Got my IR remote control repeater working, controlling most TV's, DVD, 
etc., but ran in to an issue with the DIRECTV receivers. Most of the 
items use approximately 38 KHZ modulation that is pulsed for varying 
periods. The receivers use no modulation, just pulse the IR signal. Also 
the signal is inverted.

I use the Vishay TSO4840 IR receiver modules to detect the IR signals. 
They remove the modulation and output a clean TTL signal, filtering the 
signal to minimize interference from sunlight, lights, etc.  These work 
fine in all cases, even if there is no modulation.  This TTL signal goes 
to a PIC18F4320 PORTB which then as long as the signal is active (low), 
outputs a software timing loop generated 38 KHZ square wave modulation 
through PORTA to IR LED's to control the equipment.

How can I detect the presence or absence of the modulation with the 
4320? Shouldn't need a lot of detail, but more a direction to head.

My thinking is to replace the TSO4840's with plain IR detectors so the 
modulation gets to the 4320. I need to do more work in this area, to 
insure that there are not range or interference issues. I think range is 
going to be an issue, unless I amplify the signal, though. I use 
Audacity, an audio editor with a plain IR detector as a cheap 
oscilloscope to view the signals. It has been adequate for development 
so far. Wished I had a nice scope but can't justify the  cost at this 
time. The signal generated just with the detector needs the remote 
control to be very close (< 2") to work.

I do have a PICKIT 2, but haven't figured out how to use the logic tool. 
The board doesn't use PGD or PGC for anything but programming. I tried 
jumpering those pins (one at a time) to one of the output pins, and 
changed the software to provide a continuous modulated output signal. 
Triggering seemed to be an issue.

Thanking ahead of time for help. :)


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