D&T Electronics and Control Systems

By Harry Holmes

The theme of the project is generally based upon “Security,” and to evaluate different alternatives and forms of security. The spider diagram displays security related products. I have chosen the theme security as the primary theme because by exploring different categories of security product, effectively I can choose the most appropriate product that delivers the what it’s intended purposes are. In this case offering protection, hopefully the developed product will be able to offer some sense of security.

Security

Personal Protection

Householdand Property

Safety

Feeling Secure

Vibration sensor

bicycle lights

Night Light

Door Alarm

Fire alarm

Water temperture sensor

Food Temperture

Garden lights

Security lights

Sound alarms

Notification lights

Temperture Indicator

Sound Sensor

Rape Alarm

Attack Alarm

Fridge door indicater

Light Sensor

Room temperture indicator

Flood Alarm

Idea or Topic

Medical Security

Heartbeat Monitor

Temperture Sensor

Motion Sensor

Carbon Monoxide Sensor

Pressure switch Alarms

USER NEEDS

WhyThe purpose of security produces are to certify the consumer of protection or promoting the sense of security. Subsequently preventing crimes of theft and burglary.

WhoThe product will generally be used for protecting items and possessions against prospects of burglary. As a result presenting a level of reassurance towards homeowners.

WhereThe pressure alarm will probably be placed at possible points of entrance in the burglar’s perspective, for example windows and doors, furthermore, the entire circuit can be concealed as a doormat therefore it is less suspicious and interfering.

WhatThe circuit will consist of pressure sensors that detect and triggers when an application of pressure is identified, possibly containing a time delay otherwise any form of contact will trigger the alarm, putting into mind its practicality.

When During a robbery, a burglar might try to enter the premises. In this situation if the house is secured then it will most likely be a trigger an alarm and potentially prevent further intrusion. Equally, if the house is insecure than there are no obstructions restricting the burglar’s attempts to steal.

According to statistics from the British Crime Survey (BCS) Burglaries in England and Wales have increased by 14%. Recent survey on 45 000 households have also shown that crime rates has escalated slightly.

Questionnaire

Question YES NO1)Are your house and contents insured? ||||| |||| (9) ||||| | (6)

2) Do you think using a pressure switch in the alarm system is practical? ||||| ||||| (10)

||||| (5)

3) Should the product be sustainable? ||||| ||||| ||| (13) || (2)

4) Do you have any neighbours? ||||| ||||| |||| (14) | (1)

5) Do you express a need for it? ||||| ||||| (10) ||||| (5)

6) Should it be portable? ||||| ||||| | (11) |||| (4)Conclusion

The questionnaire and the market trend of similar products will be used to determine the product’s specification. 1) The majority of people said that their houses are insured therefore there may be less need for a burglar alarm however, 20% of people said that

they weren’t insured. As a result there may also be a need for burglar alarms.2) The question asks whether using pressure switches in an alarm is practical, two-thirds of people said yes. So it would probably be sensible to add

pressure sensors in my circuit.3) Most people decided that the product should be sustainable, in order to achieve sustainability products will need to use less energy and

resources. Such as using renewable energy, recyclable materials, changes to the manufacturing process, etc… 4) Almost everyone said that they had neighbours, in this case alarms with sound would be more effective because burglars will feel more

uncomfortable breaking into a neighbourhood as opposed to an isolated house. Consequently a siren will have a greater chance of deterring the intruder as the sound of a siren may alert the people in the area.. Which also means that a time restriction should be fitted in the circuit, this is because the sound of an alarm may disturb people in the area.

5) Although most of the homes are insured two-thirds said that they expresses a need for an alarm. This may be because irreplaceable items such as photo albums cannot be compensated. So there is a need for burglar alarms despite most houses being insured.

6) Most people said that it should be portable. The obvious choice would be batteries, however there is also a requirement for the product to be sustainable. Using batteries may harm the environment if it is not properly disposed. For that reason we could use rechargeable batteries.

