I read something like floating voltage.
QuoteI read something like floating voltage.Yes it sounds like you do not have a floating voltage, you need one to measure it correctly.So more information about where this voltage comes from is needed.What do you get when you measure with your voltmeter the voltage between the arduino ground and each of the two wires you have in turn.
But nonsense value like 0.60-0.70V between + pin and arduino's 0V grnd.
And my ground was arduino's 0V grnd during test. 3V between + and - pins.
I don't understand that.
You can run the arduino off batteries and connect the - to the arduino ground. But then you need an isolated USB connection or serial connection to look at your results on a terminal, this can make debugging hard. .
So earth ground and arduino's ground same thing, isnt it
And just use the rx and tx pins from usb. without any other power connection from usb.
Another way round this is to have a voltage to frequency converter on the plasma end feeding it's output to an opto isolator going into an arduino pin where you measure the frequency and hence the voltage.
Input of optocoupler will be 0-7V analog and you know arduino's analog input's miliamps.
QuoteInput of optocoupler will be 0-7V analog and you know arduino's analog input's miliamps. No you can't transfer a signal in an analogue manor trough an opto as the transfer function is very non linear.You need to change the voltage into a frequency then you send that frequency through the opto. So the frequency you run at is going to determine the opto you need.Something like the LM2907 / LM2917 to convert your voltage into a frequency. This needs powering separately from the arduino, possibly with a battery.
I would use a digital isolator chip such as the ADUM6401, and an SPI ADC such as MCP3201 (or a more expensive ADC with a built-in voltage reference). The digital isolator chip both isolates the ADC from the Arduino and feeds power to the ADC. If you use voltage to frequency conversion and an opto isolator instead, you still need to power the voltage to frequency converter chip somehow.