IR Multi-Position Switch

Published:2011/8/12 2:12:00 Author:Amy From:SeekIC

Peter Verhoosel

This multi-position switch is operated by the IR transmitter with HT12R described elsewhere in the issue.

The signal transmitted by the transmitter enters the circuit through infrared detec­tor IC4. At the output the demodulated signal is available, that via R2 and Tl is routed to the input of IC1 (decoder type HT12D). Like the encoder IC, this IC has already been described in Eleklor Elec­tronics on multiple occasions and we will therefore not describe it again here. On the PCB the address lines of IC1 are by default connected with a thin trace to ground. The default address is therefore zero. By cutting the trace with a sharp knife the corresponding address input can be made logic high.

This change of address is only necessary if multiple transmitters are active in the same house.

When the programmed address code cor­responds with the address code of the IR transmitter, pin 17 of IC1 will be high for as long as the transmitted signal is avail­able. LED D4 will light up.

This pulse is presented to the clock input of IC3, a decade counter. After each pulse the decade counter will make the next output high and the previous output will go low again.

When the power supply is switched on, C4 and R6 ensure that the IC is reset; the first output is high and all the others are low. This is the reason that relays are con­nected only from the second output onwards.

After the first pulse is transmitted, Rel will be switched on via R7 and Tl. The next pulse causes both Rel and Re2 to be switched on. After the next pulse only Re2 will be on.

The reset-input of the decade counter is connected via D3 to output Q4. This causes the switch to return to the rest posi­tion after the next pulse.

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