Thinking about this some more, a Trinket M0 could monitor the voltage of the LED with a GPIO and output it while emulating a USB keyboard. I use trinkets as keyboards all the time. I have a rotary encoder that outputs the AV keyboard codes for volume up and down on my headless pi as an example. They are cheap. Then you need some PC code to read the keyboard and get you the data. It could be done in a web browser to make a status display you could read via VNC.?
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Colin - K6JTH?
Colin Kaminski