Hello I have been trying to build my own job site laser grade receiver. The transmitter laser spins at 600 rpm, and so to a receiver it appears as pulses. I do not understand how commercial off the shelf receivers filter out direct sun. My system uses the lm567 tone detector with a photo-diode, (which idea I got off this forum) which feeds into a propeller so when the beam is spinning across the photo-diode at 36khz it triggers and the propeller reads the pin from the lm567. It works well inside, but as soon as the sun shines on it if floods the photo diode and it quits.
Does anybody have any idea's how the professionals do it? Judging by my amateur receiver's performance their receivers are almost miraculous as they perform perfectly on a wide open job site in direct sunshine all day when mine fails if indirect sun bounces into it! I am going to try the circuit attached which apparently is very famous and is on the Mars Rover, but it seems to me the fundamental problem is that in direct sunlight my photo-diode is just completely on. Besides, my part count for 5 photo-diodes would be quite large since i would have to do one of these on every photo-diode which would be 4 extra transistors for each photo-diode and when i look inside a commercial laser receiver i do not see that they did it this way with so many parts. But I am not knowledgeable enough to reverse engineer their multi-layer pcb. . If anyone has seen a rotary laser receiver they would also see that the diodes are pretty exposed, with the filtering only being a red plastic film. But I have seen one guy grading with a receiver where the film was scratched away multiple places and his system didn't seem to mind!
My own thinking is that it has something to do with the rotary laser spinning so it is pulsing the receiver, so the receiver is designed to be triggered by a pulse and ignores the very strong DC offset caused by the sun, This seems to be confirmed as if I shine a laser pointer at the receiver it does nothing, but if I wave it quickly back and forth it responds. This is good but it destroys my system with the lm567 as I need an exact frequency of pulses whereas all the commercial stuff just needs a repetitive pulse of any "reasonable" frequency. This is a great mystery to me that I have been thinking about for a while and searching on Google on and off for pulse receivers, infrared pulse receivers and getting nowhere, any insight and knowledge from the experts on here about how this is done, would be greatly appreciated. I have included links to a commercial laser receiver so one can see what they look like.