Brief Background on my project. I have a magnetic pickup sensor: https://www.eddevices.com/Manuals/4.5015U.pdf
that I am using with and optocoupler 817 module since the mag sensor is 12v.
My first question, sorry if its a newbie question, but the mag sensor is already powered and grounded to another circuit and so is the signal out, when i attempt to measure the Hz reading using a multimeter the Hz reading drops to zero as soon as i connect the negative lead to the common ground of the existing circuit, but if I leave the negative lead disconnected and only measure with the positive lead at the signal out pin I can read Hz. Why is that?? I've always been told you need to have a common ground to read a digital signal.
Read the data sheet , again, that you linked to. The output requires a pull-up voltage, see the output 0-10v NPN?
Anything you are getting on your DVM is from the leads acting as antennas.
Why an optocoupler? Connect your Arduino directly to an input-pullup pin and to the Arduino ground and write a program to read the pin and serial-Print the result. Test the sensor with a piece of steel.
The only physical connection between the 7.5-30 vdc is the ground connection. The output means you can apply up to 10 volts. Your Arduino with input-Pullup will apply 5 volts, which is within the 0-10v specification. The device likely already has an optocoupler built into it.
Can you please post a copy of your circuit a picture of a hand drawn circuit in jpg, png?
Hand drawn and photographed is perfectly acceptable.
Please include ALL hardware, power supplies, component names and pin labels.
