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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

CIRCUIT OPERATION

A Sharp GP1U52X infrared detector module was used to detect the signals from the hand-held control unit. It operates from a 5-VDC power supply, and its serial digital data output is fed directly to input bit 7 of the Stamp. Itýs important to remember that the metal case of the GP1U52X module must be grounded to minimize interference from stray radiation.

After software decoding the transmission, the channel number selected is placed on output bits 0, 1, and 2 of the Stamp. This data is latched by a 74LS175 Quad D flip-flop using a clock pulse generated on output bit 3 of the Stamp.

The latch was included for the following reason. When the system is in scan mode, a delay of 3 s between channel changing is implemented. This may be changed in the software. The Sleep command is used to achieve this delay. However, when the Stamp executes the Sleep command, it momentarily places its I/O bits in tristate mode (approximately every 2.3 s during this delay). This produces a noticeable transient flicker on the display. To eliminate this, I had to isolate the Stamp I/O bits using the latch. If you can live with this flicker, the latch may be eliminated with a small reduction in software size and component count.

The outputs from the latch are used to address the video multiplexer (MAX455) and to drive a seven-segment decoder (74LS48) whose output is displayed on a large (2ý) seven-segment LED digit. This digit, which shows the active channel in use, requires a transistor to drive each segment. I used a hex NPN transistor driver (CA3082) simply because it was available in-house. You may wish to use a display device that doesnýt require external transistors and further reduce component count.

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