Questionnaire Result (Qualitative Data 1)

Question Sound Light Other alternatives

What output do you suggest is the most effective?

||||| ||| (8) || (2) |||| (Light and Sound, 4)| (Mechanical, 1)

Question Battery Plug Others

What category of power source do you suggest the product operate on?

||||| |||| (9) |||| (4) || (Solar powered, 2)

I have chosen sound as the output of my circuit because it was selected by the most amount of people. Also because light is simply too hard to detect especially when someone is asleep. Some suggested sound and light, but if you were close enough to see the light being activated then surely you will also be able to sense the sound. For that reason I don’t think two separate outputs (light and sound) will need to be combined.

Most people chose batteries when asked what power source they wish the circuit should operate on. Nonetheless plugs can also allow the circuit to be portable. Furthermore it is much more sustainable than disposable batteries, and also more reliable because you won’t have to worry about whether the batteries have run out or not. Thus excluding the need of a power indicator, resulting in less resources used and reduces the cost and energy of the manufacturing process. Which is being sustainable and environmentally aware. Meanwhile, solar powered alarms may be expensive to make and therefore expensive to buy. Solar powered devices only work when there is enough light, however the alarm will be placed indoors. On the other hand there might not be a plug socket near the entrance of the building, so the alarm may not be as effective. If there are no plug sockets then it could use cables, however those cables will also need to be manufactured. Additionally it may interfere with everyday lives. So I have chosen to use batteries to power my circuit.

Questionnaire Result (Qualitative Data 2)

Question £15 or less £15-£20 £21-£30 £30-40 £40 or over

How much are you willing to pay for a security device? ||| (3) || (2) ||||| | (6) ||| (3) | (1)

Question 2-3 4 5 6 or more

How many times a week is your house unoccupied? ||

(2)|| (2)

||| (3) ||||| ||| (8)

Questionnaire Result (Quantitative Data)

The price that was chosen the most was £21-£30, this shows that my product will need to be below £21 in order to make a profit but also match the buyer’s expectations. Because most have gone for the intermediate price range, so the alarm will need to be more complex than a simple circuit meanwhile not above the cost of £21. If there is a need for alarms, (which there is because two-thirds of people said that they expressed a need for an alarm) then maybe people will be prepared to pay £30 for a household alarm. So the product could be made with better quality materials or with improvements to the circuit.

To find whether there is actually a need for a circuit alarm I asked a more subtle question ,“How many times a week is your house unoccupied.” I thought that it was an important question because in question 5 which asks whether people expressed a need for an alarm, most people said yes. But this could be because the alarm gives an added sense of security. So why not just build a circuit where there’s only a flashing LED? Which saves expenses and resources . By asking this question, it identified that there is a genuine need for an alarm because most people leave the house unoccupied for 6 or more time a week. So there is a need for a proper alarm that can actually deter a burglar once that person once entered the house, not just to reassure people. Since there are a lot of times a house is unoccupied, it would be wise to have the alarm on at all times. So using rechargeable batteries are probably a good idea.

Product Cost Typical user

When / Where used? Function

Technology used

(Input / Output) Manufacturing process used

 

LED garden light

£15.99It is intended for use in gardens throughout the night in order to detect any movements.

It automatically turns on at night using a light detector, however, it can only provide black and white picture in darkness.

Input: Light level

Output: Light---------------------

 

Honeywell

Alarm Panel

£32Individuals who owns

properties they intend to protect e.g. property or possessions.

Prevents unauthorised personnel’s entering the

premises, unless they acquire the necessary code. (Requires correct combination to disarm.

Continuous input error will result upon the activation of

siren.

Input:. Push button combinations

Output: External Sirens emitting sound

---------------------

Honeywell

Security Camera

£218.29Captures video evidence of the

criminal, to provide enough evidence to identify the person.

Surveys the area where it is positioned. Although it doesn’t

really do anything that’s noticeable (It has no sound or

light outputs) the security camera can also provide a sense

of security and can also discourage burglars from

entering.

