safety lights
TRANSCRIPT
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Design Brief
Design and make a pedestrian / cyclist safety light.
The safety light must be programmed to flash highbrightness LEDs on and off.
Research homework:Complete research to enable you to decide what type of
product you will design. Areas of investigation shouldinclude:
Research of pedestrian/cycle safety products already onthe market that utilise LEDs or that could be developedto utilise LEDs
Research of the situation why would
cyclists/pedestrians need a safety light?
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The E.R. Thomas Motor Company's
"Auto-Bi" or "Auto-Bike" began
production in 1901, making E.R.
Thomas one of the first manufacturers
in the United States to mass-producemotor driven cycles.
Auto-Bi Kerosene
Headlamp
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Design Specification
Points to include:
The design will use a PICAXE-08
microcontroller as its controller.
The design will include 3 high brightness LEDs.
The design will be able to optionally react to
changes in light levels.Add further points that are of importance to
your target market and research
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Printed Circuit Board
Track SideThis side contains the circuit
(tracks) that joint the
components together
Component SideThis side is where the components
are (usually) mounted
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Fixed resistor
This fixed resistor has a fixed
resistance which is indicated
by a colour code.
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2
3
? ?
1
330 (ohms) 4700 (4.7k)
47000 (47k)
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Light Emitting DiodesThese can be red, green,
amber or yellow in colour.They must be connected
the right way round.
The positive leg of an LED is longer
than the negative leg.
The negative leg also has a flat edgeon the plastic casing of the LED.
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A battery (cell) is a self-contained source of electrical energy.
It is a portable power supply.
Batteries contain chemicals that store energy.
When connected into a circuit this chemical energy is converted
to electrical energy that can then power the circuit.
Batteries and Battery Box
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Slider Switch
Used to switch the circuit On or Off
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Microcontrollers are purchased blank and
then programmed with a specific
control program. Once programmed the
microcontroller is built into a
product to make the product more intelligent
and easier to use.
Microcontrollers are used as the brain in
electronic circuits.
Microcontrollers are used in automatically
controlled products and devices, such as
automobile engine control systems, remote
controls, office machines, appliances, power
tools, and toys.
Microcontroller
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IC Socket
IC sockets provide an advantage over directly
attaching microcontrollers to the PCB by
making it easier to replace the processor in the
event of a failure. The microcontroller is often
the most expensive component in the system
and the cost of a IC socket is relatively low.
The IC sockets is soldered to the PCB and
The microcontroller is plugged into it.
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Download Socket
The download socket is used to connect
the PCB to a computer.
The programme created on the
computer can then be downloaded to
the microcontroller
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A Light Dependent Resistor (LDR) is special
type of resistor that reacts to changes in light
level. The resistance of the LDR changes as
different amounts of light fall on the top
'window' of the device. This allows electroniccircuits to measure changes in light level.
Light Dependant Resistor - LDR
LDRs are used in automatic street lamps to
switch them on at night and off during the
day. They are also used within many alarm and
toys to measure light levels.
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Safety Light Components
PCB printed circuit board
R1, R2, R3 120R resistor (brown red brown gold)
R4 10k resistor (brown black orange gold)
R5 22k resistor (red red orange gold)
R6 10k resistor (brown black orange gold)
LED1, 2, 3 High brightness LEDs SW1 On/off slide switch
IC1 8 pin IC socket
IC1 PICAXE-08 microcontroller
CT1 PICAXE download 3.5mm socket
BT1 3V (2xAAA) battery wire To connect LEDs
LDR Miniature light dependent resistor
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Component positions are printed on PCB
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Place the three 120 (brown red brown gold) resistors in positions R1, R2 and R3
R1
R2
R3
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Place the two 10k (brown black orange gold) resistor in positions R4 & R6.
R4
R6
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Place the 22k (red red orange gold) resistor in position R5
R5
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Push the download socket onto the PCB and make sure it clicks into
position (so that it lies flat on the board).
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Push the IC socket into position.
Make sure the notch at one end points towards the resistors.
Notch
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Solder the slide switch in position.
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Place the first LED into position marked LED1
Make sure the legs are in the correct positions.
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Make sure the bottom of the LED is level with the top of
the switch i.e. the LED is about 6mm above the PCB.
6 mm
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Bend the LED around the edge of the PCB so the LED
is now on the track side of the PCB
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Connect the wires from the battery case in the position marked BT
Note: Black = negative & Red = positive
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Cut 4 wires (2 red, 2 black) 100mm long.
Solder one red (+ve) and one black (-ve) wire to LED2 & LED3
Slide on insulating tubing.
Long leg +ve
Short leg -ve
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Solder the other ends of the wires from the LEDs to the PCB
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Remember red +ve & black -ve
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Solder the Light Dependant Resistor LDR on the TRACK side of the board.
