Jim,
I have a similar project that I have been working with off and on for some
time now. It is a Balanced to Balanced Antenna Tuner feeding a loop antenna
with open wire, with coax to the station antenna switch. The tuner is
currently deployed in the attic, and is attached to the house LAN with its
own IP Address and port. The Stepper Controller I use is capable of
controlling two motors, and has been provisioned with a granularity of 1600
steps per 1 full revolution. And as with Stepper Controllers, you need to
talk to them via RS-232 or Ethernet or some other means in order to operate
the motors. One gentleman mentioned using a PIC processor as persistent
memory which could store the location of the motor during powered down
periods. That would definitely work, and I too have thought about that
method. I also played around with the idea of using precision resistors
geared up to the motor shafts using 5Vdc, feeding the subsequent voltage to
10 bit A/D converters. That method will work as well. But if wanting to
use the KISS method, and since you have to talk to the controller anyways,
why not write a simple GUI interface to control the motors as well as store
their location and the controller configuration data. That is where my
project sets right now; learning curve in using VB 2008 Express. So while I
still struggle with writing the GUI software, I am still able to talk to the
controller via command line. Now before placing the tuner in the attic I
did run some tests to determine upper and lower bounds for both the
inductors and the capacitor in terms of steps. And the motors are powerful
enough not to skip, even at that granularity. So I am reasonably assured
that the step location for each motor as reported by the Stepper Controller
is accurate. So for the time being I manually control the stepper motors,
and write down the location of where the motors sit before turning the
system off. My Stepper Controller board has the ability to accept and act
upon the input from "hard limit" switches. I may still use that feature as a
fail safe.
73,
Mike
W5CUL
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of 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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