Actually, Peter, I think microswitches would be pretty difficult to
implement, since vacuum variables are mult-turn devices. I know there were
commercial ETO MRI amplifiers that used vacuum variables, and their homing
mechanism used a stack of interlocking plates that were indexed so that
after ten rotations, a small detent on the top plate in the stack ran into a
stop and tripped a microswitch. The technique worked but was pretty complex.
Air variables are usually initialized by attaching a thin metal disk with a
slot or hole to the shaft, and using an LED and a photoransistor to detect
the closed capacitor.
73,
Jim W8ZR
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of peter
chadwick
> Sent: Sunday, April 27, 2014 2:46 AM
> To: ww1c@outlook.com; k7fm@teleport.com; amps@contesting.com
> Subject: Re: [Amps] Auto tune conversion using stepper motors?
>
> Being somewhat cynical, I would rather rely on a system with microswitches
to detect the
> end points rather than electronics - far less to go wrong. It's not
difficult to do.
>
> 73
>
> Peter G3RZP
>
>
>
> ========================================
> Message Received: Apr 27 2014, 09:10 AM
> From: "Markku Oksanen" <ww1c@outlook.com>
> To: "Colin Lamb" <k7fm@teleport.com>, "Amps" <amps@contesting.com>
> Cc:
> Subject: Re: [Amps] Auto tune conversion using stepper motors?
>
> Hi
> Thanks for the ideas.
>
> Does anybody have a good idea how to find the "zero point" on vacuum cap
without
> adding a potentiometer for position feedback? I was thinking about
reflective optical
> sensors and setting them up so that when the cap opens up totally, the gap
between the sides
> of the capacitor are detected as a drop of reflection . These sensors are
really inexpensive,
> only thing is how to position them correctly and accurately.
> Markku
>
>
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