Input: manual switch

Output: Motion detection and video surveillance

----------------------

LED garden light - Amazon The product is a garden light equipped with 30 separate LED lights. It draws its power through the plug socket. The recording camera is capable of recording coloured images during daytime and records black and white images at night. The 380 resolution camera requires a 12V power supply. Its manufactures are “BV&Jo”

Alarm Panel - It has a built in tamper control in order to prevent any unauthorised modifications. There are also 2 variations of keypad LCD and LED. The LCD keypad is capable of supporting 250 event records such as the time and date of interactions with the panel, where as the LED holds 8 event memory. Its battery capacity is 2.4Ah. The manufacturer of this product is “Honeywell.”

Surveillance Camera - The security camera records images up to 550 TV Lines or More. The camera also blocks strong light sources improving its overall video quality and prevents burglars from disabling the camera by shining a bright light. It requires a AC 24V ±10% /DC 12V power source and it’s power consumption is approximately 3W. The manufacturer is “Honeywell.”

Through researching 3 similar products on the market I found out that most would not interfere with everyday lives. However it isn’t so simple when using a pressure alarm because it will not recognise whether the owner has stepped on it or if it’s the burglar. Therefore it will still be triggered regardless of who stepped on it in the first place. To solve this problem I’ve decide to place a SPST switch near the power source so that it can be manually turned off. Since the pressure sensors can be concealed under a mat so anyone could step over the sensors without triggering the alarm.

Product Analyses and Summary

Product 1 (Complex)

Product 2 (Simple)

Function Wireless pressure sensor, detects signals from a pressure circuit which is then transferred to a sound emitting device.

Pressure mat connected to a sound emitting device.

User need fulfilled

Yes, as it is able to detect pressure and notifies you when it has. Yes, however, it is not as discrete as the wireless sensor.

MaterialsUsed in

construction

Plastic, stainless steel, paint coating, and circuitry, and wiring. Textiles, circuitry, wiring, rubber, and plastic

Durability of product

The product is not very durable as it mainly consists of plastic that easily shatters or cracks when dropped.

Same characteristics of Product 1 as they are both made of plastic. Though Product 2 seems more vulnerable as it cannot be stored discreetly so the siren possibly will be mistakenly treaded on.

Sustainability The product itself can be reused, but it requires a supply of batteries. They both require external power sources therefore there is a limit to its sustainability. However the most of the plastic casing are recyclable.

Life cycle The product can be reused by placing new sets of batteries until the product stops working. Judging by its replaceable power source I think it has a moderate period of usability.

The product uses 2 sets of AA Batteries also replaceable when the power supply has been exhausted.

Energy Use 9V PP3 Battery

2xAA

PowerDelay before INPUT

INPUT

Combine

inputs?

Delay after INPUT

PROCESS

Delay after OUTPUT

OUTPUT

Battery 9v Monostables Push to make/to break switch

AND gates

Monostables Transistor Monostables LED

Solar powered

Resistors SPST switch Nand gates

Resistors Darlington pair Resistors Motor

Power cable

Variable resistors

Reed switch OR gates Variable resistors

MOSFET Variable resistors

Buzzer

Capacitors Light dependant resistor

NOR gates

Capacitors Monostable Capacitors Lamp

Thermistor Astable Piezo transducer

Latch switch Comparator Displays

System Diagram

Systems Descriptions

Power source The circuit will be power by two 4.5 v batteries. In total supplying 9 volts.

Process The 555 chip is used in basic timer devices. The mono-stable has 2 states. One of which is stable and the other unstable (transient). Once activated the mono-stable will become “unstable.” After a set amount of time it will then return to its normal “stable” state. This is particularly useful when you’re creating a time period in response to an input. Length of time can be adjusted using the variable resistor.

Input This is an inverted push to make switch. Because I intend to have a pressure switch before the mono-stable. So I need to have a negative output to trigger the mono-stable. Which is why the pressure switch and the resistor have been swapped.

