Ds18b20/ nodemcu fluctuations in temp



  • I have two DS18B20 connected to an nodemcu on pin d6. They have a pull up resistor across data and VIC of 4k7. Nodemcu is running tasmota. I am able to see both sensor temps but temp-1 has continuous temp errors. It will show the current temp then shows 85c, then back to the correct temp. This shows on the tasmota main menu as well as through mqtt and node red. I created a 5 and 12 hour chart which showed temp-1 fluctuating constantly.

    Please help



  • @mjdula
    This is not a support forum for Tasmota. You should try their Discord


  • Hero Member

    @mjdula
    The 85 reading is actually an error message used by the ds18b20 to indicate it has not had time to complete the processing of the reading. Most commonly this is only seen when the node first boots up and can be ignored or fixed by adding a small delay. You will find a lot of information on this if you do a google search. I have never experienced it myself but from other posts on the net it seems power supply problems and long cable runs to the sensor can also cause the error. Some have also had success by using a different resistor value. Note you only need one resistor fitted near your nodemcu not a resistor at each ds18b20.
    If the 85 reading is well outside your expected reading you could just filter out any readings over 84 as well.



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