Speaking in broad generalities, that's all you need to do. PIC processors, as
an example, have flash memory that can be used for persistent storage. You
turn your relative position indicator into absolute by a calibration routine
that measures the number of steps from min to max. Set a counter to zero at
min and increment it as steps are executed. When he counter reaches the max
number of steps, you are at the max limit. When it's zero, you are at min. As
long as you store the counter value in persistent memory and there is no way to
move the control when the controller is powered off (without recalibration),
you always know where you are.
Al
AB2ZY
________________________________________
From: Jim Barber [audioguy@q.com]
Sent: Monday, August 08, 2011 5:01 PM
To: Al Kozakiewicz
Cc: Jeff Blaine; Amps@contesting.com
Subject: Re: [Amps] "Best" limit indicators for multi-turn, shaft-driven
gadgetry
No argument here, but you still have to have zero and full-range limit
indicators, or "stops". A shaft encoder (or just counting motor steps,
which is what I would probably do) gives you relative position, but
generally not absolute.
Unless, of course, someone begets a better mousetrap - which is why I
posted the question here. :-)
Thanks,
--jim
Jim Barber, N7CXI
On 8/8/2011 1:57 PM, Al Kozakiewicz wrote:
> I'm a digital kind of guy. I think the combination of an optical shaft
> encoder and a microcontroller (PIC, Arduino, whatever) to handle the various
> control tasks would give you a lot of flexibility without resorting to a lot
> of the control implementation in hardware.
>
> Al
> AB2ZY
> ________________________________________
> From: amps-bounces@contesting.com [amps-bounces@contesting.com] On Behalf Of
> Jeff Blaine [keepwalking188@yahoo.com]
> Sent: Monday, August 08, 2011 4:22 PM
> To: audioguy@q.com; Amps@contesting.com
> Subject: Re: [Amps] "Best" limit indicators for multi-turn, shaft-driven
> gadgetry
>
> Jim,
>
> I don't have an answer for your actual question. But the pot idea is good
> for another reason. In that would open the door to an
> auto-tune kind of option (or at least, the ability to record presets which
> via the ADC input, could be used to set the cap via the
> stepper). If your drive and antenna loads are stable, that would be very
> cool and not too complicated to code up.
>
> 73, Jeff ACØC
> www.ac0c.com
>
> -----Original Message-----
> From: Jim Barber
> Sent: Sunday, August 07, 2011 4:45 PM
> To: Amps@contesting.com
> Subject: [Amps] "Best" limit indicators for multi-turn, shaft-driven gadgetry
>
> I've reached the point where I need to decide whether or not to make my
> YC156 project amp "remote". Because of other interests, I already have a
> good selection of larger stepper motors and drive electronics, and a
> good feel for how to put it all together.
>
> What I don't have is a good, simple limit stop/reference concept for the
> vacuum caps and (possibly) roller inductor. I've used drive screws and
> leaf switches in the past, but don't like the mechanical sloppiness and
> complexity. I've also seen optical interruptors used in place of the
> leaf switches, but still don't like the mechanical complexity of the
> whole drive screw, platform and guide assembly.
>
> My favorite candidate at the moment is a high-quality 10-turn pot in the
> timing belt path for each shaft, "gearing it down" so that (for example)
> a vacuum cap that rotates 13 turns end-to-end would run 8 or 9 turns at
> the pot shaft. Using regulated 5VDC, I could then apply the output of
> the (pot) divider to a 10-bit ADC. Note I already have ten 10-bit ADC
> inputs at each control processor, so that isn't as much of a
> complication as it might seem.
>
> Any thoughts or suggestions?
>
> Thanks,
> Jim N7CXI
>
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