Re: [amsat-bb] el cheapo rotor controller

[David Carr <dc@xxxxxxxxx>]

Greg,

The joysticks usually have pots of about 100K, so the full scale current 
is very small.  It seems to me that simple dual opamp in a buffer 
configuration with a 100K resistor on its output would solve this 
problem.  A small perfboard with the opamp could just be added to one 
end of the cable.  The joystick port supplies 5V and ground already. 

73,
David Carr
KD5QGR

Greg D. wrote:

> Hi David,
>
> This is an EXCELLENT idea.  I had no idea that the game port had 
> analog inputs.
>
> One question:  what is the input current that is needed for a full 
> scale reading?  The pots on typical antenna rotors are 500 ohm, which 
> I'm guessing is a little small (too much current) for a game port.
>
> Greg  KO6TH
>
>
> >From: David Carr <dc@dcarr.org>
> >To: amsat-bb <amsat-bb@AMSAT.Org>
> >Subject: [amsat-bb] el cheapo rotor controller
> >Date: Thu, 13 May 2004 01:23:47 -0500
> >
> >In the eyes of a college student everything should be cheaper... why
> >not rotor controllers?
> >
> >The PC gameport has four analog inputs [well sorta -- I'll explain
> >in a second] and four digital inputs.  It seems to me that the
> >ubitquitious and cheap nature of this port could be put to good use
> >controlling antenna rotors.  The "analog" inputs do not 
> work like a
> >conventional ADC, instead the port expects a variable current as the
> >input.  The port measures how long it takes for this current to
> >charge a capacitor to a known voltage and reports this time as an 8
> >bit value.  Most rotors that I've come across use a potentiometer
> >for position feedback and thus provide an excellent variable current
> >output.  Otherwise, if the position output is a true voltage source
> >a simple resistor in series between the voltage output and the
> >analog input should create the necessary variable current.  The
> >parallel/serial port could be used to output the appropriate motor
> >control signals.  Between these two ports and a simple relay board
> >we have a very low cost 4-axis rotor controller.  It seems to me
> >that this would go along very well with Bob's simple APRS tracking
> >system which I believe is open loop.  Even if your "legacy 
> free"
> >computer does not have a joystick port I'll bet you can pick one up
> >on a cheap sound card for <$10.  I'll have to see what kind of 
> code
> >I can churn up to make this work...
> >73s,
> >David Carr
> >KD5QGR
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