Logic Gate (AND) The AND gate bonds 2 inputs so that you can have 2 separate triggers. The AND gate needs both inputs to be high to turn on the output.

A B Output

OFF ON OFF

OFF OFF OFF

ON ON ON

ON OFF OFF

Process The MOSFET is more sensitive than the Darlington Pair or the transistor because it has a higher gain. When using logic gates in a circuit, it is sensible to use something sensitive to act as a drive.

Output This is a LED, but it requires a negative output to turn it on.

Light Dependant Resistors LEDs are more efficient in the way of producing light compared with incandescent bulbs, because it converts more electric energy into light rather than heat energy. Compared with ordinary bulbs, LEDs also have a longer life expectancy, are smaller, and less easy to break. However, larger LEDs can be more expensive than normal light bulbs.

Input This is an SPST switch, once it has been pushed it makes a closed circuit allowing a current to pass. It needs to be manually re-opened to break the current flow.

Process A buzzer is a device that emits sound. It is often used to notify people of something.

Specification Feature Described Reasons for Feature

Purpose of proposed product

The proposed product will initially emit sound through an buzzer. Essentially broadcast sound when the circuit is actuated as an individual (perhaps an intruder) treads on the pressure switch. However the circuit can serve a secondary purpose of illuminating the nearby area. Which can be especially helpful when you’re trying to find your keys in the dark.

I think it’s integral to incorporate sound emitting functions to both deter the intruder and notify the occupant. Where as the recognised aspects of emitting sound cannot be encompassed through simply emitting light . Therefore I conclude that by emitting sound is more practical as opposed to light where the observer has to be literally within the close proximity of the visible light. Whereas sound is easily detectable and distinctive.

What should the proposed product do

When inputs have been activated, it should firstly turn on a light. Subsequently if the burglar ignores the warning and continues to break in the house then by stepping onto the secondary pressure switch (placed inside the house) will trigger the buzzer (Also placed inside the house)

I think by activating a light before the burglar is within the house is practical because before the burglar has broken the windows or doors in order to gain access, they will have realised that the house is secured with an alarm. Which might discourage the burglar to proceed into the house. Reducing the damage if a burglar visits a house.

What will the proposed product need to sense?

The product will need to sense pressure applied onto the pressure sensor. Then, it will activate a light, then if the burglar remains undeterred and steps on the second pressure switch the siren will produce some sort of sound. Both inputs are pressure switches, so the circuit will need to detect pressure.

I’ve chosen pressure switches because it can be concealed under a matt. Secondly, by combining a pressure switch I can increase the input duration by adding a monostable. So as long as the pressure switch detects a weight it doesn’t matter how long the person steps on it for.

Specification Feature Described Reasons for FeatureWhat will the output need to

be? The output will emanate sound through a siren. There will be a mono-stable to moderate that duration of time in which the siren is activated.

In order to prevent the siren from endlessly emitting sound that may disrupt the surrounding neighbourhood, I have placed a mono-stable. To prevent further disturbances.

What will the power supply be?

The power supply will be supported by batteries.

As opposed to using sockets, batteries can be used internationally and is a portable device.

What voltage should it run on The circuit will run on 9v. In order to prevent damage to circuit components. Furthermore,9v is sustainable by using batteries, therefore not compromising it’s portable property.

Specification Feature Described Reasons for FeatureWill the product have an

on/off switch? Yes, the circuit will have an on/off switch.

I think it’s imperative to have an on/off switch because the circuit can be reset instantly so that you won’t have to wait until the siren has stopped emitting noise. Obviously the sound broadcasted through the siren will be loud so it would be practical for the user to simply reset the circuit when no longer necessary.

Will it have a power indicator? Yes, the power indicator will provide a reading that shows a light if the circuit is both on and has sufficient power to operate.

So that it assures the occupant that the circuit is functional, also to indicate to the viewer that the power supply needs to be renewed when the indicator is off.

How will it be designed? The circuit will be designed on circuit wizard.

