Traffic Signal
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This example uses three LEDs to make a model traffic light signal. You can use all red LEDs if you like, but its more realistic if you use red, yellow and green.
The LEDs cycle around in the sequence red, green, yellow and then back to red again
Please ensure that you have mBlock setup on you computer. Click to setup mBlock
You will need the following parts:
1x arduino uno
1x arduino uno USB Cable
1x Breadboard
4x Jumper Wire
1x Red LED
1x Yellow LED
1x Green LED
3x Resistors
You purchased your Arduino kit from
To add the extra LEDs and resistors, wire them up as shown in the breadboard layout below.
Ensure that the LEDs are the right way around, with the longer positive leads (anodes) to the left.
Think of how a traffic light works.
it starts from RED
then turns to GREEN
then turns YELLOW
and back to RED
Think about the how long the light stays on before it changes to the next colour
This time that it takes before the light changes is called a WAIT in coding. So the program will WAIT for a specific number of seconds before the next light changes to the next colour
In order to turn the light ON or OFF in code, we say that if we want the light on then we need to set it to HIGH and if we want the light OFF we setup it to LOW.
So to change the traffic lights we say
to make the light ON, we set it to HIGH
to make the light OFF, we set it to LOW
If you look at the wiring diagram above, you will see that we connected it as follows
we connected DIGITAL PIN 7 (D7) to the RED light
we connect DIGITAL PIN 6 (D6) to the YELLOW light
we connect DIGITAL PIN 5 (D5) to the GREEN light
So In order for the program to work we will do the following
set D7 to HIGH (red light)
set D6 to LOW (yellow light)
set D5 to LOW (green light)
WAIT for 10 seconds
set D7 to LOW (red light)
set D6 to LOW (yellow light)
set D5 to HIGH (green light)
WAIT for 10 seconds
set D7 to LOW (red light)
set D6 to HIGH (yellow light)
set D5 to LOW (green light)
WAIT for 1 seconds
