the strong negative correlation between the means of the two variables: light intensity and material length.

3.1.2 ANGLE STUDY

To enhance the scope of fabricating interface using laser cut material, light properties of

transparent Perspex with a range of angle cuts was explored. What are the effects on light

transmission with angle of optically clear material variance?

Light intensity decreases as the angle of the material increases. Acute angles will allow more

light transmission whereas obtuse angles will transmit less light.

Record LDR readings for light transmitted through clear Perspex material, where each piece

of material has a different angle. These angles will range from 10° degrees up to 170°

degrees, at 10° degrees intervals (17 samples total). Each sample consists of the same 5

second read transmitted every 10 milliseconds from the Arduino (500 sample total). Each

material has a 3 mm inner corner radius and a length that allowed fit into the cases as

appropriate. The distance model was used to approximate the expected LDR reading for each

length of material.


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The hardware implementation was very similar to that of the distance experiment (Figure

3.3). The LED cases could be removed from the Arduino mount to accommodate the tighter

angles of material. The serial command that was used to trigger the experiment used two

input independent variables: angle of material (degrees) and material length (mm).

Figure 3.3: Arduino, LED and LRD circuit mount for angle study.

A line graph (Figure 3.4) shows both the expected LDR readings (based on material length

formula derived from the distance study) and the actual LDR readings from the angle

experiment. The difference between these lines represents the impact of the angle on the LDR

intensity. From this it can be observed that smaller angles have less impact than larger angles.

The difference is more significant for obtuse angles over 130°.

LDR sensor

LED light source


(5mm x 3mm)

at 50° angle


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Figure 3.4: This line graph shows the means of expected light intensity readings (based on the distance formula) and actual light intensity readings for every 10° variation in the material.

Two correlation coefficients were computed to assess the relationships between (a) length

and light intensity (r =-0.92, n=15, p=<0.001) and (b) the angle and light intensity (r =-0.65,

n=15, p=<0.005). From the statistics it is evident that there is stronger negative correlation in

the relationship between length and light intensity compared to that of angle and light

intensity. This means that considering length has more impact in light transmission compared

to considering angle.

From the observations taken during the experiment it was clear that more light was escaping

through the laser cut edges and corner angle of the material than the polished surface, as

shown in Figure 3.5. This is most likely due to laser induced damage where the material is

cut. These imperfections can be seen in the microscopic image in Figure 3.6.

Figure 3.5: The edges and corner of the material are illuminated brighter than the surface.

Figure 3.6: Imperfections can be seen on the laser cut edge of the material - under 30 x magnifications.


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3.2 INTERACTIVE EXPLORATION Three touch studies were conducted to evaluate interactive properties of optically clear

Perspex when light is directed throughout its core. A range of finger based input variables

were tested taking into consideration the phenomena of Frustrated Total Internal Reflection

(FTIR). Based on the findings from these touch studies a larger design space could be

explored for implementing interactive prototype elements.

3.2.1 TOUCH STUDY 1

To enable interactive capabilities of laser cut interfaces, this study demonstrates how

transparent Perspex can be used to detect touch. Can finger position on the surface of laser

cut optically clear material be detected depending on light intensity changes?

When touch on the surface of the material is closer to the LDR the variation in light intensity

is greater.

Take LDR reading of light transmission when a finger (15mm width) is applied to specific

points on the surface of the material. Material length used 130mm. Touch will be applied

every 20mm along the surface of the material. Underneath the longer horizontal piece there

will be a shorter piece of material that is 20mm in height. This shorter piece of material will

be placed 20mm away from the end of the material and will also be connected to an LDR

sensor. Using FTIR the light will travel down through the shorter piece of material when

touch is applied to the surface of the material. The first recording will be at 0mm where no

touch is applied at all to the surface of the material. Then light intensity will be recorded

when the finger is applied 20mm away from that LDR position (40mm on length of material

surface), this is repeater every 20mm until finger touch is applied at 120mm on the surface

material.

The hardware implementation was very similar to that of the distance and angle experiments.

However the LDR sensor was placed at the bottom of the smaller vertical piece of material to

take reading of light transmission (see Figure 3.7). The serial command that was used to

trigger the experiment used two input independent variables: horizontal material length (mm)

and touch distance away from the original LDR position 20mm away from the end of the

surface material.


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Figure 3.8 illustrates the average light intensity passing though the material when touch is

applied. Touch distance 0mm represents the reading when no touch is applied. Touch

distance 20mm represents when the finger is directly below the LDR sensor. This is when the

greatest light intensity change occurs as the finger is applied directly above the LDR. It peaks

dramatically compared to all of the other readings and this is due to the light rays reflecting

from the finger down towards the LDR instead of passing horizontally though material.

Figure 3.8: This line graph shows the average light intensity from the bottom of the material when touch is applied. Touch distance 0mm represents that no touch is applied and touch distance 20mm represents when

touch is applied directly above the LDR sensor.

Figure 3.7: Arduino, LED and LRD circuit mount for touch study. Finger is applied at 20mm where the LDR is positioned. Then touch is applied every 20mm along

the surface until 120mm distance is reached. No touch is applied at 0mm distance.

LED

light source

LDR

sensor


(5x3x130mm)

Material

length 20mm


Page 21 of 68

Considering that 0mm touch distance represents no touch applied it is evident that there is a

slight decrease in light intensity when the finger is applied further along the surface of the

material, after the initial 20mm mark. This means that some of the light reflecting downwards

into the LDR is lost/absorbed when single finger touch occurs away from the LDR.

From these results two observations can be made:

1. When finger touch is applied directly above the LDR sensor more light rays travel

down through the shorter vertical Perspex material that is connected to the LDR

sensor, this FTIR phenomenon increase the light intensity LDR reading.

2. When comparing no touch with touch further away from the LDR there is a slight

decrease in light intensity. This could be due to the light rays being disturbed earlier

when reflecting through the material and thus more rays escape before reaching the

LDR.

From the results found during the touch study it was found that interactivity can be achieved

using light intensity as a variable input. A simplistic button action can be developed where

the user could activate a command by applying pressure touch to a particular part of the

material surface where the LDR is located. This interactivity is achieved though FTIR

variations. Light transmission changes can also occur when touch is applied at further

distances away from the LDR a simple two state variable interactive interface can be

developed. A simple control system (see Figure 3.9) could be created, where light

transmission increase is detected using the LDR and the volume of speakers can also

increase. When relatively low light intensity decrease is recorded then the volume is turned

down.

Figure 3.9: Volume control device concept using a strip of clear material, an LED light source, and an LDR sensor.

Human finger

Clear material

LED light source

LDR underneath

clear material

Speaker volume increases

when LDR reading is high and

decreases when LDR

reading is low


Page 22 of 68

3.2.2 TOUCH STUDY 2

To enhance the range of user input capabilities, a study explores possible correlation between

position of a finger and the resulting light intensity. Can finger touch position be detected

depending on light intensity changes when an LDR is placed directly opposite an LED?

When touch is applied on the surface of the material close to the LDR the variation in light

intensity is greater.

The LDR reading of light transmission will be taken when a finger (15mm width) is applied

to specific points on the surface of the material. Material length used 130mm. Touch will be

applied every 10mm along the surface of the material. The LDR sensor will be located

directly opposite the LED light source and connected to the material (5 x 3 x 130mm in

dimensions). Using FTIR the light will travel through the material and when touch is applied

to the surface light rays reflecting within the material will be disrupted and more light should

escape through the material before reaching the LDR sensor. The first recording where touch

is applied will be at 10mm away from the LDR. This is repeated at intervals of 10mm until

the touch applied is 120mm away from the LDR (12 samples total).

The hardware implementation was very similar to that of the distance and angle experiments

where the LDR sensor was placed directly opposite the LED on the other end of the material

as seen in Figure 3.10. The serial command that was used to trigger the experiment used two

input independent variables: horizontal material length (mm) and touch distance away from

the LDR starting at 10mm on the material surface.

Figure 3.10: Arduino, LED and LRD circuit mount for touch study 2.

LED

light source

LDR

sensor Clear Perspex Material

(5x3x130mm)


Page 23 of 68

Figure 3.11 shows a decrease in light intensity up until touch is applied 50mm away from the

LDR on the surface of the material. Then there is a high increase in light transmission in

when touch is applied between 60mm and 70mm, followed by another decrease at 80mm

distance. This result was unexpected and another sample of data was collected when

repeating the experiment to ensure these results were valid.

Figure 3.11: Average light intensity from the first data sample collected.

This shows an irregular pattern that was not expected.

Figure 3.12 shows the second data sample has even greater disparity. Overall the data has

high variance between samples and there is no consistent relationship found between the

touching distance ad light intensity when one finger is applied on a particular point on the

surface of the material when the LDR is positioned directly opposite the LED light source.

Figure 3.12: Line graph visualising the average light intensity from the second data sample collected.

This shows even more irregularity that was not expected.


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3.2.3 TOUCH STUDY 3

This study explores if laser cut material could enable multi-touch interaction based on light

intensity changes corresponding to number of fingers applied to the surface. Does applying

pressure with multiple fingers effect light intensity when the LDR is placed directly opposite

the LED?

