I'm looking at the LM567 PLL specifically. I intend to use relatively low frequencies, 1kHz to 3kHz to demodulate two tone FSK signals at about 1k baud. I see a lot of tutorials out there for generating signals with PLLs, but I can't find much useful on demodulating signals. Example schematics would be useful.
I usually see PLLs used for RF circuits. Is this overkill for such low frequencies? Can the arduino do a software PLL reliably enough? I think this could also be done with high/low pass filters and a few logic gates.
The voltage going into the voltage controlled oscillator is the demodulated signal.
Can the arduino do a software PLL reliably enough?
Yes. There are several other ways to decode FSK signals, and all have been implemented on Arduino. Google "micromodem" for an example.
I think this could also be done with high/low pass filters and a few logic gates.
Of course it can.
It does not make sense to use an Arduino to implement a software PLL for this problem. It can be done but there is no reason for the added complexity of an unnecessary feedback loop. Much better to use an external ISR to measure the period of the incoming signal directly as the time between successive threshold crossings. No feedback loop needed. No need to optimize loop dynamics.