Newsgroups: comp.robotics
Path: brunix!cat.cis.Brown.EDU!agate!library.ucla.edu!csulb.edu!csus.edu!netcom.com!quartlow
From: quartlow@netcom.com (Len Turnbow)
Subject: Re: radio control of parts
Message-ID: <quartlowCsytC0.L6q@netcom.com>
Organization: NETCOM On-line (408 261-4700 guest)
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References: <66.895.1262.0N5C5938@tabb.com>
Date: Fri, 15 Jul 1994 04:48:00 GMT
Lines: 52

Henry Liu (henry.liu@tabb.com) wrote:
(Snip)
: I'm looking to control parts via radio control (almost stangled myself with 
: wires <g>).  Anyways I thought about using Walkie talkies and an 
: encoder/decoder circuit (since I don't feel like putting one together 
: myself).  The only problem is how can I get analogue inputs into the 
: transmitter and get them back through the receiver?  Here is what I have 2 
: digital input (switches), and 2 analogue variables (potentiometers <sp?>). 

Your local hobby store has radio controls available for scale model use.  
The input at the transmitter end are just spring-loaded potentiometers.  
The output from a two-channel radio receiver is comprised of two separate
width-modulated pulse-trains, proportional in on-time duration to the
setting of the aformentioned potentiometers at the transmitter.  

Now, if you level-shifted the outputs of the receiver to TTL levels, you
could input them to a microcontroller.  Write the microcontroller
code to look at the pulse-widths.  If the pulse width is between, say
20% and 80% of range, output a proportional value to be converted to a 
voltage by a Digital to Analog Converter.  The voltage could then go to 
electrically adjustable potentiometers. 
Each of these E-pots output to your circuitry.

Still with me?

Digital Multiplexing, nifty trick:
Now, if the pulse-widths were between 5% and 15%, you could decode that as
switch ON.  Between 85% and 95%, OFF.  The other channel would contain the
other switching signals.  In this way, you could multiplex many digital 
signals through to a two-channel radio control.  If you had a repeatable
1% resolution in your code, you might be able to support 12 digital switches
in addition to two analog signals!  

Disadvantages:
  *  Your code would have to leave the E-pot settings as they were when
     a "switch" signal is being sensed.
  *  Don't expect lightning response.  The code necessary to filter
     noise on the pulsewidth information would probably tend to slow
     response time. 
  *  The "centering" adjusters on the transmitter would have to be 
     glued to prevent them from causing command misinterpretation.
  *  You would need to attach DPDT pushbuttons in series with the 
     transmitter potentiometer wipers at the transmitter end.  
     Voltage divider networks at that end would be switched in to
     emulate the pot at that position.
 
I would like to know how you did finally solve your R/C problem, even
if you didn't use this idea. (grin)

Good luck.

--Len  (quartlow@netcom.com)
