This page describes an experiment in using PyMata Express to communicate (using Firmata) between a Raspberry Pi and an Arduino microcontroller using a serial connection. To see how to intercommunicate over I2C, see Raspberry Pi to Arduino over I2C.
To install Pymata Express on Linux (including Raspberry Pi) and macOS computers, open a terminal window and type:
sudo pip3 install pymata-express
The FirmataExpress page describes how to install it on an Arduino, using the Arduino IDE.
In a nutshell, this is not too difficult:
Then your Raspberry Pi can communicate with it using Python scripts, an example of which is shown below.
Here is an example demonstrating using a callback to monitor the state changes of a digital input pin.
import asyncio import time import sys from pymata_express import pymata_express """ Setup a pin for digital input and monitor its changes using a callback. """ # Setup a pin for analog input and monitor its changes DIGITAL_PIN = 12 # arduino pin number IDLE_TIME = .001 # number of seconds for idle loop to sleep # Callback data indices # Callback data indices CB_PIN_MODE = 0 CB_PIN = 1 CB_VALUE = 2 CB_TIME = 3 async def the_callback(data): """ A callback function to report data changes. This will print the pin number, its reported value and the date and time when the change occurred :param data: [[pin, current reported value, pin_mode, timestamp] """ date = time.strftime('%Y-%m-%d %H:%M:%S', time.localtime(data[[CB_TIME])) print(f'Pin: {data[[CB_PIN]} Value: {data[[CB_VALUE]} Time Stamp: {date}') async def digital_in(my_board, pin): """ This function establishes the pin as a digital input. Any changes on this pin will be reported through the call back function. :param my_board: a pymata_express instance :param pin: Arduino pin number """ # set the pin mode await my_board.set_pin_mode_digital_input(pin, callback=the_callback) while True: try: await asyncio.sleep(IDLE_TIME) except KeyboardInterrupt: await board.shutdown() sys.exit(0) # get the event loop loop = asyncio.get_event_loop() # instantiate pymata_express board = pymata_express.PymataExpress() try: # start the main function loop.run_until_complete(digital_in(board, 12)) except (KeyboardInterrupt, RuntimeError) as e: loop.run_until_complete(board.shutdown()) sys.exit(0)