Hi Gerhard-

I think that if you consider the "envelope" of Pulse Position Encoding with each
of the channels being Pulse Width Modulation (one PWM per channel), then you
might have a clearer idea of what they are talking about.

With say, a six channel transmitter/receiver, the "frame" of pulse position has
six analog bits of information each one being a seperate PWM pulse.  This PWM is
then sent to the particular channel servo which translates the width of the pulse
to a position.

After sending all the channels, the "envelop" has a stop or end of frame to allow
for the receiver to resync.

Hope this helps!

 Cheers,

   Rich S.

---- Original Message ----
From:		Gerhard Fiedler
Date:		Mon 5/7/07 9:37
To:		piclist@mit.edu
Subject:	Re: [PIC] r/c receiver interfacing

Ariel Rocholl wrote:

> I agree the signal on the servo is PWM, but the FM transmitted is PPM
> coded - but this signal is not the one you care about when you use the
> one already decoded by the receiver.

I'm not sure I understand the distinction between PWM and PPM you guys are
making here.

AFAIK, PWM stands for "pulse width modulation" and this doesn't say what
type of information is encoded ("modulated") in the pulse width. See also
<http://en.wikipedia.org/wiki/Pulse-width_modulation>.

In that sense, any pulse signal of constant frequency that has the
information encoded in the pulse width is a PWM signal -- no matter whether
the encoded information is position, voltage, speed, motor current, etc.

Gerhard

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