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how to build a sensor/receiver that revives green and red light? Answered

hi guys
i hope you can help me out. i am competing in a roborace (www.roborace.co.za) 
we need a sensor that picks up a green light so that the car can start moving forward,
then we also need a sensor that picks up red light in order to stop the car.

i know you can use a normal LED and connect it the wrong why around apparently  it can pick up the same  color as what the LED is emitting 
example: Green Led will pick up green light.

can someone please help me out

Kind regards 


Lego NXT systems use a colour sensor.


5 years ago

If this is a Day-Light or warehouse-light
What are you going to do about IR ( Infra-Red ) background light scattering
which affects all semiconductor photon sensors
ie any PN junction is IR sensitive.
There are IR filters that can be scavenged from old video cameras even
screen monitors.

Use a tube with the sensor at the far end and aim it where the light
is expected to be.


I think inexpensive color detecting sensors exist, in module form, and the following link points to one of them:

SparkFun - Color Light Sensor - Avago ADJD-S311-CR999

Aside from that link, I have no advice on how to set up your optics; i.e. how to set up collimators, or lenses, to get the light from the object you want to "look at",  into this sensor, or how to make sure that light is the proper intensity.  Also I have no advice on how to actually get this sensor to work with your microprocessor, be it a Arduino(r), or whatever. 

Basically I just found that link, and I am passing it along to you, and whoever else reads this question. Hopefully the data sheet, application notes, etc, can offer those clues needed to actually use the darned thing.

Wait, are you serious about the backwards LED? This could change everything...

What you could do is use two phototransistors, each in their own Darlington pair, with a filter over them so they can only see their respective colors. Then connect each pair to an input on whatever controller you're using, and have at it. Good luck.

Use photodiodes with red and green filters. The LED effect is pretty small and you ain't going to have much light to sense.

thanks it makes better sens too use the photo diode. do you connect it the same way you will make a IR sensor? (the same schematic?). can i use the same resistors and everything what i used for the ir sensor?


Use a little amplifier after the diode - take a look on line for some ideas.