LMC568 replace: PLL, FM-demodulation 82 kHz, how to demodulate

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Joined Feb 9, 2023
I have real-life solution: Door entry system. Communication is FM- of course it found many other functions, but this is only important, FM-demodulation.

Wired communication, max wire lenght 100 meter, so, it is, signal is steady and strong.

Transmitter send 82 kHz carrier signal. This I measure from real life device. Transmitter modulate this with speech, so input is microphone and frequency area is 300 Hz...3kHz.

Transmitter send also special information using carrier signal: switch on/off carrier with 100 Hz square wave and 300 Hz square wave is special information. 100 Hz means "information 1" and 300 Hz "information 2".

Present solution is LMC568 but it family is dead. Present schema is simple: FM-demodulated audio signal go to emitter follower and then audio amplifier. Carrier detect output go to processor: carrier detect, processor switch on audio amplifier. Special information, processor read this carrier detect: "carrier detected" -> audio amp on, "carrier detect make 100 Hz or 300 Hz" -> processor regognize "carrier detect make 100 Hz, 300 Hz". So, LMC568 can follow fastly carrier signal- transmitter switch on/off carrier with this 100 or 300 Hz, and LMC568 can follow it.

So, now I try replace this LMC568 with any other FM-demodulator. FM demodulator 82 kHz carrier for speech audio + carrier detect fast effect.

Looks this LMC-family is quite dead. Eg. LMC567 maybe, it can make this carrier detect, but looks LM/LMC567 is also not recommend for new design.

4046 maybe, 74HC4046 is old but maybe ok. I simulate it with Ltspice, and look it can make fm-demodulation. But carrier detect is not so easy- maybe any rc-filter + schmitt after, but maybe this additional information (100 Hz... etc) make it difficult.

So, I ask ideas. Maybe fm-demodulation must be done with 74HC4046. But carrier detect not so easy. Processor is PIC, so maybe DSP-ideas not work. Also DSP need strong human. I try search also other ideas- discrete demodulators etc etc. I does not fear even coil. Carrier is 82 kHz so it make system same times easy and difficult: demodulators with coils are not so typical. "Typical", with coil are not 82 kHz, 82 MHz... (100 MHz +/- fm-radio), so coil systems are maybe millihenrys.

So, any ideas I ask. "FM demodulator, carrier freq 82 kHz, carrier detect incl this 100/300 Hz possibility, with any solution still available- not obsole components or components will be dead".