PAGE 146 OF 150 · PROJECTS
Build a Traffic Light Model
Three colours step through a timed sequence.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
The sequence
A traffic light model uses red, amber and green LEDs run by a timer or microcontroller.
- UK style: red, then red and amber, then green, then amber, then red.
- US style: red, green, amber, then red.
- A model might use 5 seconds for red and green, and 2 seconds for amber.
Build notes
Use a 330 ohm resistor on each LED at 5 V. Add a pedestrian button that requests a red phase, and a second set of lights to model a junction, making sure the two sets are never green together.
REMEMBER
Never allow conflicting greens in a model junction.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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