Thanks for the help with the op-amp question earlier. My dad wants me to make an application for him to detect a yellow warning light turning on. The light might be around 30-40ft away. Can anyone recommend a place to start to find a device that will detect the light?
Thanks
Toby

 

A photodiode or a phototransistor with the proper wavelength of maximum sensitivity can do the work.

 

A photodiode or a phototransistor with the proper wavelength of maximum sensitivity can do the work.

These sensitivity ranges are quite broad, however. For a specific color, the best way is to use a color filter or gel. (Of course this should fall inside the sensitivity bandwidth of the diode in use!)

eric

 

As ambient light could cause false detections, I would recommend adding some sort of reference signal. It can be from an unfiltered signal or signal from a different filter. Basically, you would look for a change in the ratio of your yellow light detector to the reference signal.

John

 

I may be out in left field here, but could one use a 30 - 40 ft cable & use the light's voltage to trigger a second indicator?

 

And for a really weird idea, a photo detector in a black tube (think telescope), with a prism in front. The prism will bend light according to color, the black tube will filter ambient out. A mechanical approach.

 

If the light is in a static situation - not a traffic light, for instance, then any detector close to the lamp will work just fine. Shield it from ambient, and the only light it can respond to is that warning lamp.

 

I assumed it must work day or night. The yellow part of the spectrum is pretty prevalent in daylight. Any sort of single-beam detector, whether it uses a gel filter, prism, or grating, will be affected by that. John

Edit: The reference beam also is a type of failsafe, should something obstruct the shielding tube, such as a bee or wasp hive, large truck, etc .

 

yellow warning light

Does this imply that you have control of the warning light?

If so can you mount a small detector immediately in front of it, shielded so that it only sees the light (or abscence of it) from the lamp?

Upon activation the detector could then transmit a signal by various means.