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IR REMOTE-CONTROLLED VIDEO MULTIPLEXER

by Peter Gibbs

Start ý The Objectives ý Circuit Operation ý Decoding the URIC ý Short Program ý The Multiplexer Design ý Software ý Sources and PDF

SOFTWARE

Listing 2 (IR.BAS) is the final program downloaded to the Stamp. It polls bit 7 for a low pulse to determine if a button is pressed. If no button is pressed, it checks to determine if the system is in scan mode or locked onto a specific channel and then takes appropriate action.

The main limitation of the design was the lack of an interrupt, which would allow instant recognition of button activity. Unfortunately, a button pressed during the 3-s sleep period is ignored. As a result, during the polling stage, you must hold down a button until it is recognized. This is only necessary during scan mode.

To save precious memory, variable b0 is reused as a garbage variable when pulses are read in. Bit values not necessary for decoding are discarded. Finally, it is used to calculate the button value. This value is then stored in variable b3, and the Lookdown command is used to load pins. The statement PULSOUT 5, 5000 beeps a buzzer for audible indication of channel change, and PULSOUT 4,5 clocks the latch.

The complete schematic of the system is shown in Figure 3. I take the composite video output to a small video transmitter, set it to Channel 13, and view the display on a small TV in my office.

For power, I use a standard ± 5-VDC power supply from our digital electronics labs; demand is small and any supply capable of 500 mA will suffice.

I am sure you can improve and simplify my program, which was written to merely get the system operational. Iýve provided a parts list of the items I used in the system. So far, the system has worked, and itýs been in use since August of 1999.

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