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LED

The led folder contains 3 Python scripts that:

  • control a LED via some commands
  • simulate a traffic light via 3 LEDs
  • web client for controllig the 3 LEDs

Male-female jumper wires may be needed.

How to manually control a LED?

Suppose the following wiring is made: 

GPIO18 (12) -> Breadboard (+) -> Resistor (220 Ω) -> LED long leg (+, anode)
GND    (14) -> Breadboard (-) -> LED short leg (-, cathode)

When the pin is HIGH (dh), the LED lights. When it is LOW (dl), the LED turns off.

Turn on the LED: 

pinctrl set <GPIO> op dh

and to turn off: 

pinctrl set <GPIO> op dl

To get the state of the GPIO pin, run: 

pinctrl get <GPIO>

To reset the GPIO pin state, run: 

pinctrl set <GPIO> no

Tips

  • Use pinout command to check the schema of the GPIO pins. Or visit pinout.xyz.
  • Do not connect an LED directly to a GPIO pin without a resistor. The resistor limits current. Think of it as a small speed limit for electricity.
  • The long LED leg is usually the positive side, called anode. The short LED leg is usually the negative side, called cathode, and goes to GND.