A very simple FSK demodulator for (the 2025 Hz and 2225 Hz) electronic project can be designed using the LM565 which is a general purpose phase locked loops IC containing a stable, highly linear voltage controlled oscillator for low distortion FM demodulation, and a double balanced phase detector with good carrier suppression.
The VCO frequency is set with an external resistor and capacitor, and a tuning range of 10:1 can be obtained with the same capacitor.
As you can see in the circuit diagram, this FSK demodulator require extreme few external components.
As we mentioned, this circuit is an FSK demodulator for the 2025 Hz and 2225 Hz , but you can change the parameters, by changing the loop filter components.
This demodulator circuit needs to be powered from an external 12 volts DC power supply.