I am using a USB I/O device that allows my computer to detect whether a circuit is open or closed. My computer tracks the status of this input and stores it to a data file. Right now, if there is a bad connection I won't be able to detect it until it's too late and the data has been ruined.

I would like to have an LED that turns on when the circuit is closed, but I can't pass a current through the circuit that the computer is detecting. So, just sticking an LED in the circuit itself won't work.

Is there a simple solution? Can I somehow detect easily the change in resistance when the circuit closes and use that to turn on an LED?

Thanks for any advice you may be able to give!

 

You would need a USB I/O device that allows your computer to detect whether a circuit is open or closed. Then your computer can control the LED.

 

That is how it is set up... but I'd rather not use the LED as a computer controlled output, since it would consume computer resources to run the LED (I want as much accuracy as possible on the detection side). I thought surely there is a way to use the logic of open or closed to control the LED without using the computer?

 

I've attached this drawing, to help with my question. USB device detects open and closed. LED depicted in red. What I need is something like the yellow thing that activates the LED when the resistance is low. Is what I need a simple transistor of some kind? Or does a simple solution (logic based on resistance) not exist?