First of all, let me begin by saying that I'm still pretty much a rookie.

I have a project with a dht21, an LDR and an ultrasonic distance sensor. I have 3 different arduino uno boards, namely:

  • A (supposedly) original arduino uno r3.
  • A chinese nhduino, arduino uno r3 clone.
  • And this one, sitting on top of this.

I've been playing around with the three boards for the last couple of months, testing a variety of sensors and having the same results with the three boards, as expected. But then, with the aforementioned setup, I'm getting very different readings on the DHT21 sensor. If I use the "regular" (first two) arduinos plugged in my laptop, the readings are consistent. But if I use the banana pi(duino), I get the temperature reading correct, but getting weird humidity readings... pretty most of the time a 5% humidity value.

Everything tested on the same room, same sensors and same protoboard. No external power supply.

I'm totally clueless here, any ideas of what could be the problem?


  • Do you have multiple DHT21's as well as multiple boards? If so, I assume the error still follows the board, not the sensor. Is there another library you can use on the RPI, or maybe take the Arduino piece out of the loop, and interface the sensor directly with the pi. Lets try to figure out which component is giving us the issues. (Sensor, Arduino, Pi, or code)
    – Butters
    Mar 19 '15 at 15:45
  • Only one DHT21, one LDR and one Ultrasonic. Same board, I just plug/unplug jumpers cables. It's not a software problem either, as the BPiDuino has been working like a charm so far with every other digital or analog sensor I've thrown to it. Except for the DHT21. But I think I've found the solution, because now I'm using a breadboard power supply and it's working no matter whether I power the PSU from the banana pi USB or from the barrel jack. Mar 19 '15 at 16:14

Problem solved. Using a ywrobot breadboard PSU and now it works. I haven't tested current in the circuit but looks like it was just too low. I wish I'd had datasheet for the board to look at. In a language different from chinese would have been ok, I guess.

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