The circuit will be designed on circuit wizard because it’s easy to use and the fact that you can incorporate various ideals onto your circuit by placing necessary components virtually means that you can formulate your circuit before making.

Specification Feature Described Reasons for FeatureHow will the circuit be

manufactured? The circuit would comprise of injection moulded casing , circuitry, and soldering components.

Every manufacturing process is integral to the circuit’s capability to function effectively. If not, then the product will not be commercially viable for it’s intended purpose.

How will we ensure that the circuit will be well made and

work?

The circuit will be inspected using Circuit Wizard. As a result, the circuit can be tested through virtual simulations that shows evidence that the circuit is viable, in terms of being functional.

The template “Circuit Wizard” allows the user to design a circuit and also test if the circuit works. Therefore you can test if the circuit works and innovate circuits that follows the guidance given from the questionnaire, market trends and your initial ideas.

INPUTPhase 1: When the Piezo fragment has been displacedthrough movement, it generates minute currents detectable by the Mosfet.

PROCESSPhase 2: The Mosfet then enhances (amplifies) the current initially produced by agitating the Piezo crystal (PZ1) , which in this case is the input that senses vibrations.

PROCESSPhase 3: The current then reaches the 555 timer, indicating that the duration in which the circuit output is active has been lengthened.

OUTPUTPhase 4:The output is a Piezo sounder which releases sound when electricity is applied. However, burglar alarms are less likely to need Piezo sounders because it only needs to product a sound in order to “alarm” the burglar. Therefore a buzzer or siren will suffice.

This circuit could solve the problem though using Piezo crystals which produces a charge depending on how much the crystal is deformed. Therefore does not require additional power sources. However the Piezo crystal can pick up background sound or voltage that may inadvertently trigger the alarm. Furthermore, the piezo crystals are predisposed to cracking when under strain.

POWER SUPPLY/INPUTPhase 1: The power supply is presented as 9v batteries. The pressure switch allows current to pass when pressed.

PROCESSPhase 3: The Darlington pair transmits a “load ” that drives the output. The thyristor “latches” to the circuit when the circuit is activated.

OUTPUTPhase 4: The outputs are the lamp and buzzer which are integrated to emit luminosity and sound. Moreover, producing light and sound as an output was chosen second in favour in the questionnaire; the first being sound.

INPUTPhase 2: Push to make switch moderating current flow.

The circuit has 2 outputs lamp and the buzzer. What emits sound and light, allowing it to be useful at night. However, it is a latched circuit therefore it has to be manually turned off. Which would be more problematic especially as there are no on off switches besides the power supply.

INPUT/OUTPUTPhase 1: An open and close switch that can be manually closed or opened to control the circulation of electricity. Along with a power indicator that displays the state of the power supply.

INPUTPhase 2: Push to make switch substituting a pressure switch PROCESS

Phase 3: The monostables used to extend the duration in which the output is on.

LOGIC/PROCESSPhase 4: The logic gate (AND) incorporates both inputs into the circuit along with a Mosfet to amplify the current. Furthermore, the Mosfet is very sensitive, making it suitable as a burglar alarm because it reacts to the inputs faster than a transistor or Darlington pair.

OUTPUTPhase 5: The buzzer acts as an output, emitting sound in order to frighten and deter the burglar.

This circuit has combined 2 inputs. The first input (a) will be place in the perimeter of the building and the second (b) will be based inside. Primarily because he burglar will recognize that the building is protected as he steps on (a), the light will activate. However I should replace the LED’S with lamps and the buzzer replaced with a siren in order to make the outputs obvious.

a

b

Final circuit Video

* LED substituting a lamp** The buzzer represents the siren

Buzzer acting as a siren.

Both Push to Make switches represents pressure mats.

PCB Format after converting the original circuit design. The LED acting as a power indicator. Which also gives the user a sense of security as it shows that the circuit is operational.

