ikalogic said:
hi everybody,
i build this ir based proximity sensor...
all the components are on the same plane, so the IR receiver will only receive IR that is reflected on an object in front or the board..
But the results are not exactly what i expect, the range is really low: only 4 to 5 cm in best conditions!!!
it is strange because i am using 8 IR leds... i dont know weather i have an error in the following circuit or it is impossible to do..?
here is the circuit..
You need to amplify the signal from the IR diode, feeding it directly to a comparator is really going to restrict your range.
You also have a huge problem with external interference, the photo-diode will pick up ambient light and IR as well as the required signal. It's usual to modulate the IR transmissions, and use a receiver sensitive to the modulation frequency - you can get specially designed IR receiver IC's for just this purpose, used in TV's etc.