The first step with any new hardware is the 'hello world' of electronics - blinking an LED. This is very easy with CircuitPython and Coral. We'll extend the example to also show how to wire up a button/switch.
Note that the GPIO pins on the Coral roughly correspond to the Raspberry Pi GPIO
Similarities:
- 5V, 3.3V and GND pins are all in the same locations
- Main I2C port is on pins #3 and #5
- Main SPI port is on pins #19, 21, 23, 24 and 26
- Main UART port is on pins #8 and #10 note that this is shared with the console so you will conflict with the built in serial console unless you disable the console on these pins
- I2S is available on same pins as Raspberry Pi
Differences:
- There's a UART3 on pins #7 and #11 but these don't seem to be available (
/dev/ttymxc2does not exist) so these pins cannot be used for GPIO - I2S is enabled by default so you cannot use pins #12, 35, 38, 40 for GPIO
- PWM is enabled on pins #15, #32 and #33 so these pins cannot be used for GPIO but you can use them to create PWM outputs
- The secondary I2C port is available for you to use (pins #27 and #28)
- Raspberry Pi GPIO #22 is known as GPIO_P13
- Raspberry Pi GPIO #23 is known as GPIO_P16 (output only)
- Raspberry Pi GPIO #24 is known as GPIO_P18
- Raspberry Pi GPIO #25 is known as GPIO_P22
- Raspberry Pi GPIO #5 is known as GPIO_P29
- Raspberry Pi GPIO #6 is known as GPIO_P31
- Raspberry Pi GPIO #16 is known as GPIO_P36
- Raspberry Pi GPIO #26 is known as GPIO_P37 (output only)
Any old LED will work just fine as long as its not an IR LED (you can't see those) and a 470 to 2.2K resistor
Some tactile buttons or switches
We recommend using a breadboard and some female-male wires.
You can use a Cobbler to make this a little easier, the pins will be labeled according to Raspberry Pi names so just check the Coral names!
Wiring
Connect the Coral Ground pin to the blue ground rail on the breadboard.
- Connect one side of the tactile switch to Coral GPIO_P13
- Connect a ~10K pull up resistor from GPIO_P13 to 3.3V
- Connect the other side of the tactile switch to the ground rail
- Connect the longer/positive pin of the LED to Coral GPIO_P16
- Connect the shorter/negative pin of the LED to a 470ohm to 2.2K resistor, the other side of the resistor goes to ground rail
There's no Coral Fritzing object, so we sub'd a Raspberry Pi in
Double-check you have the right wires connected to the right location, it can be tough to keep track of pins as there are forty of them!
No additional libraries are needed so we can go straight on to the example code
However, we recommend running a pip3 update!
pip3 install --upgrade adafruit_blinka
Blinky Time!
The finish line is right up ahead, lets start with an example that blinks the LED on and off once a second (half a second on, half a second off):
import time
import board
import digitalio
print("hello blinky!")
led = digitalio.DigitalInOut(board.GPIO_P16)
led.direction = digitalio.Direction.OUTPUT
while True:
led.value = True
time.sleep(0.5)
led.value = False
time.sleep(0.5)
Verify the LED is blinking. If not, check that it's wired to GPIO #16, the resistor is installed correctly, and you have a Ground wire to the Coral.
Type Control-C to quit
Button It Up
Now that you have the LED working, lets add code so the LED turns on whenever the button is pressed
import time
import board
import digitalio
print("press the button!")
led = digitalio.DigitalInOut(board.GPIO_P16)
led.direction = digitalio.Direction.OUTPUT
button = digitalio.DigitalInOut(board.GPIO_P13)
button.direction = digitalio.Direction.INPUT
# use an external pullup since we don't have internal PU's
#button.pull = digitalio.Pull.UP
while True:
led.value = not button.value # light when button is pressed!
Press the button - see that the LED lights up!
Type Control-C to quit
