Wireless fencing hit detection - sabre

[fencing_n00b]

Hello,

I'm trying to build wireless hit detector for saber fencing consisting of 3 wireless units: two hit detectors worn by each fencer and one hit display (red and green LED). My issue stems from lack of common ground due to it being wireless.
In saber there are 2 isolated metallic areas per fencer: weapon and target. As a POC I need to be able to register hits where weapon 1 touches target 2, weapon 2 touches target 1 and simo where both weapons hit opponents target at the same time.

I came across this promising post:

Wireless fencing scoring system - detecting a PWM signal without common ground

HI! I've been googling for about 2 weeks for a solution to this problem but can't find any practical solution, so I decided it was time to get some help from the Gurus. This is the problem: I need to sense if a PWM signal is present on a metal surface if I touch it with a single wire from a device that does not share the same GND. The purpose of this device is to make a wireless fencing score system. When touching the guard of the opponent weapon that hit must not be considered by the system. …

I reached out to Luis and he is not satisfied with his solution.
luisr320:
"Unfortunately I couldn't find a reliable solution for the lack of common ground problem. After some more testing I found out that the whole blade would be working as an antenna and couldn't cancel the invalid touches."

Also came across this post:

Detecting a frequency signal without common ground

Hi all, I'm sending a frequency signal with an arduino on a output, I want to be able to read this frequency from another arduino with a single pin. I can't have a common ground between them. In the following scheme you can see my idea: the arduino 1 should be able to send a signal trough the connection with the arduino 2 and this should be able to read the frequency. [Arduino-forum-scheme] Is it possible to read the frequency in this scenario or the lack of common ground would invalidate…

and solution given is:

"An optocoupler if used correctly would give a usable signal and fast enough for this application as well. Since it will offer galvanic isolation between both arduinos your situation of not having a common ground would no longer be an issue."

Unfortunately due to my noob Arduino status I'm failing to see how this circuit would be applicable. Can someone ELI5 how and where optocoupler would be useful in this situation?

[anon57585045]

This perfectly illustrates how mere words are insufficient to properly explain a circuit. Without a diagram, it's anybody's guess what they mean.

It sounds like it's taken out of context, from a fuller explanation. Another mistake.

[jremington]

@fencing_n00b

Since it will offer galvanic isolation between both arduinos your situation of not having a common ground would no longer be an issue.

This is simply nonsense.

In other words: not having a ground connection solves the problem of not having a ground connection.

[madmark2150]

Ok, use the inductive tone trick. pump an audio frequency out of each sword. different tone for each. rx mesh has a high gain amp and a narrow pass filter set to the sword tone. Rate of rise and peak of the signal will give you hit info, no common ground needed.