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Author Topic: troubleshoot DHT22 Humidity sensor  (Read 927 times)
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I had one of these running well in a sketch, and then added two more.  At first only the original one of the three worked, then a different one of the three when I swapped the sensor attached to the original pin.  Then they all stopped working after stopping and restarting with a few different pin combinations.  Then I noticed that my +5V was providing 3.8v (from USB).  I added a wall wort and now have steady 5.0v.  There are other things going on in this sketch (Ethernet shield, 12 DS18B20s.)  Now my output from the three DHT22s is:
Code:
Earth Tube Humidity pin25, DHT22, Time out error, Humidity: -999.0%, Temperature: -1766.2 F, Dewpoint: nan F
Outside Humidity pin22, DHT22, Time out error, Humidity: -999.0%, Temperature: -1766.2 F, Dewpoint: nan F
Inside Humidity pin23, DHT22, Time out error, Humidity: -999.0%, Temperature: -1766.2 F, Dewpoint: nan F

How do I troubleshoot the DHT22s?  Did I ruin them with a brownout low voltage?  What exactly does the Time out error mean?

Thanks!
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Without a diagram of how the DHT22s are connected its impossible to answer your questions.
A timeout error means that the DHT22 is not responding to commands from the Micro.
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I used the standard wiring.  10K resistor.  Looking at the data sheet, the DHT22 is supposed to run on 3-5 volts, so brownout on the DHT22 end seems unlikely.




* dhtwiring.gif (20.73 KB, 514x421 - viewed 206 times.)
« Last Edit: July 08, 2013, 11:35:11 am by turgo » Logged

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In theory there is no difference between theory and practice, however in practice there are many...
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from - http://www.micro4you.com/files/sensor/DHT11.pdf - chapter 4:

DHT11’s power supply is 3-5.5V DC. When power is supplied to the sensor, do not send any
instruction to the sensor in within one second in order to pass the unstable status. One
capacitor valued 100nF can be added between VDD and GND for power filtering.


DHT11 is the little brother of DHT22 - same handshake other data interpretation.
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Thanks for the idea.  I added 100nf caps, but to no effect.  How can I determine if these DHT22s are still alive?
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The sensor in the diagram looks like a DHT11, not a DHT22.
The sensors are similar, but the decoding code is not.
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