Q 1: IR TX

When build a IR TX board with a PIC with PWM output, is it possible to set
the PWM to 38kHz (or 40 kHz for Sony), and turn the output pin ON and OFF
easy by program?
Or do I have to use this diagram (IR2.gif with NAND gate) to switch the IR
LED ON and OFF. It use to pins but I want to use only one to IR TX.

See IR2.gif


IF the PIC is dedicated to the IR TX task at the time (and it may well not
be) then you could generate the 38/40 kHz entirely in software (about 12 uS
per half cycle so you would really want to be using a faster than 4 MHz
part).

Turning the timer output on and off would work. whether this reduces your
flexibility for some other purpose would be the main consideration.

If you want to switch an external gate then, if you don't want to use an AND
IC, an AND gate can be made with a transistor, 2 diodes and a few resistors
(or even without diodes with a little care with biasing.





        Russell McMahon

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