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'help for change PWM to DAC sin wave'
2000\01\22@021234 by gzkwan

 can anyone help me to do:
how change the PWM voice signal (Square Waves)  to DAC sin Waves??
I use the sunplus 6502 cpu to generation the DTMF voice signal,It can work
use the speaker close the telephone MIC  to send out the DTMF signal.
but I can not connect the DTMF SPK output pin to the phone line directness
I use the oscilloscope to watch the DTMF is a Squre Waves,
but another DTMF IC is the Sin Waves,So how can I exchange the PWM to Sin
Waves???calculus circuit is need??????? how can I do it????????

2000\01\22@040438 by Ken Webster

part 0 686 bytes
Here's the cheap way:

RC filter.  See attached schematic (.GIF).  Try R=10000 and C=0.1uF to start
with.  Increasing R or C will increase the time constant which will smooth
the output more and lower the lowpass cutoff frequency.  Decreasing R or C
will raise the cutoff frequency.  You may need to follow this circuit up
with a high-impedance amplifier (emitter follower or op-amp follower for

Note that this is not a perfect integrator -- it will introduce some
distortion.  If you need a better integrator just ask.  This should be good
enough for getting DTMF onto a phone line though.



Attachment converted: wonderland:pwmfilt.gif (GIFf/JVWR) (00015A18)

2000\01\22@070706 by gzkwan


Ken Webster wrote:

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