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Lighting an LED

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Lighting an LED

LEDs are delicate devices. If you put too much current through them they will pop (sometimes quite spectacularly). To limit the current going through the LED, you should always use a resistor in series with it.

Try connecting the long leg of an LED to the Pi's 3V3 and the short leg to a GND pin. The resistor can be anything over about 50Ω.

The LED should light up. It will always be on, because it's connected to a 3V3 pin, which is itself always on.


Now try moving it from 3V3 to GPIO pin 17:

The LED should now turn off, but now it's on a GPIO pin, and can therefore be controlled by code.


Switching an LED on and off

GPIO Zero is a new Python library which provides a simple interface to everyday GPIO components. It comes installed by default in Raspbian.

  • Open Mu.

  • You can switch an LED on and off by typing commands directly into the REPL. Click on the REPL button in the menu bar.

  • First import the GPIO Zero library, and tell the Pi which GPIO pin you are using - in this case pin 17.

    In [1]: from gpiozero import LED
    In [2]: led = LED(17)
    

    Press Enter on the keyboard.

  • To make the LED switch on, type the following and press Enter:

    In [3]: led.on()
    
  • To make it switch off you can type:

    In [4]: led.off()
    
  • Your LED should switch on and then off again. But that's not all you can do.