I'm having trouble with this portion of my schematic. The microcontroller that I am using is actually an AT89S52 and everything is done on a PCB all assembled.
What I'm trying to do here is have the phototransistor respond only to red lazer beams (not normal light or infrared). I made two attempts with resistors:
I tried R1=68K, and R2=10K because 10K is a standard pull-up value and 68K because I didn't want detection too picky or too easy. If I made R1 smaller then I probably would detect nothing, but then again, maybe R1 is too small?
So then I tried the new settings of 4.7M for R1 and 240K for R2 so then I can make the ratio larger in hopes that it can detect any kind of light and still nothing is detected.
Now one thing I found out is when I turned my voltmeter on with the new resistor settings and I touched one lead to VCC and the other lead to NPN's collector, the detection takes place.
Before I assume the phototransistor is broken, are there better values for R1 and R2 I can use that would allow the microcontroller to detect when the light changes on the photodiode from super dark to super bright or vice-versa?