Hi there, I seem to have a feedback loop on my electronics that seems almost impossible but is REAL.
My Laptop outputs via USB to Arduino (normal)
My Laptop outputs via USB-Serial to Plotter (okay), but then
Plotter outputs to LED (hacked) so that it outputs to Aduino (digitalread)
The whole circuit fails at this point: It seems to go Laptop USB1 to plotter to Arduino to Laptop USB2
It's amazing that the laptop doesn't seal the two USBs but I promise that's exactly when it fails. Any help would be appreciated. I kind of need all those connections together but somehow have to isolate the circuit.
From what you have said it sounds like the arduino does not sense the output from the plotters hacked led( turned into a digital output) even though you have the 2 usb cables going into your laptop(to complete the circuit).
Take an ohmmeter and measure the resistance between your plotters ground and the arduino ground with and without the usb cables and do not have anything turned on when doing so.
To complete the circuit you need to have both devices having a common ground.
Thanks for the response. My problem is the opposite though.
I did NOT want there to be a closed circuit. And was hoping that the pc-arduino relationship, and the arduino-plotter, and pc-plotter would all be separate. Unaware of each other as it goes.
But solved this by using a Phototransistor between Arduino and Plotter.