I'm being asked to make some replacement FSK modems for a system I designed about 30 years ago... not much money to be made, really just a charity job. I originally used the XR2206 as the transmit oscillator, and they are gone. Well, Mouser has one piece for $83. MAX038 is gone, too. Jameco has some 2206 DIPs, which I could scoop up, I guess.
Anybody know of a classic analog sinewave generator chip? A uP and DDS would be a lot of hassle. And I'd like to be able to set the mark/space frequencies with pots.
I guess I could make a triangle oscillator and sort of bend it into a sine wave. THD wouldn't matter much.
The receive direction is easy. I'll use my almost-famous dual tach circuit
with a decent output filter and a comparator.