Hi All, Anyone tried to use these phototransistors before? I purchased a few from Digikey to see if they would work in a color sensing application I have, and they don't see red! I am trying to figure out if I just can't read a data sheet, or if they have a bad batch of these out there.
I am using it with an RGB LED, and I get fine reading with the green and blue, but I don't see a thing from the red led. According to the datasheets, the red LED is at approx. 625nm, and the phototransistor is supposed to have a better than 80% relative sensitivity at that wavelength, but I am not getting any response at all.
I started with three separate LEDs, but when I didn't get any response from the red, I just assumed that the old little red LED from my junkbox was just not as strong as the new green and blue LEDs I used, I replaced the LEDs, and still had no red. I then replaced the phototransistor, and got the exact same response.
This is for a pretty slow application, and is not designed to be all that accurate, so I was hoping to get away with not needing an opamp to boost the signal, but not getting any response at all in the red is a real killer!