03 30 minutes
Traffic lights
Three LEDs, three pins, one shared ground, and a function that keeps order
Mission goal: Drive red, yellow and green LEDs from GP16, GP17 and GP18, each with its own resistor, and run a believable traffic light sequence using a helper function.
Section 1
Understand
New ideas
- Several circuits sharing one ground
- Writing a function to avoid repeating yourself
- Turning everything off before turning one thing on
- Why each LED needs its own resistor
- 1Three LEDs, three pins, each with its own resistor.
- 2All grounds meet at one shared ground (pin 38).
- 3One function turns everything off, then lights only the chosen colour.
Safety first
- Unplug the USB cable while you add the two extra LEDs.
- Count the physical pins twice. GP18 is physical 24, and physical 23 next to it is ground.
- Three LEDs means three chances to fit an LED backwards. Check all three long legs before powering up.