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#### cool

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I am a student. I have to do a project about infrared remote control of a wall-switch. It required to fix the frequency of the pulses generated from the IR LED and the receiver can only detect this IR single. :?
I would like to know how to do the frequency modulation of a IR LED? and how to demodulation of the receiver? As only a single switch has to be controlled, I would llike to find the simplest and cheapest circuit to do the project.

cool said:
I am a student. I have to do a project about infrared remote control of a wall-switch. It required to fix the frequency of the pulses generated from the IR LED and the receiver can only detect this IR single. :?
I would like to know how to do the frequency modulation of a IR LED? and how to demodulation of the receiver? As only a single switch has to be controlled, I would llike to find the simplest and cheapest circuit to do the project.

You don't frequency modulate the IR, you amplitude modulate it (at 100%, which means you simply turn it on and off). The common frequency for doing this is around 38KHz, and there are ready made receiver IC's freely available - your TV, VCR, and anything else you have with IR R/C will almost certainly use these.

The simplest way would be to use a 555 and IR LED for the transmitter, and an IR receiver IC for the receiver. The only problem with this is that any IR R/C would trigger it - to avoid this you need to encode the transmitter, and decode in the receiver. Have a look at my IR PIC tutorial at http://www.winpicprog.co.uk which gives details using PIC's, Holtek also make a range of IC's specifically to do this.

"Cheap" method

Try using a DTMF encoder/decoder pair ...

This will give u 16 separate codes....

Big advantage to use a ready-made IR receiver modul as Nigel suggested. But if You need only one command, also useable a low frequency (e.g250...300Hz) on-off modulation of 38kHz, and in receive side for recognization a simple tone decoder PLL LM567.
(I just say this, because cannot programming a PIC...)

thanks all guys!!~
I will try to use NE555 to generate a 40kHz pluses for the tx side and use LM567 to do the decode in the rx side~
hope i can success... :wink:

o... i don't know how to build the circuit for the rx of the remote control when using PIC!
I only have to control 1 switch, any simple common assembly that i can use??
do i still ve to set the frequency by 555 in the tx part????

cool said:
o... i don't know how to build the circuit for the rx of the remote control when using PIC!
I only have to control 1 switch, any simple common assembly that i can use??
do i still ve to set the frequency by 555 in the tx part????

Have a look at my PIC tutorials I mentioned above, I give circuit diagrams, veroboard layouts, and all the source code. There isn't one which does exactly what you require, but it would be trivial to make it so.

Off-topic, but 0mega, did you notice that the circuit in your avatar performs no function whatsoever? It is always off! :?

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