> From:         Robert B.[SMTP:piclist@NERDULATOR.NET]
> Sent:         Thursday, June 24, 2004 2:48 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [EE:] Analog signaling

> I recently had an idea (probably ages old) for the transmission of data on a
> continual basis using analog voltages, and would like to get some criticisms
> on it before I get too deep into trying to make it work.  The basic idea is
> to use frequency-dependent filters to determine the amplitude of some analog
> signal at a given frequency.  Perhaps the best way to explain the idea is
> with an example:

> Example:  Take a robot with 40 separate actuator "muscles".  For now just
> consider the actuation control and disregard the feedback mechanisms. To
> establish real-time control of 40 actuators on a digital link would not be
> impossible, but would perhaps restrict expandability, etc.  So we assign
> each "muscle" a control frequency based around a signal amplitude.  Muscle 1
> gets 20khz, 10vpp centered on 0v.  To move it from neutral, the amplitude of
> the 20khz signal drops to say 5vpp or rises to 15vpp.  The actuators are
> tuned to listen on a specific frequency, which is then smoothed to a
> relatively DC voltage.  All 40 actuators are installed as said, at perhaps
> 22khz, 24khz, ... and so on (no calcs yet, but assume there is enough
> bandwidth), each with an independent filter to see what component of its
> tuned control frequency is present.  So now to control all 40 actuators at
> once it would (only?) be necessary to sum 40 separate control signals into
> one analog signal, and inject that to the backbone where each actuator will
> single out its respective command.

> The apparent advantage of this method (to me) would be the increased amount
> of data transfer on a single wire, with the primary disadvantage being
> somewhat imprecise control all around.

> . . . .

Something like this was proposed in the early days of the telegraph as a way
to send multiple signals on a single wire. It was called the "harmonic telegraph"
but I can't remember the inventor (Morse?, Bell?, someone in Europe?).

In the very early days of radio controlled models (the vaccum tube days),
something similar was used for multi-channel control. The audio output from
the receiver was sent to an electromagnet mounted under a metal comb
formed from spring steel. The teeth decreased in length across the comb,
much like the "harp" found in music boxes. Each reed had a different
resonant frequency; on the end of each was a contact which would touch
a fixed contact below it. The vibratory signal from each contact was filtered
and discriminated to make an on-off signal for each reed.

John Power

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads