Impedance value remaining constant after calibrating PMODIA

[hnorth99]

To whom it may concern,

I have been working with the libraries attached below in hopes of getting my PMODIA device capable of measuring the impedance of a simple circuit. I begin by calibrating the device with a reference resistor of 200k. The gain factor is calibrated accurately and the device begins to push out that the measured impedance is 200k. However, when I add an additional resistor (anything from 500 to 5k ohms) in series, the output impedance stays at 200k. This process repeats for whatever the calibration resistor is (if it's 100k, everything reads 100k). I am not sure why this is happening and would appreciate some help. 

Thank you,

Hunter

AD5933.cpp AD5933.h ad5933-test.ino.ino

[JColvin]

Hi @hnorth99,

I haven't extensively gone through the code you provided (and if I'm being honest, I will never have the time to go through this code in the level of detail that would be required), but based on what you are describing it seems like the calibration parameters are getting stored in the device/host board memory and not being updated.

It also looks like the 16-bit real and imaginary data measured isn't converted out of two's complement in the function that reads the data from the registers, which would affect the end results.

Thanks,
JColvin