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Topic: Need help with analog input for AttoPilot voltage & current sensor (Read 2 times) previous topic - next topic


OK - I had some time to test tonight.

I checked the voltage between the AttoPilot ground and the actual ground wire that plugs into the power supply - its around 2mV.
Then I checked the voltage between the power supply ground wire and the USB shield wire - about 7mv.  This is with the arduino disconnected from the AttoPilot sensor (because it could mask the ground loop).

THEN... I checked the voltage between the power supply ground wire and the arduino ground - and its 32mv.  YIKES!  And this makes no sense - I thought the USB shield and the ground should be exactly the same, but I guess not!

I took a wire with alligator clip ends, clipped one to the main ground wire, and another to the arduino ground pin, it drops the voltage difference down to 2mV.  When I do this the accuracy of the reading gets better, though.  Actually power supply usage is around 1.2A (I removed some stuff from the PC to make sure they weren't causing issues) and when I connect the ground wire the sensor reading goes from 0.4-0.5A up to .7-.75A.

Actual sensed voltage on the arduino is now 0.03v, my multimeter on it says 0.033v.  The expected reading should be more like 0.045mv, so it definitely now seems like the ground issue is resolved, but I think my AttoPilot sensor is bad. :(


With such small voltages, the AttoPilot could be less accurate. It is probably okay.

Even the Arduino's 1.1V is not exactly 1.1V. If I use an Arduino only at room temperature, I still have to change my calculations, to adjust for a slightly different internal reference.

Do you have a very good quality multimeter ?
The very cheap multimeters could be off by 10% or 20%, and even the average quality multimeters are not accurate to the last digit.

At least you found the problem. How will you solve it ?


Hello guys,

I just received my Arduino Uno and I wanted to make a curent monitor (i also have the LCD16x2) using the AttoPilor 90 Amp sensor which I had from another project.

I wanted to calibrate the code I'm using as the values don't match with the ones I measured with my multimeter, but I noticed something weird, if I power the board using the USB there are some values and the LCD looks ok, if I power the board from a 6v UBEC the screen leters look very dim and the shown voltages are higher ?

Why the values are changing when the power source is changing ?

Thank you .

PS. This is my first arduino project.

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