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Hi,

I am having a problem getting a correct reading for the voltage.

I am in Canada, with a split phase system at 120/240VAC. I am using a 9.5VAC transformer and voltage divider to reduce the waveform to a readable level for the Arduino Uno board I am using. I measure approx 4.3V P-P AC, with 2.39V DC bias.

I am trying the example Voltage-Current sketch from github. I have the current input pin shorted to ground. I thought I should be able to change the calibration value to change the reading to what I am getting from a Fluke DMM (Model 77). 

With the input pins of the Arduino floating, I had strange readings, probably due to noise pickup. Shorting the Current input pin to ground, and feeding my voltage input to the Arduino corrected most of this problem.

What I get now is '0.00 0.00 0.00 161.7 nan'. I have changed the calibration value for the voltage from 1 to 500, from the value in the downloaded sketch (234.26, I think), but the reading remains the same.

If I unplug my voltage transformer feed, the printout drops to '0.00 0.00 0.00 0.78 nan'.

It seems, since the Voltage reading does drop to under 1, that I am measuring some kind of voltage, but I do not understand why changing the calibration factor does not change the voltage indication. I also do not understand where the 'nan' indication is coming from - should that not just drop to 0 with the input connected to ground?

Can anyone help? Thanks in advance.

Lennard