# Reading the Raspberry Pi serial port

Many related devices and sensors publish their data directly to a serial port. This includes connected Arduinos.

This tutorial shows you how to read from a serial port while inside a Docker container. It assumes you're either familiar with Docker, or have followed the dockerized script tutorial.

# Source code

On your Pi, create a new directory serialscript. In it, create two files:

script.py

"""
Example for reading from a serial port inside a container

Dependencies:
- pyserial
"""

import serial

# This is the default serial port
PORT = '/dev/ttyACM0'

# You may need to further configure settings
# See the pyserial documentation for more info
# https://pythonhosted.org/pyserial/pyserial_api.html#classes
ser = serial.Serial(port=PORT,
                    baudrate=9600,
                    timeout=1)

try:
    while True:
        # Read raw data from the stream
        # Convert the binary string to a normal string
        # Remove the trailing newline character
        message = ser.readline().decode().rstrip()

        print(f'recv {message}')
finally:
    ser.close()

Dockerfile

FROM python:3.7-slim

COPY script.py /app/script.py

RUN pip3 install pyserial

CMD ["python3", "-u", "/app/script.py"]

# Building

Your serialscript directory should look like this:

.
├── script.py
└── Dockerfile

To build the image, run:

docker build --tag serialscript serialscript/

# Running

To access the serial port on the host computer, your Docker container needs elevated privileges.

Start the container by running:

docker run --rm --privileged --tty --volume /dev:/dev serialscript
  • --rm removes the container after it stops. This prevents leftovers.
  • --tty (or -t) assigns a tty to the container, to immediately see print() output.
  • --privileged gives the container the required permissions to use the serial port.
  • --volume /dev:/dev lets the container 'see' the serial port.
  • serialscript is the name of the Docker image.

WARNING

--volume /dev:/dev also lets the container see all files on the host. Be careful when using this, and avoid exposing ports on this container.