pin interrupt for signal with isolated GND

[i3dm]

Hello,

i have a system that reads RPM via hall sensor connected to digital pin which trigges a pin interrupt and counts the time frame.

my issue is that the hall sensor has a seperate GND from the arduino, and i do not want to connect them together as the hall sensor side is noisy and might hurt system peformance.

what would be the best way to trigger pin interrupts of a signal without combining grounds? maybe connect the hall sensor GND to analog input in the arduino and somehow trigger interrupts based on voltage difference between the hall signal and hall GND?

any advice would be appriciated.
thanks.

[dougp]

Optocouplers are commonly used for galvanic isolation.

[i3dm]

Thank you,
im fimiliar with optocouplers but trying to find a SW solution before i go to additional HW.

[Smajdalf]

Will connecting grounds only introduce noise to the circuit? Anyway you can connect them via a resistor or a choke to block the noise?

[SteveMann]

Often, connecting a common ground reduces noise.
Of course, if you post a schematic (not a pretty Fritzing image), you may get more and more appropriate answers.

[i3dm]

i do not have an electrical schematic, but made this block diagram for reference.
i can answer any questions.

[Paul__B]

Well, it is either an optocoupler or a transformer.

[SteveMann]

i do not have an electrical schematic, but made this block diagram for reference.
i can answer any questions.

Your drawing if far superior to a Fritzing picture.

What is an F.GND?  None of my arduino boards have a pin labeled "F.GND".

[i3dm]

sorry. f ground is a floating ground / isolated. it is the ground coming from the CDI which i wanted to isolate.

[aarg]

Sorry, but this simply won't work. It pretends that electrons behave other than they actually do.

[SteveMann]

sorry. f ground is a floating ground / isolated. it is the ground coming from the CDI which i wanted to isolate.

I don't see any need for a "floating ground", which is no ground at all.  You show it going into the Arduino (which one)? What pin?