Hi, I want to make a data acquisition system with two input channels: CH0 for 4-20mA and CH1 for 0-10V. Both signals have separate grounds, and I want to isolate them from the Arduino's power ground. I’m not sure what keywords I should search for on Google. Has anyone ever made something like this? If so, please tell me how to do it.
Please show more information (circuit diagram) on this essential detail of your project.
If you really want to have galvanic insulated chanals, then you might need to think about two galvanic seperated measurement circuits and optocoupler signal transfer to the central unit.
Maybe I exaggerate with my aproach, but this would be my solution, as long as I have no better knowledge.
To seperate the two chanal measure circuits I would choose some DC/DC converter to power each chanal seperately. (e.g. TMA 0505S)
Then I would design the measuremet circuits, with a controller each. Can be a Arduino nano, seed duino, digi spark, ...
The measured values I would communicate with opto-couplers to the central unit for data acquisition.
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Yes I have.
Do you know how to read a schematic and make a PCB?
These are both effectively voltages, either direct or, in the case of the current measurement, the voltage drop across a resistor.
These can be converted to say a duty cycle of a signal which can be sent through a device (an opto-coupler has already been suggested) and interpreted at the receiving Arduino end.
Here my schematic diagram, B1, VR1 and R1 to simulate current signal 4-20 mA. B3 and B4 to simulate voltage signal 0-10V. I want design circuit that can measure either current signal or voltage signal. in the right side I use volt meter to simulate arduino
Yes I do, usually I use proteus or livewire to simulation and eagle or kiCad to design the schematic and PCB
Do you have any article or example for this method?
Yes I do use resistor to drop the current signal so I can measure it as a voltage. So basically I need to measure voltage signal with isolation grounding from arduino.
I guess you never intend that switches 3 and 4 are never both closed at the same time.
As far as I can see, there should be nothing against it, to put an opto-coupler in between an e.g. UART communication. Probably only unidirectional communication is needed and makes it quite easy. Just a very quick search delivers other ones discussing ...
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Yes, switch 3 and 4 to simulate a voltage signal at 1V and 10V so I can get a picture of the output.
It does not make clear your separate grounds problem. Are the opamps really required for clarification?
You will need to use analog optoisolators such as the LOC110, HCRN200 or IL300. You will also need two isolatod power supplies, one for CH0 and one for CH1.
See the datasheets of the isolators for application circuits.
Is this an academic or theoretical exercise where you have been given, or invented, a rather contrived circuit with 2 separate measuring points identified as A and V and you have to devise a means of presenting their values to an external, isolated Arduino without any mutual interference ?
Alternatively, have you a real-world application where you are measuring sensors etc., with some degree of isolation, and are attempting to find the best way of doing so ?
If it is the latter, then there is surely a better way and maybe say what your requirements are with specific components.
There are many real applications of connecting an Arduino, in an isolated way, to another circuit say, for example, a mains powered device with a transformerless power supply or mains motor controller etc. Your application does not seem to fit this model.
Whatever, maybe this crude addition to your schematic , together with a bit of ohms law, helps to get a common ground between the measuring points:
I don't know if this helps but here is an example of an Arduino communicating a voltage, in a galvanically isolated way, across an optocoupler. The voltage is converted to a duty cycle. It is the opposite direction that you are attempting to achieve but it may give an idea An isolated analog output for Arduino Uno | Hackaday.io
Either the signals are isolated from each other or already have some interconnection. If all cases shall be considered then two fully isolated ADC are required, together with e.g. UARTs and optocouplers to the common base station. Such solutions have been discussed already. Any simplification depends on more/better knowledge of the electrical dependencies between the sensors.
This would work , provided the supplies were all batteries. What would happen in practise is that the grounds would float until they reached a level compatible with each other.
But you are only simulating a small part of the problem, and there are MUCH easier ways to do that - all you need is a battery (to provide the 0-10V signal) and a resistor (to manage the current).
However you CANT use a difference amplifier (IC1) to provide electrical isolation.
Hi, @Hanif01
Before we go any further, can you please tell us what your complete project is?
What are the signals from and represent.
A link to the source of the signals would be very helpful.
Thanks.. Tom... 
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