Circuit Evaluation

Problems I stumbled upon some problems when converting my chosen circuit into a PCB. Firstly, because it was too complicated the program was only able to route 83% (at best) of the circuit. This was mainly due to the over-complicated circuit as it had 3 separate chips (2 mono-stable and a logic chip). Furthermore the converted PCB had 6 flying wires (Blue wires as show on the video) along with 7unattached tracks (lines are shown in green). Eventually the components were repositioned connecting all the previously unconnected tracks. However, there were more flying wires and the circuit(s) did not work, the pressure sensor worked but the buzzer did not sound when both pressure switches were triggered (The LEDs shows that the pressure switches was activated). This prompted me to redesign my circuit so that it still had a time delay and 2 separate inputs while cutting back on its complexity.

Video evidence of my circuit not working.

Automatic routing after converting the circuit into a PCB format

Simplified Version of the Circuit

I have also added some resistors which was not included the previous circuit diagram (slide 22). “Circuit Wizard” allows for the some components to be placed without resistors. When running a simulation program, the circuit worked without any difficulties, and meet its designed purpose. However, in reality, the circuit would not have run as smoothly if there was no resistors put in. The LEDS, for example, should be protected with a resistor to prevent it from being damaged or short-circuited.

The main adjustment in this circuit was getting rid of the 555 timer that was placed with input b earlier. The capacitor offers a delay by storing electric energy and releasing it when needed (e.g. pressing the push button switch). The capacitor behaves like a battery, however, it is smaller, quicker to recharge, and releases its energy quicker (less than a second). This makes it appropriate in a burglar alarm as it can recharge quickly in case the burglar returns, and because of its sensitivity, able to respond quickly when the circuit is triggered.

Getting rid of the 555 timer has made the circuit:

- Simpler and therefore easier to manufacture.

- Cost efficient as less materials are used.

- Environmental because there are fewer components. Components that may have harmed the environment during its making.

Resistor to protect LED

The circuit allows the user to adjust the time setting in which the siren is on for, without needing two monostables. The variable resistor (when is set at above135K) will turn itself off just after the capacitor stops producing a current. So in this case input x should turn off after input y. Since it is an AND gate, an input of 0 on any one of its legs will immediately silence the siren. All in all, it gives the user an option to adjust the time setting according to their needs.

Without the monostable in the way, I was able to place the pressure switch directly in line with the capacitor. This save more space when it comes to making the circuit.

b

x

y

aVariable resistor allows user to adjust resistance, and the amount of time input x is positive.

After a successful conversion of the final circuit diagramto its PCB layout, I was only meet with four “rats nests,” which are green wires shown in the image. The green wires show that there are missing routes between the respective components. This problem cannot go unnoticed as a circuit will not work with missing connections. The only way to solve this is to either arrange components so that there is a alternative route for connection, or, to connect a “flying wire,” that links the two points separately, with a cable that crosses over existing routes.

All inputs (all off bard components) have been placed on the right hand side. This makes it easier for others to understand the circuit because people would usually “read” the circuit from left to right. So components should be placed in the order of (from left to right) power, input, process, and output. This would make the circuit neater, and the manufacturing process easier as it gives a faint idea where various components belong. By placing all off board components outside, there is also less risk of wires getting in the way of other components, making it easier to solder other components, furthermore, making it easier when handling the circuit. It also means that wires do not have to be as long. This reduces materials used, creating a more sustainable circuit. Although most unconnected routes have been fixed, one still remain. It would be difficult to get rid of this particular “rat nest” without disturbing other components, and therefore creating more “rats nests” during the process. A flying wire offers a simpler solution, but should always be used as a last resort because it make the circuit untidy.

Flying wire

Picture 1

Picture 2

As there are no more unconnected wires, I can now work on the tracks. Most of the tracks run vertically and horizontally. There needs to be spacing between components so that when it comes to soldering, there is enough room. It also makes the tracks easier to etch.

The PCB has been made smaller by tidying up the tracks. By making it smaller allows the alarm to be concealed, it also saves materials.

