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.
WiringPi (both C++ and Python versions) has an I2C class to provide communication over I2C. The basic API is as follows:
class I2C(object):
def setupInterface(self,*args):
return wiringPiI2CSetupInterface(*args)
def setup(self,*args):
return wiringPiI2CSetup(*args)
def read(self,*args):
return wiringPiI2CRead(*args)
def readReg8(self,*args):
return wiringPiI2CReadReg8(*args)
def readReg16(self,*args):
return wiringPiI2CReadReg16(*args)
def write(self,*args):
return wiringPiI2CWrite(*args)
def writeReg8(self,*args):
return wiringPiI2CWriteReg8(*args)
def writeReg16(self,*args):
return wiringPiI2CWriteReg16(*args)
In particular, we can expect to be 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?
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#
- WiringPi (C++ library)
- WiringPi-Python on github
- Raspberry Pi (master) Arduino (slave) I2C communication with WiringPi
- From Raspi.TV an article on WiringPi2 (really only the first is relevant here):
- i2c SLAVE on Adafruit's CircuitPython forum
- Raspberry Pi - Arduino Serial Communication