I am using 2 DS18B20 temperature sensors connected to my raspi. They are connected to a 5 meter long cable together with a DHT11 humidity sensor, do they share plus and minus. The problem I have is both the sensors are returning really high values above 80°C. I heard they return 85°C when they fail, but that seems not to be the case here as they return like 83.6 for example. Is anyone experiencing similar problems?

Also the DHT11 sensors reports >90% humidity, could that be the problem?

EDIT: the cable I have has 4 wires. 2 are used for power and get shared between the 3 sensors. The 2 wires left are for the dht11 and the 1-wire interface. Also this does not happen all the time. Most of the time it worls great. I have another ds18b20 near the raspberry inside the case on a short cable which works without problems.

  • The DS18B20 are 1-wire sensors, the DHT11 is not 1-wire (it has a proprietary protocol). What connections have you made between these sensors and the Pi? Do the sensors work properly when on a shorter cable? – joan Jul 8 '15 at 21:36
  • @joan I edited the question – qwertz Jul 8 '15 at 21:39
  • I'm not convinced there can be a definitive answer to your question. I'd discount the DHT11 humidity as being a problem. You might have to experiment trying different pull-up resistor values for the DS18B20s. Perhaps try 4k or 3k3 instead of 4k7. – joan Jul 8 '15 at 21:59
  • I am already using a 2k5 and it seemed to work fine, till 2 days ago. – qwertz Jul 9 '15 at 7:51
  • 2k5 seems low. Some people put 4k7s on either end. Frankly it sounds like you have a signal conditioning problem, to do with the length of your cable, it's type, shielded, non-shielded, its capacitance, etc. etc. You might be better off asking on electronics stack exchange as I suspect the Pi is irrelevant to the question. – joan Jul 9 '15 at 8:09

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