I'm working on a project that requires me to wirelessly transmit analog information over a short range (few meters at maximum) to a receiving end from two transmitting ends. The tricky part is I can only use one receiver and I have to build these transmitter-receiver parts from scratch, meaning no microcontrollers or ready-made modules (like those 433MHz RF transceivers that I see commonly used).
I want to use IR or LASER LEDs for this purpose but am unsure how that would turn out. What kind of output would I observe from a photodiode if I were to shine two LASER beams on it simultaneously? For instance, if I were to drive the two LASER diodes with PWM and have a significant difference between their frequencies (5kHz and 100kHz for example), would I be able to filter the two transmitted signals using basic filters with corresponding center frequencies on the receiving end? I don't need extreme precision, as long as I can compare the amplitudes of my original signals on the receiving end I'm good.
I realize that with this kind of set-up the best method would be time division multiplexing but I'm unsure how to achieve that with analog circuitry.
Would you guys suggest any other method for this type of wireless communication? I don't think I have enough experience with electronics to build my own RF transceiver but if you have any tips on that it would also be appreciated. Thank you!
Best Answer
I think you are almost there with the pwm idea. Keep the pwm modulation at the same frequency and then take the output of this at each transmitter and use it to modulate a much higher carrier frequency, different in each transmitter. Filter the two carriers at the receiver and you end up with two PWM modulated signals.
As long as you are not saturating the photodiode the received signal should be the sum of the two incoming signals.