What's Inside: Teardown of a Temperature and Humidity Sensor

[electronupdate]

I bought a "Amsong AM2302/DHT22" temperature and humidity sensor off ebay... all of $4.00.  It works  as advertised and it was very capable for the tiny amount of money involved.

Curiosity got the better of me so I de-capped the part.  It still amazes me how much technology one can buy for so little money... it's basically a little micro-processor controlled measurement unit.

[SeanB]

Very nice, and nice to see the SMD resistor trim as well. You can see it on pretty much any resistor under the black coating as lines. IIRC the larger ones are done by grinding away material with fine silica sand in air blasts or with a grinding wheel, and the smaller ones are laser. Takes a millisecond to read the resistance, and then do a preset one of a few cuts to get the value in tolerance. Then you do a random sampling of them to see if you have the right value spread. Might take a half second in total during production, and you can get a tight tolerance ( and they all will be trending to one side or the other of nominal during a batch) on them. Screen printed resistors that are not trimmed typically have a 10% tolerance in value, and this will vary from each time you swipe the resistive ink across the screen in production.

[rsjsouza]

Good video; thumbs upped! 

[Puch-Maxi]

Thanks for sharing, very interesting indeed!

[T3sl4co1l]

Your voice reminds me of Nurdrage...
What's this?  Nitric (or sulfuric) acid?  Not part of the usual engineer's kit...

Tim

[helius]

Very interesting, and thanks for posting about it.
I was looking at the TI HDC1000 RH sensor, but now it looks like I can evaluate the DHT22 as well.

[Dragon88]

Good video, I subscribed. Thanks.