Simple CMOS FSK modem

This project is about 4046 PLL base simple FSK modem. Under given configuration this modem send digital signals over two frequencies and which is switching around 378kHz and 226kHz. In this system, modulator uses VCO of 4046, and demodulator is based on close loop mode of 4046 phase comparator and external LPF assembly.

This FSK modem is specifically design to transfer digital signals over mixed signal lines and it can directly use with any slow digital interfaces like UARTs. This system operates reliably under 10kHz range and we test it with standard TTL inputs.

1kHz Input signal and demodulated signal

1kHz Input signal and modulated signal

The given PCB of this system is based on SMD components but it can also construct using standard through-hole components.

During our prototyping we test this system with ATmega series microcontrollers and TTL signals sources. Because of 4046 CMOS implementation this unit can operate in between 3V to 12V by without using any external regulator(s) or level shifters.

Schematic diagram and PCB design patterns of this project are available to download at google drive.

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