AnsweredAssumed Answered

Input Capacitance range extension  for AD7745

Question asked by Ben24 on May 11, 2015
Latest reply on May 14, 2015 by EricC

Hey,

 

For a current project I am trying to measure the capacitance with the ad7745. The capacitance has a base capacitance of about 150 pF and changes approximately +/- 50 pF. A bit of googling led me to the circuit note CN-0129 http://www.analog.com/en/circuits-from-the-lab/CN0129/vc.htm . I build the circuit exactly as described in the circuit note and attached a fixed capacitance of 150 pF for testing.

 

I have the following problem:

 

I try to read out the I2C Bus with a Arduino Nano board. I'm able to read out the data and display it in the serial monitor, but I allways get a full range output.

How can I tell the Ad7745 that I use a range extension to read out the right values.

 

Does anyone of you have an example program for the arduino?

 

Thanks a lot, I hope anyone can help me.

 

Regards

 

Ben

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