How to record serial output to audio file

[gwendalwood]

Anyone know how to record serial output to an audio file and then when the audio file is played on a CD player, the audio is converted to standard RS-232 serial output? I want to take computer created control of a servo controller board and record it so I can play the audio voice on left channel and the serial output on the right channel of the stereo output and and control the servo control board.
George

[dyarker]

What bit rate do you want?

If 300bps is fast enough use an FSK MODEM chip to convert data to audio. This has highest probability of successfull implementation.

1200bps might be done with a PSK MODEM chip.

If you can build your own FSK modulator/demodulator higher bit rates are possible because a CD has an audio bandwidth of like 22KHz, the 300bps chip was designed for phone lines where the bandwidth is only 3KHz.

Trying to use an off-the-shelf MODEM is, IMO, a no-go. Rates of 9600bps, and up, are syncronous between MODEMS even though the RS-232 is async. (2400bps and 4800bps ???) Either way the firmware in the MODEM expects another MODEM at the other end of the audio connection.

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I think I would do this other way around. Instead of changing data to audio, I would store the sounds as .wav files in a laptop or PDA, etc. Less custom built electronics, and easier to change the servo control codes/sounds.

Cheers,

[CeaSaR]

Try searching for "Teddy Ruxpin" or "Teddy Ruxpin Hacks". This animated toy from
the 1980's used the same scheme you are referring to, except it used cassette
tapes instead of CD's.

CeaSaR

[gwendalwood]

I am familiar with the Teddy Ruxpin bear, and it isn't the same. It uses one integrated servo mechanism to move the mouth and it does not appear to be using rs-232 data. I need to control servos from audio. I have an audio to servo controller board, but it only provides on/off positions when sound is present or not present. I need to control 8 servos proportionally as servos are normally used. Any other suggestions?
Thanks,
George

[Fixxer]

Heathkit's Hero 1 robot had a scheme to record programs to cassette tape, IIRC at 300 baud. It would take me awhile to find my notes, however.

I remember using XR2206 function generator chips to implement modemlike circuits back in the 80s- 1125 Hz= Binary 0 and 2250 Hz= Binary 1. We used an XR2207 VCO to decode the tones at the other end.

You might download a datasheet for both, to see if they will work for you.

ETA: I didn't realize that the last post was in June- sorry.