Hello, I want to passively read the status of of a green LED on a product I own. The green LED is always on, blinks every second or so or is off depending on the status.

I am contemplating whether to use a phototransistor or photoresistor that best picks up wavelengths in the green spectrum. Also, I'd like my detector to be able to pick up the status from a distance away (say a foot of distance).

If up close, I don't think this would be a big problem but I would like to be distanced as much as possible so that it doesn't affect the look of the original product.

Do you have any suggestions? Thanks!

 

Is it not an option to wire directly in to the LED and run wires out from the case? Or would this ruin the look too much?

 

It is a little known and used fact that LEDs also act as weak photodiodes.

You can use a Green LED to detect green light. When lit by a green LED, it acts like a photodiode, though only passing a few microamps. Simply set the LED up reverse biased and it reacts to emissions mostly in the color of the LED (it will respond to a bright enough red LED).

I'm not sure what distance away you are looking for. If it is more than about 1", you may need to use a more advanced system, such as a color video solution. Shorter distances, a photo-resistor with a green filter over it may work, but react slower.