I wish to make a voltage sensing circuit (range -15V to +15V) using an Arduino's ADC. The problem is that since this circuit will be part of a much larger circuit in which the Arduino is performing many other functions as well, the circuit needs to work both when the Ground of the Arduino and the Ground of the circuit whose voltage is to be sensed are shorted, and when they are not. I do have a waveshaping circuit which works when the grounds are shorted together. Please suggest some circuit or any other way I could approach this problem. The two circuits I have designed can be found at:
!(http://imgur.com/lv0UKya)
!(http://imgur.com/ISq9ou8)
Electronic – arduino – Voltage sensing using Arduino with and without common reference
arduinomultimetersensingvoltagevoltage-reference
Related Solutions
Given your new enhanced description, you should probably be using DIGITAL TECHNIQUES to look for falling edges on your 9V chopped signal. Use the signal to drive the base of a transistor, and a fairly big resistor to current limit that. Power the transistor with 5 Volts.
An optocoupler needs to suck enough current to drive a photoelement, and will probably draw more current than a simple transistor circuit.
Detecting your falling edges is a much more efficient way to deal with all of your issues than sampling of the analog signal.
simulate this circuit – Schematic created using CircuitLab
If you run this simulation, this is actually inverting, so you would detect rising edges. I used a generic transistor, but a 2n3904 would be fine.
Yes, @SHG is right, and you confirmed my suspicions.
The analog input measures the voltage difference between the arduino ground and some point above arduino ground.
You can only measure relative to the Arduino's ground, not measure some other point in another circuit.
You have to connect the ground of the Arduino to the ground of the remote circuit in order to get any form of meaningful signal. In your case you would basically be measuring the Arduino ground since they would both be connected together.
Best Answer
I read the above and the only sensible way to achieve this is to design an isolating circuit maybe like this: -
However, given you want a digital number representing your analogue value inside the Arduino I would go for your Arduino controlling an ADC that is isolated via an isolating SPI interface such as: -
The ADuM5401 is key because it also supplies power to the ADC chip. The ADC chip above is typically an AD77xx type device that comes in several flavours from ADI.