[Amps] Auto tune conversion using stepper motors?

[Jim Garland]

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 at contesting.com] On Behalf Of peter
chadwick
> Sent: Sunday, April 27, 2014 2:46 AM
> To: ww1c at outlook.com; k7fm at teleport.com; amps at 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 at outlook.com>
>  To: "Colin Lamb" <k7fm at teleport.com>, "Amps" <amps at 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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