It should be left raised on legs approximately 5mm above the board.
5mm
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Location of LDR viewed from component side.
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Insert the microcontroller into the socket,
ensuring the notch faces the resistors.
Notch
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Programming the Safety Light
To create a programme to control how the safety light will operate we will be using
computer program called PICAXE
To create the program we will be using a programming language called BASIC
This program will then be downloaded to the microcontroller (the brain) on our
safety light
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BASIC Language (1)
The three LEDs in the safety light are numbered LED1=0 LED2=1 & LED3=2
All BASIC programs should start with a label.
A label is a name followed by a colon (:) for example;
main: or start:
English Language
switch on LED number1
switch off LED number1
wait for 1 second before going to next command
go back to the beginning of the program
BASIC Language
high 0
low 0
wait 1
goto main
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Program to check LEDs
main:
high 0
wait 1low 0
wait 1
goto main
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BASIC Language (2)
The LDR (light dependant resistor) in our circuit is called pin3It has a value of1 or0
1 - if light is falling on it
0 - if there is no light
Therefore the BASIC command pin3 = 1 means light is falling on LDRand pin3 = 0 means no light is falling on LDR
LOGIC commands, such as if then. commands can be used in BASIC
We can say; if(something is true) then (do something)LOGIC commands make the brain of our circuit more intelligent
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Program to check LDR
main:
if pin3 = 1 then goto LEDon
low 0goto main
LEDon:
high 0
goto main
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BASIC Language (3)
The wait command, used earlier, uses whole second units.
wait 1 means wait for 1 second
wait 2 means wait for 2 seconds etc.
If you want your program to wait for a fraction of a secondthen you must use the pause command.
The pause command uses 1 millisecond units (1000 ms = 1 second)
Examples
pause 1000 means wait 1 secondpause 500 means wait 0.5 seconds
pause 100 means wait 0.1 second
pause 1500 means wait 1.5 seconds
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Program to sense Light or DarkThis program has a main loop which flashes the LEDs on and off fairly slowly.
If the LDR light sensor is in the dark the LEDs will flash on and off much more quickly.slow:
high 0
high 1
high 2
pause 500
if pin3 = 0 then goto fast
low 0
low 1low 2
pause 500
if pin3 = 0 then goto fast
goto slow
fast:
high 0
high 1
high 2
pause 100if pin3 = 1 then slow
low 0
low 1
low 2
pause 100
if pin3 = 1 then slow
goto fast
Label for slow flashes
switch on LED 1
switch on LED 2
switch on LED 3
wait for 0.5 seconds
if it is darkgo to fast flashes label
switch off LED 1
switch off LED 2
switch off LED 3
wait for 0.5 seconds
if it is darkgo to fast flashes label
go to slow flashes label
Label for fast flashes
switch on LED 1
switch on LED 2
switch on LED 3
wait for 0.1 secondsif it is lightgo to slow flashes label
switch off LED 1
switch off LED 2
switch off LED 3
wait for 0.1 seconds
if it is lightgo to slow flashes label
go to fast flashes label
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Advanced BASIC Language (4)
Sometimes it is useful to switch more than one LED on or off at the same time.
This saves time when lots of high and low commands would have to be used together.
The command that does this is called let pins =
After the equals sign a number is used. Each LED is given a value, and the number
used in the program is the sum of these values.
LED3 LED2 LED1
Number(high/low) 2 1 0
Value 4 2 1
Switch on all LEDs
Switch on LED1 & LED2Switch on LED2 & LED3
Switch off all LEDs
let pins = 7
let pins = 3let pins = 6
let pins = 0
Note: Before the let pins = command can be used all LEDs must be switched off
So your programme MUST start with low 0, low 1 and low 2
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BASIC for. next loops
If we want to switch on a LED a specific number of times
we can use a for next loop.The for next.. loop uses a counter or variable.
The PICAXE software can use 14 variables from b1 to b13
Example switch on LED1 15 times then stop.
main:
for b1 = 1 to 15
high 0
pause 500
low 0
pause 500
next b1
end:
Advanced program
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Advanced programThis program uses a number of
for...next loop to create
a number of different patterns.
start:
low 0
low 1
low 2
main:
for b1 = 1 to 20
let pins = 7pause 100
let pins = 0
pause 100
next b1
for b1 = 1 to 20
let pins = 0
pause 200let pins = 1
pause 200let pins = 3
pause 200
let pins = 7
pause 500
next b1
for b1 = 1 to 20
let pins = 1
pause 100
let pins = 0pause 100
let pins = 2
pause 100
let pins =0
pause 100let pins = 4
pause 100
let pins = 0
pause 100