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General-Purpose Input/Output (GPIO)

In the Getting Started with GreatFET tutorial, we blinked one of the built-in LEDs. Now let's learn how to manipulate General-Purpose Input/Output (GPIO) pins so that we can interface with external LEDs or other devices!

You'll need a few things to follow this tutorial:

  • GreatFET One (also known as Azalea)
  • Solderless Breadboard Neighbor for GreatFET (also known as Daffodil) or any breadboard
  • a through-hole LED
  • a current-limiting resistor (any value from 200 ohms to 2000 ohms should be fine)

Controlling an external LED

Connect the LED

Plug the shorter lead of the LED into pin 1 on header J1 and the longer lead of the LED into a breadboard. Plug one lead of the resistor into the same row of the breadboard, and plug its other lead into pin 4 on header J1.

FIXME photo

Open an interactive Python shell:

gf shell

Select a pin by number:

pin = gf.gpio.get_pin('J1_P4')

Configure the pin as an output:

pin.set_direction(gf.gpio.DIRECTION_OUT)

Turn on the LED:

pin.write(True)

Turn off the LED:

pin.write(False)

Blink the LED:

import time
for i in range(10):
	pin.write(not pin.read())
	time.sleep(0.2)

GPIO input

Configure the pin as an input:

pin.set_direction(gf.gpio.DIRECTION_IN)

Disconnect the LED and use the resistor to connect pin 4 to pin 1 on header J1. This connects the input to GND (0 V).

pin.read()

The read() method should return False, indicating that a low voltage is connected to the input.

Now disconnect the resistor from pin 1 and connect it to VCC (3.3 V) on pin 2. It should now connect pin 2 to pin 4 on header J1.

pin.read()

The read() method should return True, indicating that a high voltage is connected to the input.