Reading 1-Wire Sensor Data with the Omega

Tutorial written by Onion Community member Omega303

This tutorial is on how to set up the 1-Wire interface, connect sensors to GPIO pins and read sensor data with the Omega.

The Omega can read sensor data via 1-Wire bus system connected to GPIO pins.

Connecting Hardware

1-Wire sensors provide 3 connectors:

• Power Supply (3.3 V)
• GND (ground)
• DQ (data line)

Read your sensors data sheet to identify the appropriate pins!

Connect the sensors:

• Where # can be any of the available GPIO pins [0, 1, 6, 7, 8, 12 ,13, 14, 18, 19, 23, 26]
• For the sake of this tutorial use GPIO 19
• The dimension of the pullup resistor may defer depending on:
  • the actual sensor (some may have built-in resistors)
  • the number of sensors connected
  • the length of the connection wire

Setting up 1-Wire Bus System

Steps to setup 1-Wire bus system:

1. Ensure you are on Omega firmware b270 or higher
2. Configure the GPIO pin connected to the data line of the sensor
   • echo "w1-gpio-custom bus0=0,19,0" > /etc/modules.d/55-w1-gpio-custom
     • replace 19 with the GPIO pin # you want to use
3. reboot your Omega
   • Check if the following folder exists:
     • /sys/devices/w1_bus_master1/28-000123456789/
     • Where 28-000123456789 is a unique id of your sensor and may look similar but not equally

Read the Sensor Data

1. Read raw sensor data
   • cat /sys/devices/w1_bus_master1/28-000123456789/w1_slave
   • prints something similar for a temperature sensor [DS18B20]

     63 01 4b 46 7f ff 0c 10 d1 : crc=d1 YES
     63 01 4b 46 7f ff 0c 10 d1 t=22187
     

2. Trimmed and formatted (for DS18B20)
   • awk -F= '/t=/ {printf "%.03f\n", $2/1000}' /sys/devices/w1_bus_master1/28-000123456789/w1_slave
   • would return

     22.187