Hi John,
I've done some of that.
For roller coils and vacuum caps, I use 2K-10K ten turn pots (Bourns,
Helitrim, Spectrol) with 1/4" shafts.
You can just count the turns on a roller coil to judge the correct ratio. A
2.5 to 1 ratio will accomodate most vacuum caps.
I've used both 48 and 72 pitch, brass, aluminum and plastic gears. The
absoulute gear sizes are chosen to provide a typcial 1.5" clearance between the
shafts. Providing a small adjustment of the pot mount allows precise meshing
of the gears.
For readout, I use Microchip PIC's with a 10 bit A/D converter. Their A/D
includes a multiplexer to accomodate several pots. Ten bit resolution
conveniently covers a 0-999 digital readout range. No precison reference is
required as the potentiometer setting is just read as a ratio of the supply
voltage.
Three conductor shielded cable is used to connect the pot to the PIC and the
pot wiper lead is bypassed at both ends of the cable. The shield is only
connected to frame ground; No connection is made to the pot leads.
73 & Good morning,
Marv WC6W
http://wc6w.50webs.com/
--- On Wed, 2/25/09, John E <johne@tds.net> wrote:
> From: John E <johne@tds.net>
> Subject: [Amps] Digital read out
> To: amps@contesting.com
> Date: Wednesday, February 25, 2009, 6:02 PM
> Some time ago I came across a operator that was using
> Potentiometers
> with roller inductors and variable caps to indicate their
> position via a
> meter or digital read out.
>
> Have looked the web over and can not find this info.
>
> Any one know where it is ? or know what ohm and turns work
> out ? or
> gear ratio ?
>
>
> Thanks de John KØCQW
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