This page describes experiments in communicating between a Raspberry Pi (as a master) and an Arduino (as a slave) over I²C. The Raspberry Pi is programmed in Python, the Arduino using a sketch (the Arduino's own language).

I based this experiment on an article found on The Robotics Back-End (see References below), but have modified it to use Python rather than C on the Raspberry Pi, since that's the main language I've been using to write the operating system of the KR01 robot. Some of the ideas I found online tended to lock up the I²C bus or cause other kinds of problems. When I stumbled onto an example using the WiringPi library things seemed to even out.

WiringPi is a C++ library for communicating with a Raspberry Pi. It's been ported to Python as the WiringPi-Python library. In particular, I tried using the wiringPiI2CRead() and wiringPiI2CWrite() methods. For documentation, see The I²C Reference Library.

It should be noted that the I²C read and write methods send a single integer. In order to communicate strings or other data, you'll need to serialise the data and then deserialise it on the other end.

For an example, see: How do I serialize a Python dictionary into a string, and then back to a dictionary?

In the end I developed a solution called pimaster2ardslave that has been posted as a project on github, which includes a Raspberry Pi Python 3 script and an Arduino sketch.

I found to my consternation that the Arduino Nano BLE Sense that I bought for the purpose of being used as the slave processor can't be used as a slave: the Wire library it uses hasn't implemented the I²C slave protocol, though this is not documented anywhere (I found this out on the Arduino forum). One of the benefits of the Nano BLE Sense was that it's a 3.3V device, whereas the regular Nano is 5V. I'm still searching for the right Arduino board now... (😠) maybe I'll use a Teensy or an Adafruit board.

Raspberry Pi Installation#

WiringPi for Python can be installed via: 

 sudo pip3 install wiringpi

Arduino Installation#

You'll need to install an Arduino sketch on your Arduino using the Arduino IDE. As an example, I modified the original source to blink the Arduino's built-in LEDs when either a transmit (TX) or receive (RX) event occurs. 

#include <Wire.h>
#define SLAVE_ADDRESS 0x08
byte data_to_echo = 0;

// this slave code is meant to work on I2C address 0x08
// with rpi_arduino_wiringpi_i2c.cpp as described at:
// https://roboticsbackend.com/raspberry-pi-master-arduino-slave-i2c-communication-with-wiringpi/

void setup()
{
  Wire.begin(SLAVE_ADDRESS);
  Wire.onReceive(receiveData);
  Wire.onRequest(sendData);
  ready_blink();
}

void loop() {

}

void receiveData(int bytecount)
{
  for (int i = 0; i < bytecount; i++) {
    data_to_echo = Wire.read();
  }
  blink_rx();
}

void sendData()
{
  Wire.write(data_to_echo);
  blink_tx();
}

// status displays .....................................................

void ready_blink() {
  int i = 0;
  while ( i < 800 ) {
    blink_builtin();
    delay(i);
    i = i + 50;
  }
}

void blink_builtin() {
  digitalWrite(LED_BUILTIN, HIGH);      // turn the LED on (HIGH is the voltage level)
  delay(100);                           // wait 100ms
  digitalWrite(LED_BUILTIN, LOW);       // turn the LED off by making the voltage LOW
}

void blink_tx() {
  digitalWrite(LED_BUILTIN_TX, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(100);                           // wait 100ms
  digitalWrite(LED_BUILTIN_TX, LOW);    // turn the LED off by making the voltage LOW
}

void blink_rx() {
  digitalWrite(LED_BUILTIN_RX, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(100);                           // wait 100ms
  digitalWrite(LED_BUILTIN_RX, LOW);    // turn the LED off by making the voltage LOW
}

References#

Arduino#

Tags:  Raspberry Pi, Arduino

This page (revision-10) was last changed on 2021-06-19 07:56 by Murray AltheimTop