Acoustic coupler schematic needed

john_s

I plan to use BS2's DTMF for some portable data communication and started looking for methods of acoustically interfacing such devices.·There used to be quite a few acoustic coupler designs in the past but with "all cellular"·they seem·to vanish.·
As I plan to investigate this old method·I'm in search of old·Tandy - Model 100 acoustic coupler schematic (or any 300 to 2400bps acoustically coupled modem's schematic).

Perhaps somebody has such a schematic and can attach an image·of it here... or point out where to find one.

Regards,
John





Post Edited (john_s) : 9/10/2008 5:19:16 AM GMT

LoopyByteloose

An acoustic coupler uses basically a microphone and a speaker to exchange audio with the telephone handset. Since the telephone uses a somewhat limited range of audio, I suspect you can also use a speaker as a microphone. It had been done many times in old intercom designs.

So, you might consider using two small laptop speakers. I have one here that is 8ohm and .4 watt. Added to that would be a good amplification chip for output side and maybe a multiple op-amp chip to filter noise on input side and to increase the input to digital levels.

Try SXList.com or Senix-Ubicom to search for example circuits using the SX-28 chip. They would probably be in modem designs.

You could easily do a direct wiring rather than bother with creating an audio link. There certainly are examples of that. I have a few printouts on file. This SX-28 is the same chip used in many of the newer BasicStamps. The most powerful use the SX-48.

I really suggest you forget the audio link and create a hardware link for an RJ plug. These days, it is more awkward to cradle the handset as standard sizes have all but disappeared.

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