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Hi I have some devices which need to be monitored. So I thought why not using my arduino.
First the device I whish to monitor cant be dissassembled due to warranty issues. It gives it status by two bicolored(Red/Green) LEDs.
Green means everything is OK. Red means something went wrong and needs to be fixed asap. and off means device is off(which might be bad during working time).
My first idea was tojust check for red by gluing a spectral filter over the leds(no idea where one can get such a thing) and gluing a fotodiode to it.
The Problem is that with this idea I can't get the green status anymore.
has anyone an idea how to fix this Problem.

My second Problem is that I got a bunch of those devices which need to be monitored scattered over an area of 15*6meters so worst case scenario would be a sonsor cable with a length of 36 meters.
Is it possible to read a photodiode over a 36meter cable?

The third problem I need to check the status of 42devices with 2 bicolered leds each. I dont think that is even possible with one arduino duemillanov? Or could one use a bunch of shift registers or something similar to make it work?

My Idea to solve the 3 status LED problem is that I heard one could use a regular led as an photodiode. so a red photodiode should give a higher signal when recieving red light.
Is that even true?
If its true one could even use duoleds(green/red) to read the status?

Thanks for your comments and ideas.  

[Reply #1 on:]

2 light dependent resistors with a green / red filter on them to detect the 2 colours independently.