1200 Baud Modem

[yeahbuddy]

Here is a copy of my final project for telecommunications class. Problem is, the old teacher retired and hasnt been replaced and has no current instructor. I wanted to see if I should even attempt such project with my limited knowledge as I do not even know where to begin. So, how would I go about researching and building such a circuit? I do have access to most any commercially available part from school within a reasonable budget.

"The Western Electric 202S and 202T FSK 1200 baud modems use a 1200Hz sine wave (a tone) for logic 1 (mark) and a 2200HZ sine wave (a tone) for a logic 0 (space). Design and fabricate a circuit that will convert a 0.2V peak-to-peak 1200Hz sine wave to -12V DC (RS-232C logic 1) and a 0.2V peak-to peak 2200Hz sine wave to +12V DC (RS-232C logic 0)."

This is all the information given.

 

[(*steve*)]

The naive answer is to use something to detect the frequency, however since there is time for precisely a single cycle during each baud, that's going to be impressively difficult.

Perhaps easier would be to look at the period between zero crossings and return zero if the period exceeds some value, and 1 if it exceeds it.

Alternatively, you could research the techniques used in FSK modems and see if they are applicable to you.

 

[GonzoEngineer]

First, google "Modem IC's"

Then look up the data sheet and see how they work.

Easy!

 

[foTONICS]

What if you used some sort of low/high pass filter to activate inputs whose outputs manipulated NPN/PNP transistors?

 

[Laplace]

Have a look at Cypress AN-2336 "Simplified FSK Detection" which describes demodulation using signal correlation. Seems pretty interesting, and is rather simple to implement.
N2336 - PSoC® 1 - Simplified FSK Detection http://www.cypress.com/?rID=2735