Hi, I'm using a TSOP48 IR receiver (TSOP48 datasheet). I've setup a PIC and IR emitter to output 10 cycles with a 50% duty cycle at 38KHz then pause for 40 cycles (as per the datasheet). I've measured the frequency at the PIC's output pin and it's fairly stable at 38.06KHz during the 10 cycles. The emitter and receiver are about 2.5 meters apart.

The receiver receives the signal perfectly and I can even angle the emitter slightly to the side and it still receives without any issues.

Now the weird part. When I put my hand between the emitter and receiver, the signal stops being received. If I move my hand away *slowly* then the signal is never received again. After cutting the beam off and moving my hand away at medium or fast speeds, the signal will be received again. I'm using this as a realtime beam break sensor so this could prove quite problematic if the beam appears to remain broken.

I suspect the problem relates to the auto gain and filtering circuitry in the receiver. If I leave a 200 cycle pause between each burst then it always works fine but this significantly reduces my sample rate.

Things I've already tried:-
Using 1 emitter
Using 2 emitters
Over powering the emitter(s)
Changing the carrier frequency duty cycle to various values between about 10 and 90%
Changing the cycles per burst. 3-4 seems to be the lowest value that will work at all but nothing up to about 30 makes any difference
Pointing a TV remote at it. It can see the remote fine but continues to ignore my emitter as if it were background noise. I can't reproduce the problem with the TV remote since it has pauses much longer than 200 cycles.