PCB Specifications1) Standard Track Width: All track width are to be set at 0.04 inch. Increasing the width of the tracks means that it requires less etching, it also

make the track more resilient. It is common during manufacturing and soldering that the tracks get scratched. A wider track makes is less vulnerable to occasional scratches.

2) Pad size : All round pads should have a 0.12 inch diameter and holes in the centre of the pads should be 0.01 inches in diameter. Larger pads allow more surface molten solder can attach to. This make the component more secure. If too much solder is applied, bigger pads may be able to hold some of the solder so that it does not “spill” onto other pads or tracks.

3) Oval Pad size: Hole sizes for oval pads should also be 0.01. Everything else unchanged. Having a small hole in the centre of pads helps when drilling because it acts as a starter-hole, which can then be made larger to fit different components.

Picture 3

Picture 4

The video is a working example of the circuit. The sirens sounds when both inputs are triggered, it also continues to make a sound, eventually turning itself off. Notice how the red LED stays on after the siren has stopped. This time difference allows the user to adjust the variable resistor so that both inputs are positive for a shorter amount of time. This should reduce the duration the siren in on. However, there is a limit on how much charge the capacitor can hold. So the circuit will turn itself off once the capacitor looses it charge. The time restriction on the capacitor in constant, but the length in which the output is on can be changed. If the user wants to increase the time in which the siren is on, they could simply increase the resistance on the variable resistor so that one input will turn off before the other. But as mentioned earlier, there is a time restraint on the capacitor that cannot be changed. So the circuit will turn itself off eventually.

Testing of PCB

Picture 5

Picture 6

After testing that the PCB works, I removed all the terminal blocks. Terminal block are not crucial in this particular circuit as they are bulky. Terminal blocks like other on-board components need to be directly soldered onto the PCB. Afterwards, a short length of insulation will need to be striped from the wires which connects the terminal blocks with various off-board components. The exposed wires will then be secured onto the blocks by fastening it using a screw. Replacing the connecters with pads will mean less materials used, and possibly saving time and effort. Also, using terminal blocks ensure that wires are protected from conducting materials which may cause damage to the circuit.

Most labels have been removed leaving the ones that show the components value and name tag.

i. 2 Seconds SPST switch is turned on. The power indicator (green LED) lights up.

ii. 3 Seconds Pressure switch 1 is triggered. As a result, the red LED turns on, indicating that input 1 has been activated.

iii. 5 seconds Pressure switch 2 is triggered. As input 1 is also on, the buzzer is turned on.

iv. 11 seconds The buzzer turns off, so does the red LED. However, the input 1continues to supply a current (shown by the glowing LED). Because there’s an AND gate between the inputs and buzzer, it won’t make a difference. The buzzer remains off.

v. 19 seconds The red LED turns off.

PCB board after being etched. The photo shows the underside of the PCB. There are some placed where I will need to take caution when soldering, places where there are exposed copper and PCB.

This photo show me putting on a LED. When attaching components, make sure it is flat on the board so that there are no exposed legs which may be vulnerable to corrosion or being short circuited. To make sure that components lie flat on the PCB:1) Put both legs through the correct holes.2) Once they are through, bend both the

legs so that the component does not fall out.

3) Check if the component is flat on the other side.

4) Secure the entire circuit board onto a clamp.

5) Solder with one hand using the soldering iron and the other supplying solder.

It is practice to label the PCB with the respective values of its components. This makes it easier when it comes to soldering. You no longer have to refer to the circuit diagram when placing components. Furthermore, resistor values in particular should be checked before being placed onto the board. By going through and checking components systematically, it minimises mistakes made while soldering.

Solder groups of components one at a time. All resistors have been soldered onto the board before moving on to different components. The reason for this is because it’s easier to find similar components than to pick out components at random. Also, it gives a chance to practice soldering that particular type of component, so therefore the quality of soldering improves.

The resistance chart shows the values on a resistor based on its color-coding.

