🚀 go-pugleaf

 
     I've built DTMF decoding circuits for a variety of applications.  The
SSI-202 chip seems to work well.  In fact, I've got one hooked up to a
microcontroller project right now!  By the way, SSI stands for Silicon Systems
Inc.   You might also want to look into Teletone's DTMF decoders.  
 
     For Teletone's number, call 1-800-555-1212 (800 information).
 
 
     As for interfacing the output of one of these to RS-232, you need a UART.
 This is a chip that will take the 4 bit output of the decoder and convert it
into serial information.  There are several of these available.  General
Instruments makes one called the AY-3-1015.
 
     Both of these chips are extremely easy to use.  However, you might have a
problem with the noise levels of the signals you are trying to feed in.  Seems
to me like the success or failure of your project might lie in how good the
input amplifier circuit is.  The app. engineers at Teletone might be able to
help you out with this...
 
 
    Greg Bell_________________________________________________________
      Hardware hacker          |
      Electronics hobbyist     | UUCP:  uunet!serene!pnet12!gbell
      EE major at UC San Diego |