I'm getting back into electronics as a hobby after many (too many) years, and my knowledge wasn't too great back then. So please excuse any misunderstandings on my part.
So I have a Pi Zero W, and I want to use it to send me the trigger time of a broken laser beam. I have the laser control side already, and the software is not an issue for me (I'm in IT). And, I have developed a basic circuit that will give me laser on/off input on a single GPIO, and abiltiy to turn the laser on/off through a GPIO output. The circuit uses a Photodiode and an NPN transistor and a couple of resistors and works well - in lowish light. The laser will be bounced off of a retroreflector.
This setup will be used in full daylight. I don't want to use Infrared because I have seen similar systems perform very badly in full sunlight. Obviously the PD will be shielded and baffled, but I'm concerned ambient light will alter the floor level of the voltage passed through to the GPIO input, possibly triggering it falsely.
What I would like to be able to do, is adjust for the ambient light. I've been experimenting with a voltage divider network using GPIO outputs to sort of simulate a 4 bit adjustable divider (on a circuit simulator). That way I could flash the laser and choose the 4 bit value that gave the best reading. I've tried a few different circuits to do this, but they never seem quite right, and I'm really just fiddling around without knowing quite what I'm doing. I've also found different advice on what the trigger voltage is - from 0.8v - 1.2v.