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Topic: Temperature Sensor (TMP36) and RFI (Read 836 times) previous topic - next topic

TKHouse

I've been using two TMP36's (https://www.sparkfun.com/products/10988 / http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Sensors/Temp/TMP35_36_37.pdf) recently with my Arduino Uno, works great. The Arduino is connected / powered over USB from my computer (some old Dell Optiplex running Fedora 17).

The sensors were directly connected to 5V from the arduino, ground, and the arduino's analog sensor. Nothing else in the circuit.

The TMP36's have worked without a problem for a few weeks, but after shifting some things around and cleaning up my wiring a bit, I've had some odd results. The TMP36's would suddenly output around .001 to .002 volts from the output pin. I keep my house pretty chilly, but definitely not in the -50 range!

What perplexed me the most was that the circuit checked out just fine time and time when disconnected from the arduino. On my breadboard I could attach a 5 volt supply and the output behaved as I expected. Simply replacing the breadboard 5V and ground with lines from the Arduino resulted in the unusual results.

I dug through the datasheet a bit and noticed a short section about RFI and these sensors. I attached a .1uF capacitor across the supply line and ground and the problem immediately ceased.

I'm curious if anyone has experienced similar problems and what was likely to have changed and caused my sensors to experience so much RFI or if there may be some other factor that the added capacitor would have helped with.

Grumpy_Mike

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there may be some other factor that the added capacitor would have helped with.

Yes it is called supply decoupling and it lowers the impedance of the supply.

JD3

Yup, I learned that one the hard way, too.

.1uf caps are like the magic fairy dust of electronics, sprinkle them everywhere in your design :)
That little black caterpillar you just stepped on will set you back a few bucks....

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