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Topic: Getting an Arduino to Monitor Its Own Voltage: How? (Read 1 time) previous topic - next topic

AdrianLopez

#5
May 08, 2012, 08:39 pm Last Edit: May 08, 2012, 08:44 pm by AdrianLopez Reason: 1

The point is that once you change to the internal referance only voltages below that will be measured, so you have to use a potential divider to do that. Say you have a five to one divider, then exactly five volts on the power will give you one volt you can measure. As the five volt supply changes then so will your reading, because the referance is fixed.


Does this mean I can count on the internal reference voltage not to change even if my Arduino's 5V rail were indeed unstable?

I've measured the 5V rail with a multimeter and the voltage appears to be stable at 4.9V, but I don't know whether the dips and spikes I'm getting are too brief to register on the multimeter.

Grumpy_Mike

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Does this mean I can count on the internal reference voltage not to change even if my Arduino's 5V rail were indeed unstable?

Yes.

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but I don't know whether the dips and spikes I'm getting are too brief to register on the multimeter.

They normally are. However, I am not sure you will see it with the analogue read either, you have to look often to catch brief excursions.

jwatte


The sensor I'm using is powered by the Arduino's 5V supply. What's the reason for dropping the voltage and using a 1.1V reference instead of the 5V default?


Because if your reference is the 5V rail, and if the problem is that the 5V rail is not reliable, then a reading relative to the 5V rail will just follow along with the variations, showing "no relative change."

The 1.1V internal reference is fixed at 1.1V, no matter what the supply voltage is.

Also, just to trouble-shoot your sensor: Try adding a 100 uF or 470 uF electrolytic capacitor between 5V and GND to stabilize the supply, if that's indeed what the problem is.

AdrianLopez

Driving down the voltage to 0.86 volts using a voltage divider and scaling back up to 4.9 in software shows none of the dips and peaks I'm getting with the sensor attached. This rules out the Arduino's 5V rail as being the problem, so either the behavior I'm seeing is normal for the sensor I'm using or else I have a bad sensor. I'll start a new thread in the sensors forum for feedback on the particular sensor I'm using.

Thank you all for your help.

AdrianLopez

#9
May 11, 2012, 10:02 pm Last Edit: May 11, 2012, 10:24 pm by AdrianLopez Reason: 1
It looks like I may have ruled out electrical noise a bit too early: The ADC Noise of Netduino.

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