Data --> Modulated squre wave ???

[mackrackit]

If I understand the project correctly your logic is "OK".

Answer to question #1- Darrel Taylor posted a week or so ago a timer that tested to within 1 second in a 24 hour period. ( I do not have the link, search his post) So the timing can be made accurate enough.

Question #2- I think you will want to use the Hardware PWM and an interrupt.

Sequence of events (Flow Chart )
PIC #1 is using the COUNT command to monitor incoming signal from existing product.
If COUNT does not equal a pulse every 4ms GOTO SEND_RC.

PIC #2 receives signal from PIC #1.
PIC #2 does something.

All the while the radio link is "HOT" so PIC #2 will be receiving data waiting fo a certain command. Use SERIN2 with the WAIT modifier.

We can work on the details some more later if this is all correct.

[RussMartin]

I've worked with RF most of my life, so I have a question or two . . .

What transmitter and receiver hardware are you using?

On what radio frequency?

Since you mention a period of 4 ms, I assume you will modulate your carrier at 250 Hz, yes?

Are you using FSK (frequency-shift keying)?

What is the shortest time period (the smallest window) in which two of the 3 us pulses are likely to occur? Is it likely to be as short as 4 ms?

Is the entire information to be transmitted simply the fact that the 3 us pulse has occurred?

Russ