DS18b20 with RPi - connections

Domoticz part 4: connecting the DS18b20 thermometer

Temperature readout is one of the first sensor we add to domoticz. It’s a very simple task and allows to connect multiple thermometers via the 1-wire bus. 1-wire means that thermometer has a single data wire, on top of VCC and GND. This wire is used to send back data to 1-wire controller and then it gets verified.

Termometr DS18b20
Thermometr DS18b20

What will you need?

Hardware:

  • thermometer DS18B20 (Dallas) – comes in variety of housings – usually it’s a chip with 3 pins. It’s good to measure from -55 degrees Celsius and up to +125, but it’s accurate till about +95 – +100.
  • 4,7kOhm resistor – used to pull up to VCC the data pin
  • Raspberry Pi (any model – A, B, B+, 2, 3 or new Zero)

Software:

  • domoticz – the same we installed in part one

Let’s do it!

This thermometer is able to perform very well on a long cable, being powered just by RPi using the PIN +3,3V. It’s OK to get 20 meters of calbe with 5 such thermometers, to check on recuperator and chimney. Recuperator has 2 inputs and two outputs – this allows to use the ‘custom’ mode of drawing the temp graphs to check on it’s performance.
Now first thing is to change the way our Wheezy or Jessie Raspbian starts. Add to /boot/config.txt this line:

Now reboot RPi and connect the thermometer – add the 4,7kOhm resistor between the (red) data pin and the +3,3V (white) – just like on the first picture. This will make the signal crisp & clear on the 1-wire bus. The GND is using (blue) cable. All set? Connect to Raspberry Pi in this way:

Connecting Dallas DS18b20 to Raspberry Pi
Connecting Dallas DS18b20 to Raspberry Pi

Pin +3,3V to +3,3V, Pin Data (the middle on the thermometer) to GPIO#4 on RPi, and GND to GND of RPi (blue). If you have more (i.e. 5) connect them in parallel.
Now – let’s use console to find out if RPi can see the thermometer on the 1-wire bus:

Now you should get RAW readout of the temperature – this example shows the real system with 5 thermometers:

You should expect just one entry for single thermometer. The part crc=xx YES – tells you that we have good readout.
All that’s left is to add the 1-wire to domoticz, using: Settings->Hardware:

Adding 1-wire to Domoticz
Adding 1-wire to Domoticz

Our themometer(s) will be at once visible via Settings->Devices:

Dallas tehrmometers DS18b20 in Domoticz (1-wire)
Dallas tehrmometers DS18b20 in Domoticz (1-wire)

This is really all – add them to make’em visible in Temperature tab!