When touch is applied with more than one finger on the surface of the material light intensity

decreases.

Take LDR reading of light transmission when a finger (15mm width) is applied on the

surface of the material. Material length used 130mm. Record light intensity when additional

fingers are touching the surface one at a time until 10 samples are collected.

The hardware implementation was very similar to that of “touch study 2” experiment where

the LDR sensor was placed directly opposite the LED on the other end of the material as seen

in Figure 3.10. Multiple fingers were applied to the surface of the material and light intensity

was recorded for sets of fingers in close proximity. Starting from 1 finger and incrementing

until 10 fingers were applied to the surface of the material. The serial command that was used

to trigger the experiment used two input independent variables: horizontal material length

(mm) and number of fingers applied on the material surface.

As the number of fingers on the surface of material increase, light intensity within the

material decreases (see Figure 3.13). The application of a large number of fingers on the

surface of the material can be used as a form of user input.

Figure 3.13: Light intensity decreases as the number of fingers on the surface of the material increases.


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3.3 DISCUSSION AND SUMMARY This chapter considers visual and interactive explorations of optically clear material to enable

efficient fabrication techniques for prototyping interactive interfaces. In terms of visual

capabilities, a linear model of light transmission was derived through various lengths of

material. This showed that light intensity through the material was constant, even with

ambient light present, yet varied with material length. In terms of interactivity, touch could be

detected using an LDR to read any changes of light intensity exploiting FTIR variance. To

apply scope to the explorations some parameters were not explored such as width of material

impact on light intensity. Those selected for exploration had greater impact on devices

fabricated for this project.

To increase validation of studies performed large sample sizes (n=500) were used to

minimise anomalies. Independent variables were sampled in fixed steps such as length

(between 10mm to 200mm, every 10mm) and angle (between 10° to 170°, every 10°) as it

would be impractical to laser cut every possible angle. Although observations have not been

obtained beyond these ranges, additional findings are expected to follow the same model. In

terms of interaction, only finger based interaction was explored. This limits the exploration of

alternative input possibilities such as use of stylus pens. However given prevalence of touch

based interaction this method is justified.

In future studies an extended range of material lengths and widths should be tested to gain

enhanced understanding of impact on larger scale implementations. In addition, alternative

methods of input interaction should also be explored to further explore possibilities of

expanding the design space for prototyping interactive displays.

In conclusion the work in this chapter enables the design and fabrication of interface

prototypes such as switches, sliders, and touch detection. These can be a range of sizes and

shapes as explored through the studies. In the next chapter this is built on by creating

fundamental prototype elements such as switches and displays. This enables the construction

of a prototype that combines all of these elements.


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4. PROTOTYPE ELEMENTS This chapter details meaningful uses of properties found from the previous light explorations.

Single systems for interaction and information visualisation are implemented for a range of

applications. These single systems can later be combined to produce a fully functioning

interfaces prototype with interactive capabilities.

4.1 INTERACTIVE APPLICATION ELEMENTS Developing simple user input prototype elements demonstrates principles found in the

exploratory interactive studies. Simple interactive prototype mechanisms can later be

implemented in a variety of scenarios. The first sub-section of the chapter focuses on

application examples demonstrating how laser cut device components could enable user

interaction through displacement of light. The second sub section expands on how laser cut

devices could be used to display meaningful information without the need of electronics

situated behind the interface or even projected atop the surface.

Prototype elements produced for this chapter:

Button light switch

Accelerometer

Seven-Segment Display

o Light sources situated around four sides of display.

o Light sources only situated on one side of display.

4.1.1 BUTTON

The button element (light switch) was based on interactivity principles discovered from three

touch studies performed. It was found that optical sensing could be achieved through push

and pressure application to the surface of the material. By embedding optically clear material

into an enclosure fitted with a separate light source, a light switch mechanises was produced.

The principle input variable for this device was based on light transmission displacement

recorded by a standard light-dependent resistor (LDR). The light switch device would be

separated into two elements. First, clear Perspex material with light transmitted through it

(LED 1) would be used as an actuator that senses user input when pressure is applied to the

surface. This would be achieved through Frustrated Total Internal Reflection (FTIR)

phenomena and recorded using an LDR sensor positioned below the material. Secondly, a

light source (LED 2) would be activated when light intensity readings (LDR with a 10k

resistor) reach a specified threshold. This threshold is calculated by sampling light intensity

behaviour when pressure is present on the surface of the material. The colour of LED 2

would change depending on the amount of level of pressure applied to the surface.


Page 27 of 68

Apparatus used:

1. 2x LEDs - first for clear material and second as output to visualise interactivity.

2. 1x LDR - sensing light intensity through material.

3. 1x Arduino Uno - computing interactivity variable.

An enclosure was first fabricated by laser cutting three pieces of black material (dimensions:

180x25x3mm). Each of the three layers had specific cavities cut to accommodate three

electronic apparatus need for the device. The bottom layer had three cavities to house both

LEDs and LDR that would be situated in the two layers above. The middle layer also had

three similar cavities. The main cavity of the middle layer (dimensions: 3x5x3mm) was for

the LDR sensor. It ensured the LDR would be situated directly below the clear material that

would be placed within a frame above. Finally, the top layer consisted of a cavity frame to fit

a piece of optically clear Perspex (dimensions: 110x5x3mm) with a slot to fit LED 1 on one

side, 50mm away from the LDR cavity. The other slot is cut into the top layer 35mm away

from the interactive elements of the device (dimensions: 5x5x3mm) where LED 2 is situated

without impacting the light intensity reading from the LDR. The use of LED 2 is

predominantly to visually demonstrate user input capabilities. The enclosure was assembled

using four nuts and bolts, one situated at each corner of the rectangular enclosure.

Once all three electronic components were soldered and placed within the enclosure into their

designated cavities an optically clear piece of material was cut and placed within the frame of

the top layer, with corresponding dimensions to the frame (110x5x3mm). This material piece

could be taken out of the enclosure with ease in order to deactivate the device. Figure 4.1

shows the fabricated button light switch.

Figure 4.1: Button light switch when no interaction occurs.

Based on the findings from the previous touch studies, light intensity through the material

should increase when enough pressure is applied to the surface at a specific point when

ambient light is present. The LDR sensor situated directly below the point of contact records

light intensity changes when pressure is applied. When pressure was applied directly above

the LDR, a 5 second read transmitted every 10 milliseconds (500 sample total) was averaged

and used as a threshold for activating LED 2. Subsequently, the same process was applied

LED 1 light source

LDR sensor under transparent

material


(110x5x3mm)

LED 2 visualising interactivity


Page 28 of 68

when finger pressure on the surface of the material was relatively light or when the finger

was hovering over the surface. The average reading from this second sample was used as the

second threshold for activating a different colour light from LED 2 when light intensity

decreased.

A basic light switch device was designed and fabricated based upon interactive principle

discovered during the exploratory touch studies. A simplistic enclosure was designed where

clear Perspex material could be placed into a fitted frame. Finger pressure of the user was

treated as an independent variable. Light intensity transmission was therefore treated as a

dependant variable and used as an input measurement for light switch actuation. User input

was achieved by sensing light intensity change caused by FTIR. Using a low-cost LDR

discretely situated within the enclosure three threshold sates were used as input variables to

activate a light source (LED 2). Hard finger pressure applied to the surface defines high state

and LED 2 emits pink light. When light finger pressure is applied low state (decrease in light

intensity) is achieved and LED emits yellow light (Figure 4.2). When no finger is present, the

device is set to no state and LED 2 is deactivated.

Figure 4.2: As pressure on the surface of the material increase LED 2 changes colour from yellow to pink.

It was found that these three states could only be achieved when enough ambient light is

present in the test environment. When no ambient light is present only two states could be

achieved. When any form of pressure is applied to material surface at a point directly above

the LDR, light rays are directed towards the receiver hence only allowing for light intensity

increase.

4.1.2 ACCELEROMETER

A simplistic accelerometer was developed which was actuated through displacement of light

guides present within a thin strip of material that was situated in a small black enclosure to

avoid ambient light affecting any readings. This device monitors movement displacement

from the outside environment. Further displacement is also caused by effects of gravity due

to the strip drooping slightly downwards.

Low State Light Intensity

Decrease

High State Light Intensity

Increase


Page 29 of 68

A case enclosure would house a small strip of optically clear material with a wider, heavier

section cut on the end in order to enhance the effects of outside motion. A light source would

be positioned at one end of the enclosure in a cavity to illuminate the clear strip of material

within. A light-dependent resistor (LDR) should be positioned at the other end of the case. As

the light-emitting diode (LED) rays travel through the thin material any outside displacement

should affect the thin, clear strip. As a result it should move away from the LDR, hence

causing a change in light intensity reading.

Apparatus:

1. 1x LED

2. 1x LDR

3. 1x Arduino Uno

The fabrication of the accelerometer is separated into two sections. First, a small rectangular

enclosure was cut from 3mm black Perspex material (dimensions inside: 93x19x19mm). Two

openings were cut at each end of the enclosure. The first opening (dimensions: 5x5mm) for

situating an LED. The second opening at the other end of the enclosure (dimensions:

5x3.5mm) was cut to accommodate a standard LDR. This rectangular box enclosure was

assembled in place with acrylic adhesive. The top section was detachable to enable the

placement of the clear material strip. Six vertical sections were etched parallel to each other

along the inside walls of the case (dimensions: 4x19x0.5mm). These were used as

placeholders for a smaller piece of material that will hold the optically clear strip of Perspex.

The small piece of black material was cut separately (dimensions: 20x19x3mm) with an

incision measuring 4mm in width and 1mm in height, directly at the centre. This “strip holder

piece” was placed securely inside of the enclosure by sliding it into one of the etched sections

located within the case. Sensitivity of the accelerometer could be changed by positioning the

“place holder” piece closure to the LDR.

Secondly, an optically clear strip was cut from 3mm material. The optimal width of cut to

ensure flexibility yet durability for the strip was 0.72mm with the length of 94mm. A larger

section was cut on the strip, 9.9mm away from the end (dimensions: 5x3mm) in order to

enhance the effect of displacement outside. Figure 4.3 shows the accelerometer produced

from laser cut material and two active components.


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Figure 4.3: Accelerometer prototype (top not present) with LED and LDR situated

opposite sides of rectangular enclosure.

In order to identify any displacement characterisation the independent variable for this study

was based on velocity. Firstly the independent variable incorporated vertical velocity by

repeatedly shaking the device up and down. Light intensity was considered as the dependant

variable and readings were recoded using an LDR for a period of 1.7 seconds. The

independent variable changed to incorporate horizontal movement and the device was shaken

from left to right on the horizontal axis. Light intensity readings were recorded for 1.7

seconds. Figure 4.4 illustrates the comparison between horizontal and vertical displacement.

Figure 4.4: Comparison of vertical and horizontal displacement based on light intensity.

The local maxima of light intensity for vertical movement is much higher (200±10 LDR

reading) compared to that of movement performed on the horizontal axis (170±10 LDR

reading). The device worked relatively well when constant displacement on a specific axis

occurred. However, it is difficult to observe the exact behaviour of the material strip as the

active components are enclosed within the case. Performance can enhanced if material length

was shorter as more light would reach the LDR. Due to high variance in readings throughout

prolonged periods of time and lack of touch based interactivity the accelerometer would not

be featured in the final application.

LED light source

LDR sensor


(94x3x0.72mm)

Material Strip Holder with incision

(20x19x3mm) Cushion


Page 31 of 68

4.2 INTERFACE APPLICATION ELEMENTS Seven-Segment Displays (SSD) visualise meaningful information through individual state

transformations of single characters or numerals. Two SSDs were designed and fabricated

using laser cut Perspex material. The initial SSD, with seven LEDs around all four sides, was

produced to explore light guide manipulation. The initial display illuminated isolated

segments in a specified order that mimicked state changes of a conventional SSD. After an

efficient design approach was established, a second SSD was implemented where light

sources were situated only at the bottom of the display. This chapter details the process of

design and fabrication for both displays, including discussion of design decisions made to

develop an efficient approach to illuminating various states of an SSD.

4.2.1 INITIAL SEVEN-SEGMENT DISPLAY (LEDS AROUND 4 SIDES)

The initial SSD was developed in two stages. First, a 2D vector outline of an enclosure was

designed in Illustrator to specific measurements of 85x120x9mm (see Appendix Figure 3).

Three layers of laser cut black Perspex plastic (3mm depth) were combined and assembled

using 3mm nuts and bolts. The top layer of material was a frame where the clear Perspex

display could be placed. Seven LEDs were chained together and interlinked within seven

slots of the enclosure. Each LED was specifically positioned within the frame to illuminate

only one designated segment (see Figure 4.5). The frame was designed to hold material

within the measurements of 65x100mm. Secondly, a number of displays were designed and

laser cut out of clear material with depth range from 3mm to 5mm. The observations from the

range of laser cut and etched displays can be found below.

Figure 4.5: SSD enclosure (85x120mm) consisting of three layers with LEDs positioned on all four sides.

Each LED light source

with a number allocated to it

Transparent display should be

situated within the frame

(65x100mm)


Page 32 of 68

4.2.2 INITIAL LIGHTING OBSERVATIONS

A range of SSD designs was explored and eight test cases were implemented in order to

determine a proficient solution to illuminating isolated segments of an SSD (for full recorded

observations see Appendix Table 1). A range of etching styles and depths was also explored

to find an efficient approach for enhanced illumination. In an attempt to manipulate light

guides a range of cuts with varied widths and positions were also tested. Each segment was

uniform in shape (elongated hexagons) and relative to each other in size. In order to observe

light distribution effects an individual etches, each segment was scaled to maximum size of

12x37mm in the first four tests. All segments of the display were illuminated even when

black tape was applied to the top of active LEDs in an attempt to eliminate any ambient light

emitted. Full matt etch are coarse and do not distribute light rays evenly throughout a whole

segment. Matt etches reveal the direct path of light from a light source as seen in Figure 4.6.

Figure 4.6: Test 1 with five active LEDs illuminates all of the seven segments and visualises light path from LED sources proficiently on matt etches.

For light rays to be distributed more consistently throughout each segment a crisscross

pattern was designed to defuse refraction. Figure 4.7 shows the initial 2D vector design of the

pattern and result.

Direct light path from LED light source is clearly visible

on matt etches


Page 33 of 68

Figure 4.7: Criss cross pattern etches distribute light rays more consistently compared to flat matt etches.

To enhance luminosity of each active segment a range of cuts were made on the surface of

the display and impact of illumination for each segment was observed. Diagonal cuts (0.1mm

width) correlating to each segment efficiently brightened etched areas closest to the cut as

seen in Figure 4.8. This was due to light refracting within air gaps and this intensified the

effect of emitted light rays. Real life observations show the right segments illuminated

brighter compared to the middle section.

Figure 4.8: Cuts from test 9 enhances illumination of five segments.

In order to isolate light emitted from an LED to a single designated segment, black insertions

were designed and placed into the display. The width of cuts was increased to 1mm width

and black material (3mm depth) was cut corresponding to cavities in the transparent display.

The black material inserts (1mm width) isolated each of the seven sections of the SSD and

occluded light rays reaching inactive segments. Several refinements were made to the

position and design of the black inserts until a proficient implementation was found. As seen

in Figure 4.9 black inserts enable each segment to be illuminated individually without light

effective adjacent segments.

2D vector design

LED light rays evenly distributed within a segment

Cuts made in close

proximity to segments

enhance their brightness


Page 34 of 68

Figure 4.9: Design and applied SSD with black material insert that isolates each segment of the display.

Black inserts occlude light rays from reaching inactive segments. Further refinements to the

design of cuts enabled clear interchangeable states of numerals to be displayed in various

colours when ambient light is present as seen in Figure 4.10.

Figure 4.10: SSD displaying digits from 0 to 9 in a range of colours in full ambient light.

The display is able to visualise each of the 128 states of an SSD with LEDs situated around

all four sides of the enclosure. To refine the design further LEDs where positioned only at the

bottom of the display. A second SSD prototype was fabricated, using the same design

approach, where seven LEDs were situated only on the bottom of the frame.

2D vector design Display produced

A singular black insert

isolates each segment to

reduce number of

components needed for

assembly


Page 35 of 68

4.2.3 REFINED SEVEN-SEGMENT DISPLAY (LEDS ON BOTTOM)

Much like the initial SSD, the second display consisted of an enclosure made from three

layers of black Perspex material (depth 3mm) with the top layer acting as a frame for a clear

display. The prototype was scaled up to a larger size (120x140x9mm) for the enclosure, with

frame area 100x120x3mm. Seven LEDs (9mm width each) were soldered to create a

sequential chain (length 80mm). Once the LEDs where set up within the enclosure, the design

of the initial SSD layout was readjusted to accommodate the new LED alignment.

The first redesign of the SSD reflected upon Wills et al. [16] implementation of digital

signage, where ten layers are used for visualising individual numeric figures. For the refined

SSD two layers of material created an interface that visualised single figures with light

sources directly underneath the display. The bottom layer consisted of clear material (5mm

depth) divided into seven individual light tubes, one for each segment. Each light tube was

situated directly above a designated LED that emitted light rays to a corresponding segment.

The light tubes were extended below a selected etched segment. Large cuts were made

directly below the etched pattern to intensify luminosity of etched segment above. The top

layer was implemented by applying a similar design as the initial SSD. Figure 4.11 shows the

two layers SSD with light sources below the enclosure. This implementation provided low

luminosity and could be refined further by reducing the number of layers.

Figure 4.11: Two layer SSD with LEDs only at the bottom of the enclosure.

Top layer etched segment

illuminated from light tube

situated underneath

Chain of seven LEDs

Bottom layer light tube

emitting light to top segment


Page 36 of 68

A refined version of the initial SSD display was implemented with a single layer of material

(5mm depth) and corresponding black inserts (5mm depth). Elongation of black inserts

ensured light emitted from adjacent LEDs did not affect inactive segments (see Figure4.12).

In order to fully partition each segment and ensure no light escaped to inactive segments, the

display was divided into separate five sections. As this prototype used a frame based

enclosure the prototype could stand vertically without any need for adhesive.

Figure 4.12: Single layer SSD design with black inserts and final implementation of

an SSD displaying the figure “4”.

4.3 DISCUSSION AND SUMMARY This section of the report evaluates all prototype elements produced and their purpose for the

next stage of application. A breakdown of the design and fabrication process for developing

successful SSD displays with light sources situated only on one side can also be found below.

Breakdown of design and fabrication process for developing an efficient SSD display:

1. Design simple enclosure in proportion to length of LED strip.

2. Laser cut black Perspex material to corresponding design.

3. Assemble and insert LED strip.

4. Design seven-segment display with enough space between each segment to insert

1mm width black material.

o Add lines (1mm width) to partition each segment of the display.

5. Laser cut setting for most effective result for etches and cuts varies depending on

material depth please see Appendix Table 1 for details for 5mm depth material.

6. Once the display is cut and etched corresponding cuts must be made to black material

of the same depth and inserted into the display where appropriate.

Two black inserts partition the display into five sections


Page 37 of 68

With influence from the initial SSD design, black inserts are redesigned to accommodate

light sources that are situated underneath the display. These interfaces are highly robust and

could be submerged in water. Using only one layer of material eliminates the need for

electronics to be present in the actual interface.

Wills et al. [16] implemented a similar display system using 3D printed rectangular blocks

with air pockets. Wills et al. [16] developed a nixie tube style numeric display consisting of

numeric figures embedded into ten 3D printed sheets. The SSD interface developed for this

project uses one layer of material produce the same outcome with a light source enabling

illumination of numeric digits. Figure 4.13 shows a comparison between both displays

Figure 4.13: Printed Optics numeric display (a) consisting of embedded air pockets that reflect light when illuminated (b). The numeric display fabricated through laser cutting (c) in contrast only uses one layer of

material to visualise figures 0-9.

Fabricating interfaces from a single material enables new kinds of cheaper wearable

technology to be utilised. The next stage is to apply this design and fabrication process on a

smaller scale in order to prove it can be implemented as a transformative process. Using the

example of a smart watch ensures the SSD design could be used effectively to display

meaningful information on a transparent interface on a smaller scale in a novel manner.

In term of interaction, light intensity readings were affected by presence of ambient light

within the test environment. If ambient light from the environment was to constantly change

the configuration of the device must be monitored and reset to accommodate the ambient

light changes. This may decrease accuracy of the device. Nevertheless an algorithm could be

computed that eliminates any form of ambient light. Alternatively, an algorithm could

monitor changes in the environment (using a separate LDR) and notify a user when ambient

light displacement occurs and recalculate threshold levels when pressure is applied and not

applied to material surface. This could be done also by adding a compositor to the LDR

circuit.

In conclusion, the work in this chapter demonstrates prototype elements that can be fabricated

as single systems. In order to create a fully functioning prototype both interactive and visual

elements must be integrated. In the next chapter this is built on by creating unified prototype

interactive watch that is activated through user input to visualise current time.


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5. APPLICATION - WATCH PROTOTYPE This chapter details the design and production of a watch device as a final proof of concept

based on the alternative fabrication process developed from preceding chapters. The final

prototype integrates application elements from previous studies and applies it in a ubiquitous

context to develop a wearable device. This final prototype incorporates the interactive

properties of clear Perspex material discovered from the touch studies and button light

switch. An interface was conceptualised and developed based on the design and fabrication

process used to create an SSD interface.

The proposed smart watch should be small in scale and display current time using individual

numeric figures sequentially on a single later of optically clear material. An interactive button

would be used to activate the display. When a user applies sufficient level of pressure to the

surface of the material a change in light intensity, measured by a light-dependent resistor

(LDR), will occur. This will be used as an actuation command to display current time on the

interface.

5.1 LED ENCLOSURE First, a chain of seven RGB Light-emitting diodes (LEDs) was soldered together. Each LED

(dimensions: 5x5mm) was designated to illuminating one segment of the SSD. The total

length of the LED chain was 70mm. In future work much smaller surface mount RGB LEDs

(dimensions: 3x3mm) could be used to bypass the current limitation of scale. Each LED was

5mm in diameter with a 5mm space between each to limit light dispersion from adjacent

LEDs. A rectangular enclosure, consisting of six sides with finger edge joints was designed

(see Appendix Figure 6) with seven cavities (spaced 5mm apart) to house each of the LEDs.

Black material (3mm depth) was cut into six sides corresponding to the 2D design from

Illustrator. Acrylic adhesive was applied to finger edge joints to secure the rectangular

enclosure leaving the top side open (dimensions: 90x15x15mm). The LED chain was

manually inserted into the enclosure. Figure 5.1 shows the constructed LED enclosure.

Figure 5.1: LED enclosure for watch prototype with chain of seven LEDs situated inside.

LED light source

Black Perspex Material Enclosure

(90x15x15mm)


Page 39 of 68

5.2 INTERFACE The second stage of development involved adapting the previous SSD interface design

(dimensions: 100x120x5mm) to a smaller scale for a watch display. Although the enclosure

for the LED chain is 90mm in length the interface is much smaller to ensure discreteness as a

ubiquitous device. The display integrates a generic SSD interface (dimensions: 40x40mm)

with a rectangular extension that increases the length of the entire display by 10mm (see

Appendix Figure 7 for design outline). By extending the width to 80mm the display can

accommodate the larger enclosure situating the chain of seven LEDs. The whole interface

was 5mm in depth and included seven 3mm extensions at the bottom (see Figure 5.2). This

enabled the interface to be inserted firmly into the LED enclosure without need for adhesive.

Figure 5.2: Refined display for interactive watch prototype. Consisting of optically clear Perspex (depth 5mm) and corresponding black material partitions (width: 0.72mm).

The previous SSD design with black inserts was scaled down to accommodate the main

40x40mm interface with an elongated extension. Initially black cuts were simply extended to

the bottom of the display to isolate each of the individual LEDs. The width of cut was also

decreased to 0.5mm in order to reduce the presence of black material in the interface. The

initial display was cut from 5mm clear material with corresponding black material inserts.

The whole interface consisted of five separate segments and two black inserts. Acrylic

adhesive was used to secure the structure and ensure robustness and stability as a watch. It

was discovered that the use of acrylic adhesive disrupted the reflective properties of the clear

material when contact was made with the black inserts. This eliminated the reflective edges

of the cuts as seen in Figure 5.3. The reflective properties of the display were reduced if too

much adhesive was used.

Black material

inserts

Material

extension to

accommodate

chain of LEDs

Extension for

enclosure insertion


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Figure 5.3: Initial watch interface (secured with adhesive to ensure robustness) inserted into LED enclosure.

The initial interface design (see Figure 5.4) visualised each of the ten states needed to tell the

time using digits 0-9. However the top right segments did not illuminate well compared to the

other five segments. This was due to the limiting angle at which the etched segments were

located, i.e. 20mm away from their designated light sources. As a result the first display did

visualise figures proficiently in ambient light. Even when a darker background was used the

luminance of visualisation was not proficient. A fascia was used in an attempt to enhance the

visualisation of each etched section. However, the addition of a fascia did not enhance the

display as predicted.

Comparison of colour and etch observations highlighted current visualisation issues with the

initial design. The figures “6” and “9” were illuminated in order to inspect the majority of

segments. The refinement of the second interface (see Figure 5.5) was based on visual

inspection of angles and position of black inserts and etched sections with correspondence to

designated light sources.

Area where

adhesive makes

contact with

the clear black

material

Area where no

adhesive

contact is made

with the clear

black material


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Figure 5.4: Due to angle restrictions the initial design of the display did not allow light to be transmitted efficiently to the top sections as shown by numerals 6 and 9.

Certain colours enhanced the visualisation of etched section with more clarity as seen in

Figure 5.4. The colour green for figure “6” is much more prominent compared to figure “9”

illuminated in yellow.


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A second design was implemented with minor adjustments to angles of cuts and low edge

corners to ensure each segment is illuminated proficiently in full ambient light. Figure 5.5

compares prominence of illumination applied using the same figures for consistency.

Figure 5.5: Refined design of the display enhanced illumination of both figures regardless of light or dark background and the addition of fascia.

The refined design considered angles of each black cut and expands areas of clear material

for each sections of the display where light rays struggled to have reached previously. The

initial design the colour yellow did not illuminate etched sections proficiently. The refined

design enhances the visualisation of each segment even when a yellow light source is used.


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5.3 INTERACTIVE BUTTON A separate enclosure was designed for the interactive button element (dimensions:

90x15x9mm). This was a scaled down version of the original design based on the initial

button light switch. The button element could be scaled down even further for future work,

however in order to keep aesthetic consistency it was designed to be the same diameter as the

LED enclosure (see Appendix Figure 8 for laser cut outline).

The button enclosure consists of three layers of black material (3mm depth) with cavities for

an LDR to be situated in the middle layer and another cavity for an LED in the top layer. The

top layer acts as frame where clear optical material is inserted and is considered an actuator

for interactive capabilities. A standard sized LDR was used (dimensions: 5x4x2mm) as

smaller LDRs were too sensitive and picked up the frame rate of the LED. A capacitor could

also be added in future work to defuse frequency displacement. As the standard LDR did not

impact scale is was implanted instead. By excluding the need for a capacitor less electronic

components are required.

Three layers of laser cut black material are assembled together with active components

situated within designated cavities. A piece of clear optical material is cut corresponding to

size of the top layer frame (dimensions: 71x5x3mm) and is considered as the actuation

component for the interactive button. Figure 5.6 shows the final watch interactive button.

Figure 5.6: Button actuation device consisting of one LED, one LDR, and a strip of optically clear material.

User input must be configured, with consideration of ambient light, on the surface of the

material. First, light intensity average is calculated when no pressure is applied to the surface,

this is used as an actuation threshold for the watch. Secondly, light intensity average is

calculated when no pressure applied to the surface. This is used as a threshold to deactivate

visualisation if undeliberate interaction occurs. Ambient light in the environment must also

be taken into consideration as this disrupts readings from an LDR which is very sensitive.

Implementing a compositor in further work could eliminate ambient light noise from LDR

reading.

LED light source

LDR sensor

Transparent material (71x5x3mm)

Button element enclosure (90x15x9mm)


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5.4 FINAL INTEGRATION Once the final interface was assembled a watch strap was designed to hold the watch on a

human wrist. The strap design was separated into two sections, one of each side of the

display. Hinges secured with adhesive enabled the user to adjust the tightness of the strap.

The combined light enclosure, interface, and interactive button produced a wearable watch

with interactive capabilities. The interface visualises each digit of current time in sequential

order once finger pressure is applied to the button. Performance was tested in ambient light

for quality in visualisation and interaction. Interactivity of the button was efficient when used

in an environment where ambient light levels did not change. Interactivity of the button did

not change when no ambient light was present. Figure 5.7 shows numerical digits visualised

on the interface. Each number can be distinctly identified and shown in a range of colours.

Due to the incoherent white balance of the camera used (IPad 4 camera) luminance of the

display is not as prominent in photographs. Nevertheless visualisation is enhanced when no

ambient light is present. A comparison of the display with no ambient light can be seen in

Figure 5.8.

Figure 5.7: Figures 0 to 9 displayed on final watch prototype in full ambient light. The middle section is no as

well illuminated compared the surrounding sections.

A range of colours was used to visualise individual digits to examine if certain colours enable

figures to be distinguish further. When ambient light is present red, green, and blue colours

were more distinguishable as seen in Figure 5.7. However, colour changes had little effect in

the visibility of figures when no ambient light was present.

Figure 5.8: Figures 0 to 9 displayed with no ambient light present. Each figure is visualised with greater clarity

though the middle segment is still less obvious.


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5.5 DISCUSSION AND SUMMARY This chapter demonstrates the integration of singular active prototype elements into a unified

watch device with interactive capabilities. The example application proves how laser cut

optically clear material can be implemented to fabricate a wearable interactive display.

The combination of the LED enclosure, interface and interactive button enabled fabrication

of a purposeful interactive device that can be used in both darkness and daylight as seen in

Figure 5.9. By applying the design and fabrication process in context of wearable technology

it was demonstrated that interface scale should not be an issue in the design space. The main

limitation for this application was the large size of LEDs used. This means that the light

enclosure could not be discrete. In terms of visualisation, the luminosity of figures could be

enhanced further by limiting the space between the LEDs. With further refinements to the

discreteness of active components, by using smaller LEDs for example, devices could be

scaled down much more. Visualisation of meaningful information on transparent surfaces

enables further exploration of design space for new forms of interfaces.

Figure 5.9: Watch used when no ambient light is present compared to when ambient light is present.

In terms of interactivity, the button element was able to activate the display when ambient

light levels within the test environment stayed constant. If levels of ambient light increased a

new threshold levels must be set higher than previously to accommodate the change.

Otherwise the button would be activated with the present of ambient light. By adding a

capacitor to the LDR circuit ambient light is eliminated from the LDR readings.

WATCH USED WHEN NO AMBIENT LIGHT IS PRESENT

WATCH USED WHEN AMBIENT LIGHT IS PRESENT


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This would mean the addition of an extra electronic component to the fabrication process. An

alternative algorithm approach could also be implemented to eliminate effects of ambient

light affecting the light sensor.

The watch device could easily be customised by simply replacing detachable sections with

alternative objects. The transparent display is detachable from the main enclosure. This

allows users create new interfaces and replace them easily without the need to fabricate a

whole new device. Cost of material and lead time as a result is greatly reduced compared to

3D printing. The design decisions utilised in this report enabled the laser cut devices to have

detachable parts. This presents a rapid prototyping process of exploring design decisions

without the need to wait for creating a whole new object is enabled as components can easily

be replace from an existing object.

In conclusion the work in this chapter enables the design and fabrication of a fully interactive

watch prototype. The next chapter describes the fundamental process and approach to

fabricating interactive display prototypes.


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6. DESIGN CONSIDERATIONS AND DISCUSSION The process of developing interfaces with interactive capabilities described in this chapter

consisted of three phases. First, optically clear material light properties were explored for

enabling visualisation and interactivity. Secondly, findings and observation were applied to

physical examples of single systems. Thirdly, a group of single systems were integrated to

produce a functioning interface device with interactive capabilities as a validation of the

process described in this chapter. Below the design considerations are presented to design and

fabricate interactive interfaces from laser cut Perspex.

6.1 APPARATUS The apparatus consists of a hardware processing board, RGB NeoPixel Mini PCB LEDs

(datasheet details can be found below here1), and a standard sized light-dependent resistor

(LDR). Use simple transmitter and receiver components.

1. Computer aided design (CAD) software

a. 2D vector graphic tool - such as Illustrator.

2. Hardware

a. Arduino processing board (such as Uno, Mega, mini, or Nano).

3. For interactive element

a. 1x LED for emitting light rays.

b. 1x LDR for receiving emitted light rays.

4. For display

a. X number of LEDs corresponding to the number of sections required for the

display - E.g. seven-segment display use seven LEDs in a chain (one to

control illuminate each section individually).

6.2 DESIGN AND FABRICATION OF ENCLOSURE Design an enclosure to house active components in a 2D vector based design space,

Illustrator CC used for this project. An enclosure is needed for situating electronic elements.

1. Draw outline of desired enclosure with cavities to expose LEDs and LDR to

necessary elements.

2. Base the design of enclosure on the size and measurements of active components.

3. Draw small cavity (for LDR) underneath clear material used for interactive elements.

4. Simple layer three structure recommended:

a. Top layer for exposing light emitting components (LEDs) for display and

housing optically clear material for interaction.

b. Middle layer for exposing light intensity receiver (LDR).

c. Bottom layer for support of active components.

5. Draw four holes for each corner of each layer which correspond with each other for

nuts and ballots to hold entire enclosure in place securely. This is the easiest design

approach for assembly, reassembly, and replacing components if needed.

1 https://learn.adafruit.com/downloads/pdf/adafruit-neopixel-uberguide.pdf


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6. Prepare laser cutter setting (for LaserPro Spirit GE please see Appendix Table 2)

a. Use higher power and low speed for cuts.

b. Use relatively high power and high speed for etches (for example: labels on

top layer of enclosure).

1. Use black Perspex material for enclosure as ambient light and stray emission from

LEDs is absorbed rather than reflected.

a. Recommended depth of material more than 3mm for robustness.

2. Once each layer of enclosure is cut and etched where appropriate combine each layer

in sequential order on top of each other.

3. Manually insert active components within their designated cavities.

4. Clear optical material should not be embedded into the enclosure but instead the

enclosure will be used to support a display which is detachable.

5. Once each layer or side of enclosure is cut assembly depending on initial 2D design

a. If holes are used for assembly, use nuts and bolts to hold enclosure object

structure firmly in place corresponding width of holes.

b. If finger edge joints are used it is recommended to apply acrylic adhesive for

best results and hold structure firmly in place.

c. Clear super glue could also work well.

6.3 DESIGN AND FABRICATION OF DISPLAY The display is considered to be a separate element of the device which can be inserted on top

of the enclosure where cavities for the display’s LEDs are positioned. The display can be

scaled up or down depending on the needs and specifications.

1. Draw outline of display 2D vector based design software (such as Illustrator).

2. Draw segmented design that corresponds to the number of LEDs.

a. Use full colour fill for areas of display which are to be illuminated – these will

be etched – recommended for etching is crisscross pattern as light rays are

distributed more evenly throughout all of the section without illuminating the

direct path of light source - Each section of display which is to be visualised

individually.

3. Draw lines of no more than 0.72mm.

a. The minimum thickness of the blocking material is limited by its material

properties. Specifically it was observed that even black opaque Perspex

behaves like a translucent material when cut into thin slivers (<0.72mm thick)

4. Each path of cut should isolate an individual section of the display.

1. Optically clear Perspex material (depth no more than 1mm – for robustness).

2. Cut and etched transparent material using 2D vector design.

3. Cut inserts corresponding to cuts made in display from black material of same depth.

4. Manually situate black material inserts into clear display.


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5. Secure structure with clear adhesive if necessary. Aim to use as little as possible so as

not to disrupt reflective properties of any edges.

6.4 PROGRAMME DISPLAY Each light-emitting diode (LED) must be designated to a single segment (see Figure 6.1). It is

not necessary to use multi-coloured LEDs. However, colour changing visualisations provide

an extra dimension of clarity when displaying sequential information using just one SSD.

Figure 6.1: To display numeric figure “3” LEDs 3, 4, 5, 6, and 7 must be active

whilst LEDs 1 and 2 must be inactive.

Multi coloured LEDs are activated and set colour using three input variables – red, green, and

blue (RGB). Figure 6.2 shows basic sequence of active and inactive states of each LED to

display numeric figure “3” in green. An Arduino Adafruit NeoPixel library function is used

for controlling single-wire-based LED pixels and strips of LEDs.

Figure 6.2: Example Arduino processing code for visualising numeric figure “3”.

// Activate LEDs

pixel_01.setPixelColor(2, pixel_01.Color(0, 255, 0)); // LED 3

pixel_01.setPixelColor(3, pixel_01.Color(0, 40, 0)); // LED 4 less luminance for consistency




// Inactive LEDs

pixel_01.setPixelColor(0, pixel_01.Color(0,0,0)); // LED 1

pixel_01.setPixelColor(1, pixel_01.Color(0,0, 0)); // LED 2


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6.5 PROGRAMME INTERACTIVE ELEMENT 1. Take sample of light intensity when no pressure or contact is applied to surface of

clear material

a. Find average of at least 500 samples to eliminate chance of anomalies

b. Use average as threshold when no user input is present

2. Take sample of light intensity when low pressure contact is applied to surface of

material

a. Find average of at least 500 samples to eliminate chance of anomalies

b. Use average as threshold for first user input variable

3. Take sample of light intensity when high pressure contact is applied to surface of

material

a. Find average of at least 500 samples eliminate chance of anomalies

b. Use average as threshold for second user input variable

6.6 DISCUSSION AND SUMMARY The main aim of this project was to contribute an alternative approach to designing and

fabricating interfaces with interactive capabilities. Based on initial explorations of light

properties a simplistic method of designing and producing interactive elements and visuals

displays has emerged. By integrating active comments a fully functioning watch prototype

was implemented.

The process described in this chapter outlines fundamental techniques for designing and

developing such active components that can be customised and altered to an individual’s

needs and specifications. Laser cutting enables a low cost and accessible method of

fabricating rapid prototypes. As a result a rapid process of exploring design decisions without

the need to wait for creating a whole new object has emerged.

Electronic components and material used throughout this project are low cost and easily

implemented without need for low level techniques skills. And design space demonstrated

within this project can be elevated further by exploring with a large scope of interactive

interface applications. The process described enables a creative approach to the design and

fabrication of interfaces that could be implemented by a large range of users who do not have

access to high cost optical 3D printers or poses high level 3D modelling knowledge. Design

space could be further extended to 3D curved displays with the use of light pipes of different

depths.

The main limitation of the current system is that user input threshold light intensity must be

calibrated manually when ambient light intensity within the environment changes. The

stability of interactive devices fabricated using the process presented is limited if constant

resets are needed to calculate user input threshold. An algorithm could be implemented to

eliminate ambient light data from LDR readings. Alternatively, a capacitor could be added to

the LDR circuit which would also eliminate ambient light readings. The addition of a

capacitor however, would mean an extra electronic component is added to the fabrication

process.


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In an attempt to capture how the general public would react to the novel interfaces developed

the prototypes were demonstrated in three consecutive sessions. In the wild observations

were written down based on unpremeditated feedback in an attempt to understand how

people respond to new forms of novel interfaces with interactive capabilities. Figure 6.3

comprises of words and phrases frequently mentioned when demonstrating prototypes

produced from this project across three consecutive sessions.

Figure 6.3: Word cloud of key phrases and words taken from observations conducting during open day demonstrations.

Overall the unstructured feedback received from the general public was positive. Greater

interest was shows in the visual aspects on the prototypes demonstrated. This was mainly due

to the bright colours and high luminosity emitted that attracted higher interest. A number of

suggestions for possible application of this technology were suggested such as car windscreen

clocks and window displays. There was also excitement at the concept of implementing such

interfaces in social night club environments.

Each of the steps demonstrate the design and fabrication of individual components can be

integrated in create an interface display with interactive capabilities. The watch prototype

described and implemented shows that functioning interactive interfaces could be produced

with a limited number of active components using laser cutting techniques. The conclusion

chapter revisit objectives declared at the start of this report and analyse the solution outlined

throughout this project. Current limitations and future work is also discussed.


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7. CONCLUSION

This project demonstrated an alternative approach for rapid prototyping of novel interactive

interfaces. Using low cost and highly accessible optically clear Perspex material and adding

interactivity using basic light receiver sensor and light emitter. The design considerations for

this process should enable replication of similar devices. Extending this, alternative novel

approaches to interface implementation could also be explored by following the five inclusive

steps described previously.

The use of a laser cutter enables rapid fabrication of prototypes without the need of high level

knowledge of 3D modelling. Perspex material used for this project can be easily obtained at

low cost and offers higher quality finish compared to resin, Acrylonitrile Butadiene Styrene

(ABS), or Polylactic Acid (PLA) used for 3D printing.

7.1 REVIEW OF AIMS The initial aims of project have been successfully met. A general approach was presented for

using laser cut Perspex prototype elements to display information and sense user input.

Techniques for visualising information using laser cut optically clear material, including use

of etchings and cuts to enhance luminosity of displays can be demonstrated by the

implementation of three varieties of seven-segment displays. Techniques for sensing user

input with laser cut transparent material were demonstrated through the application of a

button light switch and accelerometer. This involved touch pressure input with an embedded

sensor and manual displacement of light wave guides. An example application watch

prototype demonstrated how laser cut optically clear material could be implemented to

fabricate a wearable interactive display.

7.2 LIMITATIONS In depth explorations of light studies should be conducted to ensure a more developed

understanding of light properties of optically clear Perspex plastic. Smaller LEDs for

visualisation and interactive purposes could be used to further scale down size of devices

fabricated. Refinement of etching style on the surface of the material could also enhance

valuation of information displayed. A varied range of applications should be designed and

tested to uncover limitations of laser cutting interactive prototypes. Only flat displays were

fabricated and this limits current knowledge of possible implementations of curved and 3D

surface displays.

Optical properties of materials other than Perspex should also be explored in order to extend

current findings from this project to a larger scope. When ambient light is present certain

segments are occluded by others and do not illuminate as prominently. Further explorations

of interface design must be made to enable enhanced visualisations of information without

any inconsistencies. The laser cutter used throughout this project also varied in quality and

precision of cuts and etches due to maintenance issues. As a result laser induced damage to

the material decreased quality of optical illumination.


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7.3 FUTURE WORK Although the original aims of this project have been met, further refinements and extensions

of studies can be implemented in the future. Implementation of alternative interface designs

with curved surfaces and extrusions would contribute to current fabrication process available

in the field. Extending light studies by exploring effects of light intensity in a range of widths

and scales of material would build upon current understanding of optical light properties of

Perspex.

Algorithmic implementations of interface designs should also be considered in future work.

A 2D vector design system could be developed where users draw their interface segments

have black insert cuts algorithmically generated. With reference to Aurenhammer [1]

Voronoi diagrams geometric paths could be computed in order to isolate each segment based

on the nearest neighbour concept as seen in Figure 7.1. This would reduce the need for a user

to manually design black insert cuts for an interface.

Figure 7.1: Voronoi diagram isolating each of the eight points with maximum space around each centre.

7.4 LEARNING OUTCOMES Throughout the duration of this project a range of skills and knowledge was obtained. I have

encountered new forms of prototype fabrication with the support of Computer Aided Design

(CAD). I now have proficient knowledge of operating a laser cutter for a wide range of

applications. My knowledge of electronics and circuit board implementations has enabled me

to not just design devices but also produce rapid high fidelity prototypes efficiently. My

Arduino programming skills have greatly aided the progress of this project and have been

further enhanced through the range of applications used such as conducting lighting studies

and visualising meaningful information using just seven LEDs. This project enabled me to

explore new possibilities for interactive interfaces and sensors using simple laser cutting

techniques. Overall the process derived from this project successfully enables a novel

approach to fabricating interactive interfaces and sensors using simple laser cutting

techniques and two electronic components (light source and light sensor).


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BIBLIOGRAPHY

[1] Aurenhammer F. (1991) Voronoi diagrams—a survey of a fundamental geometric data structure.

ACM Computing Surveys (CSUR), 23(3), 345-405.

[2] Baudisch P., Becker T. & Rudeck F. (2010, April). Lumino: tangible blocks for tabletop

computers based on glass fiber bundles. In Proceedings of the SIGCHI Conference on Human Factors

in Computing Systems (pp. 1165-1174). ACM.

[3] Bergman D. J. and Stockman M. I. (2003) Surface plasmon amplification by stimulated emission

of radiation: quantum generation of coherent surface plasmons in nanosystems. Physical review

letters, 90(2), 027402.

[4] Blöchl P. E. (1994) Projector augmented-wave method. Physical Review B,50(24), 17953.

[5] Brockmeyer E., Poupyrev I. & Hudson S. (2013) PAPILLON: Designing Curved Display Surfaces

With Printed Optics for USIT (2013).

[6] Han J. Y. (2005). Low-cost multi-touch sensing through frustrated total internal reflection. In

Proceedings of the 18th annual ACM symposium on User interface software and technology (pp. 115-

118). ACM.

[7] Han J. Y. (2008) U.S. Patent No. 20,080,284,925. Washington, DC: U.S. Patent and Trademark

Office.

[8] Lin R. (2003) U.S. Patent No. D469,089. Washington, DC: U.S. Patent and Trademark Office.

[9] Mader A., Dertien E. & Reidsma D. (2012) Single value devices: In Intelligent Technologies for

Interactive Entertainment (pp. 38-47). Springer Berlin Heidelberg.

[10] Mueller S., Kruck B. & Baudisch P. (2013) LaserOrigami: laser-cutting 3D objects. In

Proceedings of the SIGCHI Conference on Human Factors in Computing Systems (pp. 2585-2592).

ACM.

[11] Orchard A. R. (1993) U.S. Patent No. D337,104. Washington, DC: U.S. Patent and Trademark

Office.

[12] Rümelin S., Beyer G., Hennecke F., Tabard A. & Butz A. (2012) Towards a Design Space for

Non-Flat Interactive Displays. In ITS (2012)

[13] Savage V., Schmidt R., Grossman T., Fitzmaurice G. & Hartmann B. (2014) A Series of Tubes:

Adding Interactivity to 3D Prints Using Internal Pipes For UIST (2014)

[14] Suman M. J., Welling T. L. & Schneider R. J. (1998) U.S. Patent No. 5,822,023. Washington,

DC: U.S. Patent and Trademark Office.

[15] Takada Y., Kanagawa K., Nakabayashi R. & Kanagawa K. (2012) Ficon: a Touch-capable

Tangible 3D Display using Optical Fiber. In ITS (2012)

[16] Wills K., Brockmeyer E., Hudson S. & Poupyrev I. (2012) Printed Optics: 3D Printing of

Embedded Optical Elements for Interactive Devices for UIST (2012)


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APPENDICES

PROTOTYPE ELEMENTS

Appendix Figure 1: Button light switch enclosure design outline.

Appendix Figure 2: Accelerometer enclosure outline.


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SEVEN-SEGMENT DISPLAY CHAPTER

Appendix Figure 3: Enclosure for initial SSD with cavities for LEDs to be situated on all four sides of the display.

Appendix Figure 4: Enclosure for second SSD with cavities for LEDs to be situated only on the bottom of the display.


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Appendix Table 1: Visual observational findings from initial SSD design explorations with power and speed used.

Test # Etch/Cut Speed Power PPI Material

Depth

Etching

Type

LED

BirghtnessImage Result Result Comments

1 Etch 60 70 500 3mm Matt 100

Real Life: Etched edges closest to LEDs

are brightest - can see direction of light

rays on fully matt etched surface

panning out - middle segment not

obvious - very hard to differentiate

between segments which are intended

to be on and off

Photo Result: Illumination of segments

more prominent compared to real life -

light does not fill whole segment - issue

with illuminating middle segment -

Need guide and manipulate light waves

2 Etch 60 40 625 3mm Dots 100 Same as Test 3 but without middle cuts

3 Cut (16) 1 75 400 100

4 Etch 60 50 625 3mm Dots 100

Real Life: Display still not obvious

enough - cuts in plastic guide light more

reflection and more illumination -

display is very bright - very hard to make

out any difference

Photo Results: Pretty much the same as

real life

5Cut

(0.01 inch)1 100 1500 100

6 Etch 60 50 625 3mm Matt 100

Real Life: Matt etching works better -

more obvious which segments are

illuminated - could enhance further -

interesting reflection behaviour for

middle section - cuts guide the light

waves efficiently - the middle segment

is illuminated more obviously

Photo Results: Contrast is more

emphasised due to white balance in the

camera - effect of illumination more

prominent

7Cut

(0.01 inch)1 100 1500 Dots 100

Same as Test 3

8 Etch 70 50 625 3mmMatt/

Dots100

Real Life: Outside section illuminated

more prominently - middle section not

as much - display overall very bright -

need less light by having less cuts?

Photo Results: middle section much

better shown in photo than in real life


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Appendix Figure 5: Single layer SSD display were LEDs are situated at the bottom.

Speed Power PPI

Etch 80 90 1000

Cuts 0.7 100 1500 Appendix Table 2: Most effective setting for cutting and etching Perspex Material (5mm depth) for SSD display


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WATCH CHAPTER

Appendix Figure 6: Watch prototype LED enclosure laser cutter design with cavities on top side for LEDs.

Appendix Figure7: Final watch display laser cut design.

Appendix Figure 8: Button for watch laser cut design.


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PROJECT PROPOSAL

Illuminative interactive interfaces are becoming more prominent as the manipulation of

optics2 is becoming an integral part of sensing, display and illumination of interactive

devices. This project proposes a design model which enables the development of various

novel interfaces with emphasis on using an easily accessible medium of Perspex sheets and

laser-cutting. One of the main aims of this project is exploring the relationship between light

waveguides using frustrated total internal reflection (FTIR3) and by laser-cutting Perspex to

desired specifications. As a result of the lighting experiments, the project aims to generate an

accessible design model which end-users are able to adopt with ease and flexibility to

construct interfaces for particular needs. Understanding the relationships involved with laser-

cutting reflective behaviour and diffusive properties of light interaction with etched surfaces,

all account towards establishing a primary model that end-users are able to understand and

implement.

This project aims to design and implement a variety of novel interfaces through modelling

light waveguides and constructing them via laser-cutting and etching with capabilities of

direct user input via touch sensing. Establishing principles for a design model is the main

focus of the project. End-users, who wish to create novel illuminative interfaces via laser

cutting and etching, can also implement their ideas with ease via the developing design

model. This report covers the background of how novel interfaces are created using

manipulated optics, frustrated total internal reflection, laser cutting techniques and manual

ray tracing. In the background section there is also discussion on how the current research can

be implemented and further developed through this project in order to surpass limitations.

The proposed project section covers details regarding the methods used to develop the

indented novel interfaces and the experimental elements of the study. Specific details of the

main objectives and a breakdown of the phases required to complete the project can be also

be found as well as a Gantt diagram showing the breakdown of tasks. Required resources are

also listed as well as references used for this report.

2 + 3 Printed Optics: 3D Printing of Embedded Optical Elements for Interactive Devices

- Karl D.D. Willis - Eric Brockmeyer - Scott E. Hudson - Ivan Poupyrev 3 Frustrated Total Internal Reflection: A demonstration and review -

http://www.cleyet.org/Misc._Physics/Microwave-Optics/Evanescent-FTIR/FTIR%20review.pdf 15/05/2014


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With recent innovation in optical quality 3D printing, it is now possible to construct novel

interfaces designed for specific needs and purposes. There is now emphasis on creating

devices that can be modelled as a single object without the need to have individual circuit

boards and assembly parts. 3D Printed Optics4 now allows for rapid prototyping of interactive

devices with fabrication techniques such as Sensing Displacement embedded within devices

during their creation. Sensing Displacement is a fabrication technique that uses an infrared

emitter that releases light rays through a transparent material (Perspex for instance) which

can be recorded by an infrared receiver. The IR receiver is able to register high or low

readings and from these can determine if there has been any physical interaction made on the

surface of the device. 3D printing is predominantly a high cost technique that is rarely

accessible to most people whereas the proposed use of laser-cutting and etching would

produce the desired effect at a lower cost and in less time.

Sauron5 is an embedded single-camera sensing for printing physical user interfaces that aids

designers in developing prototypes that are ready action objects. With minimum assembly

and wiring, Sauron assists designers in creating rapid prototypes that are interactive from the

start. With inspiration from Sauron’s system this project also aims to develop a model that

can relate to principles of rapid prototyping of active objects by deriving possible interactive

elements of devices early on in the design process.

As this project will entail the use of laser-cutting as opposed to 3D printing, which is more

expensive in monetary terms, it is key to explore different possibilities for using the laser

cutter. A concept inspired by research Stefanie Mueller into LaserOrigami6 can prove to be

an aid when designing and assembling novel interactive devices for this project.

LaserOrigami is a rapid prototyping system that produces a 3D object via a laser cutter, this is

a much faster fabrication technique compared with 3D printing and even standard laser-

cutting as there is no manual assembly. Although the prototypes created through

LaserOrigami are static objects, the techniques for fabrication can aid the design and

assembly of devices for this project.

Frustrated Total Internal Reflection was first developed for interactive multi-touch tables by

Jeff Hans7 . As light enters the core of a transparent material the ray is reflected through the

core if the wave strikes a medium boundary at an angle larger than that of the angle of the

surface boundary.

5 Sauron: Embedded Single-Camera Sensing of Printed Physical User Interfaces - Valkyrie Savage, Colin

Chang, Bjorn Hartmann - 2013 6 LaserOrigami: Laser-Cutting 3D Objects - Stefanie Mueller, Bastian Kruck, and Patrick Baudisch - 2013 7 Low-Cost Multi-Touch Sensing through Frustrated Total Internal Reflection – Han, J. Y 2005 (In Proceedings

of the 18th Annual ACM Symposium on User Interface Software and Technology)


Page 62 of 68

As shown in Figure 1 any interaction/frustration

with the outside of the surface causes light rays

within the core to escape from the boundaries

into the air. This project will adapt FTIR to

different technologies, such as wearable

devices, instead of just interactive tables.

The main aim of this project is to develop novel displays with input capabilities through

laser-cutting Perspex plastic to construct and model light waveguides. This project will focus

on using laser-cutting and Perspex plastic as opposed to 3D printing as it is considered to be

more accessible to most people. With the fabrication of successful novel interfaces complete,

it will also be beneficial to explore how end-users would be able to implement their own

ideas via laser-cutting and etching in an efficient and affordable way.

By exploring and understanding patterns from lighting experiments conducted at the start of

this project a variety of prototypes with input functionality will be developed. Each

successful prototype will be evaluated and compared against one another in order to establish

a model of design patterns that can be implemented for specific requirements and this will

result in a design model represented via an infographic.

Light

Experiments

List of Behaviours

and Patterns

Design Model

(Infographic)

Prototypes

Prototype

1

Prototype

2

Prototype

3

Project

Report

This diagram represents the workflow

of this project

Diagram of a finger touch that is used to frustrate

the light waveguide – FTIR

*Taken from: http://cs.nyu.edu/~jhan/ftirsense/


Page 63 of 68

These novel displays will be constructed by laser-cutting and etching Perspex plastic sheets

and applying LED lights to one end of the cut transparent plastic, modelling specific light

waveguides that can manipulate photons to illuminate particular areas when needed to display

graphics. The user will be able to touch the surface of the plastic directly. This in turn will

disturb the light rays and cause them to scatter outside of the core of the Perspex. This change

in the light ray behaviour (intensity/direction/destination) can be used as an input variable for

interaction detection.

The project will involve two main phases. Beginning with experimenting and establishing

behavioural patterns of visible light interacting with Perspex via ray-tracing and manipulating

FTIR8 elements, a model of similar patterns can be observed. This design model will form

principles that shall aid the creation of prototypes in the second phase of this project. An

optional additional third phase can be implemented for user evaluation and focus group

testing on the design model.

Activity 1 - The familiarisation of laser cutter in order produce quality laser cut objects.

Explore different laser cuts and etching techniques to establish the core foundation for the

project.

Activity 2 - Understand how light rays can be manipulated to produce a desired result of

specified illumination. This is one of the key aims of this project. By using etching to defuse

reflections and laser-cutting to construct pathways for reflection and refraction, this project

will explore how laser-cutting Perspex in particular ways can affect light intensity and

illumination. The recorded results of this activity should produce a list of behaviours and

their characteristics.

Activity 3 – Deliver interaction using Frustrated Total Internal Reflection (FTIR), where the

scattered light ray readings recorded by the IR receiver can be used to manipulate the

interface by changing the paths of light rays traveling through the core of the Perspex. A

small Arduino can record the input transmitted by the IR receiver or even a Light Dependent

Resistor (LDR) and visualise the results.

Activity 4 - Generate an infographic/diagram representing the patterns and relationships

found between etchings, laser-cutting and light intensity. This will inform the development of

prototypes in phase two.

8 http://wiki.nuigroup.com/FTIR


Page 64 of 68

The second phase of the project will involve creating functional prototypes.

Activity 5 - Establish templates for a functional set of prototypes which correspond to

patterns found in the lighting experiments conducted in phase one.

Activity 6 - Create prototype one.

Activity 7 - Create prototype two.

Activity 8 - Create prototype three.

Activity 9 - This is the final activity of the project and will conclude with a written report of

all findings gathered from this project.

The novel interfaces will include touch sensitive wearable

technology such as a bracelet (Figure 3), which could

implement multiple input capabilities9 10

. This will be done by

using Frustrated Total Internal Reflection (FTIR) to

manipulate light waveguides to avoid occlusion as the light

source would be at the back of the bracelet while the

illuminations will occur at the front, where the user is able to

view the display.

In addition to this example, an interactive keyboard may also

be developed by modelling light waveguides to specifications

and using a “planar waveguide11

” system made from Perspex

that is laser cut and etched. This illuminative keyboard will be

capable of display a QWERTY style keystroke layout with

input and output functionality through the frustration of light

rays trapped within the “core” of the Perspex.

These are just two examples of possible interfaces that can be

developed using simple Perspex material and laser-cutting.

The 3rd

prototype developed for this project will take into

account a variety of possible interactive displays that can be created.

9http://www.prnewswire.com/news-releases/interactive-led-wristbands-are-lighting-up-shows-and-events-

258647261.html 17/05/2014 10http://www.ecouterre.com/the-dial-is-an-illuminated-rotary-phone-for-your-wrist/dial-phone-bracelet-2/

17/05/214 11 http://electron6.phys.utk.edu/light/10/light_guides.htm 15/05/2014

Possible design for an interactive

bracelet


Page 65 of 68

This phase is only feasible after the project has secured successful results from the first two

phases and there is still time to implement additional work for this phase. This 3rd

phase will

involve implementing a framework system, which can be presented to a focus group. The

focus group will be able to evaluate the system and their feedback will establish key

principles of how end-users intend to develop their own ideas into specific novel interfaces.

A design workshop will uncover the functional and non-functional requirements of such a

modelling system through a focus group review.

Illuminative interfaces have the potential to stimulate the users both visually and physically,

but they lack a design model which would aid their construction. As a solution to this

problem, this project aims to generate a series of tests that explore the manipulation of light

waveguides, light reflection and refraction within the core of Perspex plastic. Exploring how

Frustrated Total Internal Reflection (FTIR) can be best implemented in order to allow the use

of the Perspex surface as an input mechanism.

Although many interactive object oriented interfaces employ the use of 3D printing as their

primary tool, 3D printing is still highly inaccessible and expensive for public use. Perspex

plastic is more accessible and cheaper in terms of size compared to 3D printer filament and

resin (for gluing). A laser cutter can implement the same geometric properties to a shape as a

3D printer but a lot faster also. It is clear that the use of laser-cutting and Perspex material is

more cost efficient compared with 3D printing as well as easier for end-users to create their

visions via laser cutting.


Page 66 of 68

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Page 67 of 68

1. Access to Illustrator and other vector based software for design of interfaces

2. Prototype modelling via 3D software such as AutoDesk Inventor

3. Access to laser cutter

4. Electrical components needed include:

o Arduino – For control and readings

o LED lights (IR emitters)

o IR receivers

o Light Dependent Resistors (LDR)

Papers:

Printed Optics

Printed Optics: 3D Printing of Embedded Optical Elements for Interactive Devices by Karl

D.D. Willis, Eric Brockmeyer, Scott E. Hudson and Ivan Poupyrev – 2013

Frustrated Total Internal Reflection (FTIR)

Frustrated Total Internal Reflection: A demonstration and review by S. Zhu, A. W

Yu, D. Hawley, and R. Roy – 1985

Low-Cost Multi-Touch Sensing through Frustrated Total Internal Reflection

by Han, J. Y - 2005 (In Proceedings of the 18th Annual ACM Symposium on User

Interface Software and Technology)

Sauron

Sauron: Embedded Single-Camera Sensing of Printed Physical User Interfaces by

Valkyrie Savage, Colin Chang and Bjorn Hartmann – 2013

LaserOrigami

LaserOrigami: Laser-Cutting 3D Objects by Stefanie Mueller, Bastian Kruck, and

Patrick Baudisch – 2013

Websites:

Light Waveguides

http://electron6.phys.utk.edu/light/10/light_guides.htm

Sourced - 15/05/2014

Frustrated Total Internal Reflection (FTIR)

http://cs.nyu.edu/~jhan/ftirsense/

Sourced - 15/05/2014

http://wiki.nuigroup.com/FTIR

Sourced - 18/05/2014


Page 68 of 68

Prototype Concepts Inspiration

http://www.prnewswire.com/news-releases/interactive-led-wristbands-are-lighting-up-shows-

and-events-258647261.html

Sourced - 17/05/2014

http://www.ecouterre.com/the-dial-is-an-illuminated-rotary-phone-for-your-wrist/dial-

phone-bracelet-2/

Sourced - 17/05/2014

LaserOrigami

http://stefaniemueller.org/

Sourced – 17/05/2014

Download - Aluna Everitt A Novel Approach to Interface …...Aluna Everitt A Novel Approach to Interface Fabrication Using Laser Cut Optically Clear Perspex B.Sc. (Hons) Information Technology

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