Monday, 16 June 2014

Problems with DHT11 Moisture sensor

I've recently been playing around with the DHT11 1-wire temperature and moisture sensor for my Arduino, and you may have seen my posts on www.hackaday.com and my old blog.

Now as an update, the DHT11 has burnt out! I was starting to get fewer and fewer readings, getting a checksum and then timeout error from the arduino code I was using. Eventually I never got any returned values, so decided to take a look. After checking all the cable runs, etc, I then added the pull-up resistor that was recommended in some locations. But unfortunately still nothing. So I decided to prise open the little blue plastic package, and the problem was quite clear:


If you look, in the lower left corner of the small coil (?) you can see the burnt parts which seemed to have made contact with the lower circuit board (where the spare leg was) and caused this burnt look. I'm not sure how or why this happened though.
My best guess is a large amount of moisture gathered, condensed and the water droplet caused the short to take place and kill the sensor.

So I've now got a replacement DHT11 and trying to work out how to safeguard the next one against damage and how to better sense the moisture in the dryer without destroying the sensor too!


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