The small 8-pin PIC12C508 is pre-programmed to generate our 38KHz carrier frequency by simply pulsing I/O-pin GP1 (shown above).
The PIC will generate either 38KHz or 40KHz, depending on the state of GP3 when power is first applied. If you connect GP3 to ground, then apply power to the circuit, the frequency will be 40KHz. This was implemented for people using the older 40KHz style infrared detector modules. The default is 38KHz with pin #4 (GP3) left floating or (not connected to anything),,,
Pin #7 (GP0) is to inhibit (stop) the carrier output. When GP0 is connected to ground, the PIC will halt generation of the carrier frequency. This is an optional control feature for power saving, and in most cases, un-necessary, but it’s there if you need to use it. Ground pin #7 to inhibit the carrier frequency. Release this pin from ground to start the carrier frequency again.
Connect GP1 (pin #6) of the PIC12C508 to pin #1 of the two-input NAND schmitt trigger as shown in figure 2. The data signal pin can be any I/O-pin from the BASIC Stamp or other microcontroller.
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