'help for change PWM to DAC sin wave'
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????????
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)
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