IR REMOTE-CONTROLLED VIDEO MULTIPLEXER

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IR REMOTE-CONTROLLED VIDEO MULTIPLEXER

Lessons from the Trenches by Peter Gibbs

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

THE MULTIPLEXER DESIGN

For the video multiplexer design, I only required buttons 0 through 7 for 8-channel selection, and I used the memory (Mem) button to start the scanning mode. Close examination of Table 1 shows that, to decode a specific button from among the nine buttons, only bits 1, 5, 6, 7, 9, and 10 are required (bit 7 is retained for decoding button 1, see Table 2 and Figure 2). All other bits were identical for this button group.

	Bitstream
Key	1	2	3	4	5	6	7	8	9	10	11	12
0	0	0	0	0	0	0	1	0	1	1	0	0
1	0	0	0	0	0	0	1	0	0	0	0	0
2	0	0	0	0	0	0	1	0	1	0	0	0
3	0	0	0	0	1	0	1	0	0	0	0	0
4	0	0	0	0	1	0	1	0	1	0	0	0
5	1	0	0	0	1	0	1	0	0	0	0	0
6	1	0	0	0	0	0	1	0	1	0	0	0
7	1	0	0	0	1	0	1	0	0	0	0	0
Mem	1	0	0	0	0	1	1	0	0	0	0	0
Table 2ıThe bitstream pattern of the nine keys used in the final design can be seen here.

Because of the simple software decoding scheme I used (although the memory button is used for selecting the scan mode), any button not decoded will initiate this mode. Note that, depending on the UIRC used and the protocol of the manufacturer, the count values mentioned above will vary. Also, using a faster microcontroller would require a 16-bit variable because the count could exceed 255.

Figure 2ıIıve provided the logic equations used in Listing 2 to decode the nine keys from Table 2.

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