How to Control an Arduino from a Raspberry Pi

The “should I use a Raspberry Pi, or should I use an Arduino” question always comes up in the first stages of product development. Honestly, who wouldn’t be confused? Both boards are popular, but there are subtle differences in their optimal use cases.

The Raspberry Pi is a computer, so it uses an operating system. This creates multiple layers of abstraction that make real-time signal generation and detection unreliable. On the other hand, the Arduino can read and write electronic signals much faster and more reliably than the Raspberry Pi.

Luckily the Arduino and Raspberry Pi can be used together to take advantage of features from each board.

In this tutorial we will learn how to control the Arduino’s GPIO pins with a Python program run on the Raspberry Pi. The Arduino will be connected to the Raspberry Pi directly with a USB cable. To do this, we will use a protocol called Firmata.

Firmata

Firmata is a communication protocol that connects a microcontroller to software on a host computer. Think of Firmata as a language that the Raspberry Pi and the Arduino both understand.

Setting Up the Arduino

The easiest way to setup Firmata on the Arduino is by using the Raspberry Pi. First, we need to install the required software.

1. Connect the Raspberry Pi to the internet. Open command terminal and enter the following command:

sudo apt-get -y install arduino python-serial mercurial

2. Now, connect the Arduino to the Raspberry Pi with an A to B USB cable.

3. Open the Arduino IDE, and select the correct port for the device.

4. Next, upload the PyFirmata firmware to the Arduino by opening the sketch from File > Examples >  Firmata > Standard Firmata.

5. Finally, click the upload button.

Setting Up the Raspberry Pi

To prepare the Raspberry Pi:

1. First, install the pyFirmata files by entering this:

git clone https://github.com/tino/pyFirmata

2. Then, run the following commands:

cd pyFirmata
sudo python setup.py install

Preparing the Hardware

To demonstrate how Firmata works, we will build a project that uses a Python program on the Raspberry Pi to control the Arduino’s GPIO pins. We will connect a button and LED to the Arduino so that the LED lights up when the button is pressed.

To build this project, we need the following components:

• Raspberry Pi
• Arduino Uno
• Jumper wires
• Breadboard
• Tactile push button
• One LED
• One 220 Ohm resistor
• A to B USB cable

Follow this diagram to connect the LED and push button to the Arduino. The Arduino is connected to the Raspberry Pi with an A to B USB cable like this:

To learn more about the Arduino, check out our Ultimate Guide to the Arduino video course. We teach Arduino programming and circuit building techniques that will prepare you to build any project.

Python Code

Copy the code below to your Raspberry Pi and save it as a “.py” file. Run the program by typing python filename.py:

import pyfirmata

led_pin = 7
button_pin = 8

board = pyfirmata.Arduino("/dev/ttyACM0")

while True:
    if board.digital[button_pin].read(1):
        board.digital[led_pin].write(1)
    else:
        board.digital[led_pin].write(0)

Code Explanation

First, we import the pyfirmata library using import pyfirmata. Then we label the LED and button pins by storing them into variables: led_pin and button_pin. To make this program connect to the Arduino, we need to tell it the port where the Arduino is connected. Use pyfirmata.Arduino() and then create the instance by assigning the port in the board variable. In this case it’s /dev/ttyACM0.

The while loop basically acts like void setup(). We use an if statement to monitor the status of the button. If the button sends a HIGH signal, meaning it was pressed, the LED lights up. Both use the digital[].read and digital[].write methods to control the GPIO pins on the Arduino.

Now when you press the button the LED should light up. Press CTRL + C to stop the program.

Hope this tutorial has helped you to understand how to control the Arduino with a Raspberry Pi. Leave a comment below if you have any questions!