Adding external temperature sensors

The Gateway has an additional connector for connecting external temperature sensors.

Supported sensors

Sensors supported are of the Dallas types:

  • DS1822
  • DS18S20
  • DS18B20
  • DS1825

Multiple sensors can be connected to the connector at the same time and they can be run in normal or parasitic mode.

Connecting sensors

On the right side of the board below the Wemos you can find a 3-pin 2.5mm pitch JST XH connector. If you purchased a complete kit a JST cable is included. If you need to source this cable yourself then look for RC car battery cables. These are usually the same ones.

JST connector

The oldest Gateways have a different pinout. Gateways delivered after July 2019 are all version >V1.0.

Gateways < V1.0: When seen from the front the left pin is GND, the middle pin goes to D5 of the Wemos and the right pin is 3V3. Gateways > V1.0: When seen from the front the left pin is D5, the middle pin goes to GND of the Wemos and the right pin is 3V3. A 4k7 pull up resistor is already on the board. For Gateways < V1.0: If you use the supplied JST cable, please be advised the 3 wires do not color match general waterproof DS18B20 sensor wires!

Sensor pull up resistor

For most cases the pull-up on the board is sufficient. However, if you connect too many sensors or the wires are very long, the pull-up resistor value will be to high. You need to add a through hole resistor on position R20 (also below the Wemos). This optional through hole resistor is routed in parallel to the 4k7 resistor. Recommended in that case is to use a 4k7 resistor, so the final resistor value will be 2k3. If you don’t have the equipment or skills to solder the resistor, you can also insert the resistor in a screw connector like below. You can solder one or more DS18B20 sensors to the JST cable or use f.i. a screw terminal. Please be advised (waterproof) DS18B20 sensors from AliExpress etc are often fake and will have an offset of sometimes 2 degrees Celcius.

Gateway configuration

After adding the sensors, reboot the Gateway and go to the System Status page of the web interface. Scroll down to the MQTT log and see if there is a message of the type ‘sensors’.

Sensors MQTT string

If you can’t see this message, then the Gateway has not detected the sensors. Check the wiring. If wired correctly, you should see an entry for each sensor.

To find out which sensor is which, hold it in your hand or heat it up otherwise individually to see which of the sensors in the log has heated up.