The top of my circuit All the resistors have been soldered flat onto the board. All resistance values have been checked, all were correct. The chip socket has also been soldered correctly as there is an upper dent, which faces in the right direction.

Some of the solder joints are slightly tilted, this was because I bent the legs of the component outwards in order to prevent it from falling off while soldering.

Adding too much solder meant that the solder merged itself with another solder joint, making a connection with the neighbouring pad. This connection have to be removed, otherwise it will cause it to short-circuit.

How I solved the problem

I ran the solder in-between the connected pads. This re-melted the solder and I was able to remove the excess solder cleaning. The grey-green smudge left behind can be easily scraped, making the circuit neater.

Are all the components in the correct place? Yes

No

Connect the circuit with an off-board battery. Then switch on the

SPST switch. does the green indicator turn on, and stay on

permanently as long as the power is on?

The circuit will not work, make sure all components

are in the right place.

No

Yes Press either one of the

pressure mats, does the siren sound?

Yes

No

The circuit is not working properly, check for any

faults in the connections.

Press the second pressure mat, does a red Led light up.

Yes No

The red LED indicator on the monstable is not working.

Check if the LED is the right way round.

When both pressure mats have been triggered, does

the siren sound?

Yes

No

There may be a defect in the siren, test it after the circuit has been

thoroughly examined.

Does the siren turn off just when the red LED turns off?

It is most likely the off-board component. Check if the negative and positive

wires are the right way round.

No

Retest the circuit, does it continue to work?

Yes

Yes

Check the circuit, then retest.

START

Finish

Flowchart Test

Description of Process What went well(What did you do to avoid

errors)

Problems encounters or changes made

Action taken to deal with the problem

Design PCB and create mask No problems

Expose Mask and photoPCB to UV No problems

Develop exposed PCB No problems

Etch PCB Tracks were straight and there were no unwanted sections left over from the etching.

Some parts of the tracks had thinner, especially the pads where there was exposed copper.

Extra caution had to be taken when soldering in order to reduce the risk of burning the tracks, which may jeopardise the circuit.

Cut board to size No problems

Drill holes in solder pads Most incisions were made and of the right size. All holes were in the right place; connected to the tracks.

There were some exceptions where the holes were not of the right size. There were also some places where holes were not drilled.

Holes had to be enlarged manually, as well as piercing absent holes, which had to be drilled (manually).

Add resistors All resistors were of the same values, by checking them beforehand, I avoid problems that involved choosing the wrong resistors.

There were problems when getting the variable resistor with the right value. There were no 10K variable resistors.

I substituted the 10k variable resistor with an- other which had the value of 46k.

Add capacitors

I choose the capacitors carefully, looking at its values before putting it onto the circuit.

When soldering, the capacitors were slanted. This was because the capacitor became loose when I rotated the PCB in order to solder the underside.

I ensured that the capacitor was flat on the PCB board. Then I bent the legs on the other side so that the component was temporarily fastened. Afterwards, I soldered the components.

Add Chip socket For most pads, I managed to solder the legs without making any mistakes by soldering carefully.

There were some instances where the molten solder ran onto the adjacent pads.

I use to soldering iron to re-melt the solder, quickly removing the solder while it's still molten.

Add Chip socket Most legs were soldered without complications due to careful soldering.

Sometimes applying too much solder resulted in the solder escaping the pad designed to hold the it.

I used the soldering iron to re-melt it. Then I attempted to remove as much solder as I can using the iron. A solder wick was also used to remove solders left behind.

Shrink wrap connections between off board components and board

All shrink wraps were effective as insulators. So my circuit had no problems with short-circuiting.

Heating the rubber fitting for too long melted an off board component as well. The deformation meant that it no longer worked properly.

I fitted another off board component, this time applying less time shrink wrapping.

Add off board components Select the correct off-board components before fitting them onto the PCB.

No problems

Add chip to socket At first, the chip may be hard to fit. Put enough pressure to push the chip into the socket, however, take care not to bend the legs on the chip.

No problems