I made a simple HAT (Hardware Attached on Top) for the Raspberry Pi to read multiple DS18B20 temperature sensors — it was surprisingly easy. I used the measured temperatures to control a fan using Home Assistant.
Table of contents
I started testing with a single DS18B20 break-out board.
First we need to do a couple of things on the Pi:
- Enable 1-wire communication with
- Install python package
sudo apt install python3-w1thermsensor
Now — let’s try to list the connected 1-wire devices:
$ ls /sys/bus/w1/devices/ 28-0416a02b0eff w1_bus_master1
Alright, we have one device! Now to read the temperature:
$ cat /sys/bus/w1/devices/28-0416a02b0eff/w1_slave 8e 01 4b 46 7f ff 0c 10 de : crc=de YES 8e 01 4b 46 7f ff 0c 10 de t=24875
24875 = 24.875°C
Making the HAT
To make something more permanent — I used a 30×70 mm prototyping perfboard, schematic diagram and parts list below.
On the underside I attached a female pin-header for the Raspberry Pi GPIO ports.
And on the top; five 3-pin male pin-headers for DS18B20 temperature sensors, and a 10k pull-up resistor. All the 3-pin male pin-headers are connected in series.
Only three pins are needed to connect to the Raspberry Pi; VDD (5V), GND and GPIO4 (1-wire). I’m using a 20-pin header because it makes the HAT attach more firmly.
I connected a couple more DS18B20 temperature sensors and listed their IDs:
$ ls /sys/bus/w1/devices/ 28-0416a02b0eff 28-0517021db9ff 28-051702869eff w1_bus_master1
Reading the sensors
To read the sensor values I made a tiny python script.
- Source code is available in a git repository:
It reads each sensor every 15 seconds and publishes the measurements over MQTT, it also calculates the average of all the connected sensors and publishes that.
See it in action here:
My Home Assistant subscribes to the temperature measurements over MQTT, and I use the average temperature from all sensors to control the home office exhaust fan.
sensor: - platform: mqtt state_topic: 'sensor/office/temp/above_rack' availability_topic: "sensor/office/temp/above_rack/status" name: 'Office ceiling above rack' unit_of_measurement: '°C' - platform: mqtt state_topic: 'sensor/office/temp/above_desk' availability_topic: "sensor/office/temp/above_desk/status" name: 'Office ceiling above desk' unit_of_measurement: '°C' - platform: mqtt state_topic: 'sensor/office/temp/room_center' availability_topic: "sensor/office/temp/room_center/status" name: 'Office ceiling center' unit_of_measurement: '°C' - platform: mqtt state_topic: 'sensor/office/temp/average' name: office_temp_average unit_of_measurement: '°C'
- alias: Fan on auto trigger: platform: numeric_state entity_id: sensor.office_temp_average above: 25 action: service: switch.turn_on entity_id: switch.office_fan - alias: Fan off auto trigger: platform: numeric_state entity_id: sensor.office_temp_average below: 24 for: minutes: 5 action: service: switch.turn_off entity_id: switch.office_fan
- 1 × microSDHC card, Transcend, 32GB, class 10, 20MB/17MBs
- 1 × PCB, perfboard prototyping, 30x70mm, 21cm2
- 1 × Raspberry Pi 1 Model B+, 700MHz ARM CPU, 512MB RAM
- 1 × Resistor, carbon film, 0.25W, 10 kΩ, 5%
- 1 × Rubber foot, adhesive, SJ-5012, Ø 12.7x3.5 mm
- 10 × Straight pin header, female, Dual row, 2.54mm
- 12 × Straight pin header, female, Single row, 2.54mm
- 15 × Straight pin header, male, Single row, 2.54mm
- 4 × Temperature sensor DS18B20, probe, Water-proof, 1M cable
- 1.5 m Wire, stranded, 0.22mm2, Black
- 1.5 m Wire, stranded, 0.22mm2, Red
- 1.5 m Wire, stranded, 0.22mm2, Yellow
Last commit 2023-01-15, with message: Add MQTT tag, use shortcode for git repository