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Topic: Safety of going over AREF (Read 548 times) previous topic - next topic

Atomicrox

I have an A1302 hall effect sensor that outputs an analog voltage proportional to the magnetic field. I'm mostly interested on lower field values (of the same polarity) and I'd like to increase sensitivity while decreasing range. I'm thinking about feeding a 2.5V to the AREF pin, which would effective double the resolution over the 0-2.5V range.

My question is what happens if the sensor outputs a voltage higher than AREF on an analog pin - will it cap the value, overflow like a variable or burn the ATMega?
Don't wanna try before asking for obvious reasons ;)

retrolefty


I have an A1302 hall effect sensor that outputs an analog voltage proportional to the magnetic field. I'm mostly interested on lower field values (of the same polarity) and I'd like to increase sensitivity while decreasing range. I'm thinking about feeding a 2.5V to the AREF pin, which would effective double the resolution over the 0-2.5V range.

My question is what happens if the sensor outputs a voltage higher than AREF on an analog pin - will it cap the value, overflow like a variable or burn the ATMega?
Don't wanna try before asking for obvious reasons ;)


Having the analog input pin go over the voltage value of the voltage applied to the AREF pin (and having selected the external voltage reference) is not a problem, no damage, just that any value => then AREF will all return a 1023 count when you perform the analogRead(). The risk of electrical damage is if you have a voltage wired to the AREF pin but then select one of the internal voltage references there is a current path that can cause damage. See the warning caution in the arduino reference section ( http://arduino.cc/en/Reference/AnalogReference ).
Also note that the arduino mega board has a built in internal reference option of 2.56vdc and 1.1vdc while the Uno has only a optional 1.1vdc internal reference.

Lefty

CrossRoads

Don't exceed Vcc by >=0.5V or you risk damaging the pin.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Atomicrox

Cool, that's perfect. I'm using a Mega and that internal 2.56V will do a great job!

Thanks guys!

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