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Topic: [Problem} Voltage Measurment withough common ground (Read 262 times) previous topic - next topic


Jun 03, 2020, 05:03 pm Last Edit: Jun 03, 2020, 05:43 pm by iamsynthetic

I recently got an Electronic DC Load from ebay, and i am trying to implement and arduino controller into it.

The arduino is going to do the following things.

  • Drive the display (planning on an OLED)
  • Display Voltage
  • Display Current
  • Display Temprature
  • Controll a digital potentiometer
  • Dataloging to a pc or SD card.

Currently i am still designing the arduino circuit that is going to sit on a custom PCB.

Now the problem:

I am trying to use an ADC (analog to digital converter) to measure the voltage of the load, aswell as measure the voltage accross a current sensing resistor. The problem is that i need to power the ADC from the Arduino's & Load's power supply, while measuring an alltogether diferent curcuit. I undestand the concept of common grounding, but having measured the Load's Ground and the Load's Load ground (yes, you read that right),i see a 320kΩ resistance between them, and i feel reluctant to merge them without knowing what that resistance is.

The load itself is this one: LM324 electronic load - Xiaolin

Any insight would be greatly appreciated.
Thank you for your time.


If you want to measure the voltage across a load without using a common ground, use a flying capacitor circuit.

You can either use:
a DPDT relay
several H11F1TVM Opto FETs

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This should be what you are looking at but includes a schematic:


In that schematic the load power is AC and rectified on the board and filtered. They do point out "With 12V switching power supply, rectifier can not connect". Which using my Chinglish to English converter agrees with the schematic. So the board operates on 12 VAC. Tells me you will need a mains to 12 VAC transformer to power the board.

As to ground? The load ground would be your common ground.


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