How to Demodulate Binary-FSK (BFSK) Signal in Proteus

To demodulate an FSK signal in Proteus virtually, first we have to build a design (.dsn) file in ISIS. ISIS is the circuit/schematic drawing & simulation tool of Proteus of Labcenter Electronics. Here is given a full guideline and also the ISIS design file of Proteus. It is not customary here to discuss how to use ISIS.

Here, we are given an audio file which contains the binary data modulated FSK signal. And we have to demodulate the signal to show its message on virtual terminal.

To modify this design for your needs you need to know few parameters. They are:

  • Mark frequency: To design Mark frequency filter
  • Space frequency: To design Space frequency filter
  • Baud rate
  • No. of data bits
  • No. stop bit
  • Parity condition (if any)

The design, that is implemented here is shown in the block diagram below.


In the FSK signal that we used:

  • Mark frequency = 950 Hz
  • Space frequency = 750 Hz
  • Baud rate =50

And the FSK demodulator design looks like below in Proteus ISIS.


We used Multiple-Feedback Band-Pass Filter in this design. Modify the parameters to your needed frequency. You can find details about it on internet or on Electronic Devices of Floyd.

The Peak/Envelope Detector consists of a diode, capacitor & resistor. Value of R & C (RC time constant) is measured by the law:

1/Baud rate = R×C

But, I kept RC constant below of the inverse of baud rate which gives higher roll off rate. I used 1/(2×Baud) = RC.

Finally, right click on Virtual Terminal, go to Edit Properties and put the value of baud rate, data bits … in the properties of virtual terminal or leave default. Virtual Terminal is in the list of Virtual Instruments Mode and the output is to be connected to the RXD pin of it.

Now, here is the Proteus ISIS design file with the BFSK .wav sound file. Remember that you have select the location the file from the properties of the input signal in ISIS. Otherwise input isn’t there and simulation wont work. Download link is given below.


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