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Is it possible to send different signals to a receiver using FM which then the receiver would be able to distinguish between and do a set act based on the signal? How to?

For example, the transmitter gives a sine wave that could be 1 kHz, 2 kHz or 3 kHz and the receiver receives it and enables the corresponding transistor.

Also I don't want to use microcontrollers.

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  • \$\begingroup\$ Yes, this is quite possible. \$\endgroup\$
    – Andy aka
    May 15 at 15:31
  • \$\begingroup\$ @Andyaka oh well, how? \$\endgroup\$
    – adam_Barfi
    May 15 at 15:50
  • \$\begingroup\$ @adam_Barfi adding your "how" question from the comment to your actual question text; your question only asked about whether it's possible. \$\endgroup\$ May 15 at 15:55
  • \$\begingroup\$ Sounds like a job for several LM567. \$\endgroup\$
    – Jens
    May 15 at 19:13

1 Answer 1

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Is it possible to send different signals to a receiver using FM which then the receiver would be able to distinguish between and do a set act based on the signal?

Yes. Any FSK device does that.

For example, the transmitter gives a sine wave that could be 1 kHz, 2 kHz or 3 kHz

That's a 3-FSK. (and that's a bit of an unusual FSK, because in a binary world, it has three possible values, but you can certainly make use of that for channel coding or similar reasons.)

Also I don't want to use microcontrollers.

You're free to do this in whichever way you want, but everything about your problem:

  • Discrete values
  • Changing at times
  • Controlling something in a binary on-off fashion
  • low bandwidth

screams that by far the easiest solution here would be to attach a microcontroller's ADC input to the output of an FM demodulator, or if your 1,2,3 kHz are just electrical baseband, to directly demodulate in software.

But nothing forces you to go the easiest route; you could also implement three bandpass filters (since these are bandpass filters of varying bandwidths, it's probably wisest to go with something like a simple opamp-based Sallen-Key, but the design would really depend on your SNR and acceptable error probabilities), and then use a set of comparators to figure out the strongest candidate (you'll want to have hysteresis, so that your decision doesn't bounce around when you switch from one frequency to the other, or when there's sudden wideband interference). You can then switch the right transistor on and the others off, or whatever you planned to do.

(You'll find that adding safety features, like not randomly jumping between states when the transmitter is off, or holding the last state until a transmitter sends a known preamble to signal that, yes, they're really the transmitter and not just some randomly interfering switch-mode power supply or such, is pretty complicated in discrete electronics, but a few lines of C code on a microcontroller. But I respect your choice to avoid a microcontroller – even if the problem you're setting out to solve (digital control) is literally the thing that microcontrollers are made for.)

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  • \$\begingroup\$ 3 was just a placeholder number I chose, but thanks a lot for your time! \$\endgroup\$
    – adam_Barfi
    May 15 at 16:09
  • \$\begingroup\$ @adam_Barfi you're more than welcome :) yeah, the principle still applies, whether you do 2-, 3-, 4-, 8- or any other M-FSK. You detect the frequency, be it through a demodulator that gives you an amplitude proportional to signal frequency, or through a filter bank, then you clean up your signal as far as feasible, and do a decision on what was transmitted. \$\endgroup\$ May 15 at 16:41

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