🚀 go-pugleaf

In article <17966@cmcl2.NYU.EDU> hanley@nyu.arpa (John Hanley) writes:
#>      But since an X volt p-p square wave carries more
#>      power than an X volt p-p sine wave, you should get a better S/N ratio
#>      at the output using square simply because you applied more signal.
#>      Why doesn't this work?
#>

It does work, provided that the 3f, 5f, etc harmonics of the square-wave
don't cause you any problems.  The square wave has a fundamental frequency
content which is about 1.27 times the sine wave giving about 1.6 times the
power.  Of course the square wave has twice the power of the sine wave, but
the power in the harmonics doesn't help your S/N ratio.


#>
#>Addendum:  Bandpass active filter
#>
#>                                   R                 R
#>                           +----/\/\/\/-----+-----/\/\/\/-----+
#>                           |                |                 |
#>                         ----- C          ----- C           ----- C
#>                         -----            -----             -----
#>                           |                |                 |
#>                           +----------------+-----------------+
#>                           |                |    R/12         |
#>                  Rin      |   |\           +--/\/\/\/--GND   |
#>audio in  o-----/\/\/\/----+---| -\___________________________+------o Vout
#>                             +-| +/
#>                             | |/
#>                             |
#>                            GND
#>

Simpler circuit with roughly equivalent behavior and many fewer parts:

                   Rin
audio in  o-----/\/\/\/------+------o Vout
                             | 
                             |
                            GND


Unless you have a pile of op amps and R's and C's which are burning a hole in
your junk box (or other parts storage facility) and you are extremely
poverty stricken and take great delight in building and tuning multiple
bandpass filters, the integrated DTMF encoders/decoders are definitely the way
to go.

	pete peterson
	{decvax,linus,wjh12,mit-eddie,masscomp}!genrad!rep