dr@ski.UUCP (David Robins) (09/11/87)
I am designing a DTMF link using IR as the transmission medium.
Using an AMI 2579 to generate the DTMF tones, its output can be
transmitted by either:
1)sending and receiving as analog sinewaves
2)modulating onto a 35kHz. carrier, and receiving as a logic-level
signal.
I have seen circuits done both ways, the most common being the analog
way, using an IR phototransistor as the receiver.
The digital way modulates a 555 running at 35 kHz, using a uPC1373
IR remotes-control preamplifier at demodulate and put out a
logic-level signal. (I like to concept of this device, because it
conditions the photodiode signal and adjusts bias to the lighting, and
has AGC.)
What kind of signal is necessary for the DTMF decoder (such as an SSI
202 from Radio Shack, or the Teltone M-957? Must they see an analog
sine-wave DTMF, or will a digital signal work. In fact, will the
uPC1373 preamp be able to deliver a signal that looks like DTMF still,
or will the pulses become sort of "width-modulated" and not work?
This digital problem would also occur if the analog system used too
much gain, and severely clipped the signals.
Any help appreciated- please email, as our news is removed in 3 days
due to disk space, and I don't check that often.
--
====================================================================
David Robins, M.D.
Smith-Kettlewell Eye Research Foundation
(previously known as: Smith-Kettlewell Institute of Visual Sciences)
2232 Webster St; San Francisco CA 94115
415/561-1705 (voice)
{ihnp4,qantel,dual}!ptsfa!ski!dr
The opinions expressed herein do not reflect the opinion of the Institute!