I want to be able to send a modulated signal with an led (or laser) and then detect it with a photosensor and demodulate it. I will only read the intensity of the reflected modulated light, no need to send complex data or signals. There will be several of these signals so they need to use different modulated frequencies so they don't interfere with one another.
Is there some kind of simple demodulating circuit I can use with arduino? Whenever I search I just find examples using the 38khz IR sensor used in TV remotes. This is close to what I need but I need to able to use different frequencies so I can detect multiple signals at once.
Preferably I want to use visible light but IR may be ok.
If you are interested only in the intensity of the beam, and you need to distinguish between several beams, you send each with a different frequency and measure that. There is no modulation or demodulation of the carrier frequency as in lR data transmission. I’m assuming that, any one time, only one beam will be sent.
There are plenty of examples of frequency measurement sketches. Some count number of waves in unit time. Others measure the interval between two pulses.
However, if you are altering the frequency simply to distinguish the sender, this may skew the results of the intensity measurement. Clearly, a continuous beam would be the strongest.