Would this infrared transmitter - reciever circuit work?

[Resistanceisfutile]

Using a bistable oscillator circuit (using a 555) with an additional set of buttons which each button putting a different resistor in the circuit when pressed (so every button would lead to a different frequency being produced) This bistable oscillator would be connected to an infrared emitting diode.
Inside the receiver circuit a phototransistor would detect the pulses and allow current to flow through reproducing an alternating current of the same frequency inside the receiver. If I used a set of capacitors to filter the frequencies would I be able to make a multi-function remote control?

 

[Audioguru]

The 555 output is a square wave that is full of harmonic frequencies, not just one sine wave frequency.

You need a bandpass filter for each frequency that is not a simple capacitor.
Why not use a touch-tone encoder IC for the transmitter and a touch tone decoder IC for the receiver instead then the frequencies will be accurate and harmonics of them will not cause false triggering.
Touch tone (DTMF) is used for telephone dialing.

 

[betwixt]

Referring to the original post, using different frequencies will work at the transmitter but a simple capacitor filter will not work at the receiver. The reason is explained by Audioguru although why it will fail isn't clear. You have to pick transmitted frequencies which are not harmonically related or appear in background light. For example you can't use 50 or 60Hz because those frequencies are generated by AC incandescent lamps, you can't use twice those frequencies because they are generated by flourescent lamps. You can't use frequencies between about 40KHz and 60KHZ because they are generated by CFL and LED lighting and from what is left, you cant use frequencies that are multiples of each other because of harmonics being generated.

A simple capacitor filter will not be selective enough to pick out the frequencies you want although a more complex filter probably would work OK. It is far more reliable to encode the switch data and decode it at the receiver than to use analog methods of separation and the circuitry isn't much more complicated.

Also be careful to use a wideband IR receiver and not the type used in TV/VCR remote control receivers because they have additional filtering inside them that stops different frequencies being detected.

Brian.