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Topic: analogRead fluctuates (Read 550 times) previous topic - next topic

fcady

Hi everybody, I've written a program that constantly uses analogRead to measure the voltage being outputted by a sensor I made.  I am testing the voltage with a voltmeter and it's very steady, but the arduino reading is fluctuating by 0.05 to 0.2 volts around what the voltmeter says.  When I measure ground directly it seems to be fine.  Any ideas what could be the problem?  I tried grounding the analog pins that I wasn't reading from, but it didn't help.  Thanks!

Grumpy_Mike

This is normal. Either put a 0.1uF cap across the voltage input or average ten or so readings.

RIDDICK

1.
the voltmeter averages its readings...
it doesnt update the display 5000 times per second... :)
2.
possibly ur reference voltage is not very stable?
those 5V from the USB are not very stable...
3.
ur sensor might have some noise on the output that u cant c...
e. g. 50Hz/60Hz mains power lines cause some noise...
but 0.2volts (appr. 40LSB @Vref=5V) sounds a little bit too noisy...
-Arne

dhenry

Quote
fluctuating by 0.05 to 0.2 volts around what the voltmeter says.


That's 1 - 4 lsb. Typically a fluctuation of 1-2 lsbs is normal. So yours is slightly outside of that range, which could be due to the sensor's output - put it on a scope for sure.

BTW, the fluctuation you observed is the reason the adc module makes a good random number generator.

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