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QG8 ADC with current sensor help

Question asked by Abhijit Jagtap on Jun 17, 2009
Latest reply on Jul 19, 2009 by bigmac



 I am using a Qg8 with other 5v devices.The simplest & cheapest approach to get 3.3v on QG8 was to lift its ground by 3 diode drops (schem attached)

 I am measuring current with the help of a Hall sensor,which o/p's corresponding voltage(VIOut) scaled to 5v.

 Now the rectified and filtered VIOut is fed to the ADC input.The voltage measured here is some 0.9v w.r.t MCU GND,whereas the current sensor o/ps some 3v.I ask the ADC to take action when this threshold is crossed.

Now I have a question that ,will the ADC consider the voltage at its pins as 0.9v or 3v (with different grounds)..since when i run the code ,the ADC behaves as if the threshold is crossed even when i set the compare value at 1023 (10 bit).

 I dont know if i am clear enough.Please someone reply so that i can take it further.


 Thanks and regards

Message Edited by abicash on 2009-06-17 12:15 PM