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how to remote control a rotary switch based attenuator
how to remote control a rotary switch based attenuator
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Old 22nd February 2008, 08:07 PM   #31
Giordano is offline Giordano  Hungary
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Join Date: May 2005
Location: Hungary
dnsey, you touched a very important point, I forgot to mention. Even for the alps pot turning it is very important to keep the current switched on for a bit after turning. Even the 220mm long aluminium rod I use have that much flexibility (with the junctions) that you step 2-4, if you release the current immediately, the motor is turned back, because the pot is not turned yet !

An easy experiment shows it clearly. Years ago when I have tried my first program, for every IR receive it stepped 2. I have tried it on a bench, nothing was connected to the motor. When I pushed the button on the remote controller, the motor did crazy things sometime. Even making noise but rod not rotating. That was because after the step I released the current immediately. First I added a bit of delay and it solved the problem immediately. Crazy, but I have spent hours to find out what a hell is going on. I did not tried the motor and the control IC before, I thought one is faulty or I did not wired it correctly.

So, coming back to your idea, it might help, but yet I found the more flexibility I have in the connection rod, the more difficult to tune the control. For the pot, I have tried to make it as solid as possible. For small steps, you need to wait more for the pot to follow it if the rod is more flexible.

Regards,

JG
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Old 27th February 2008, 08:04 AM   #32
gmphadte is offline gmphadte  India
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Join Date: Jul 2003
Location: Dona paula, Goa
I do not know whether this is feasible/cheap
If u can fix a position detector(?) or phase detector on the shaft of the stepper motor, then u can call this value to decide your next phase, if the shaft detent has shifted it.

Gajanan Phadte
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Old 1st March 2008, 07:10 AM   #33
Giordano is offline Giordano  Hungary
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Join Date: May 2005
Location: Hungary
gmphadte, to be honest I did not found a good angle sensor under 100EUR. the one I found is 230EUR and quite big.

Anyway now I'm quite confident it is not necessary. The fine motor will be enough (400 step). The error will be about 2.5 degrees only, worst case. I'm about to finish a dac now. In ~2 weeks I will get back to the vol control.

Regards,

JG
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Old 1st March 2008, 07:47 AM   #34
dnsey is offline dnsey  United Kingdom
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Join Date: Mar 2004
Location: Shropshire, England
You could easily make an optical position sensor yourself.
Prepare the artwork using drawing software, then print it onto clear acetate.
Once you have this fixed to the attenuator shaft, you don't need a stepper motor at all! Just use an ordinary geared motor, and let the position sensor control it directly.
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Old 1st March 2008, 09:56 PM   #35
Giordano is offline Giordano  Hungary
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Location: Hungary
see the beginning, you can not rotate the dc motor with the gears
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Old 2nd March 2008, 06:55 AM   #36
dnsey is offline dnsey  United Kingdom
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Add a magnetic clutch to decouple the motor when not in use.
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Old 2nd March 2008, 03:48 PM   #37
gootee is offline gootee  United States
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Join Date: Nov 2006
Location: Indiana
"Starting over, fresh", on this, in my mind, and thinking about it for just a few seconds: Just 'off the top of my head', I kind of like the idea of using a rotary switch and a stepper motor that both have the same number of steps per revolution. Solenoids also seem like they might be simple-enough. But, with a small-enough DC motor, probably with some sort of gearing reduction, with a small-enough clutch, it could VERY-easily be made to work, with position feedback available, if size could somehow not be a problem. If it weren't for the possible size problem, the last method seems easiest to implement, for me at least.
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Old 3rd March 2008, 03:26 AM   #38
gmphadte is offline gmphadte  India
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Join Date: Jul 2003
Location: Dona paula, Goa
Giordano wrote
Quote:
gmphadte, to be honest I did not found a good angle sensor under 100EUR. the one I found is 230EUR and quite big.
After I went home and was at a highly relaxing place(!), I got another idea.

Issue is to detect the motion without drive signal.

A slot sensor can be used along with a slotted wheel to detect uncontrolled motion. For manual rotation, u will have to use quadrature detector to subtract cw/ccw counts in case of manual turning.

Now this may not be of interest but is an easy and cheap solution.

Gajanan Phadte
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Old 7th October 2008, 11:29 AM   #39
milen007 is offline milen007  Indonesia
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Join Date: Dec 2007
hi guys

how it turn out? i am also struggling to get remote control for my rotary switch that i do not want to change to the switch.

i only need the mechanic part that can be control by remote.

thanks in adv
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Old 7th October 2008, 09:31 PM   #40
Giordano is offline Giordano  Hungary
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Join Date: May 2005
Location: Hungary
I am successfully using a bit larger stepper motor which has very small breaking force when de-energized (not sure my English is clear, with other words, very easy to rotate when not drived), so when I stop with the motor and de enrgize it, it jumps into the middle of the step. The starting problem/phase problem is still here, it stats sometime a wrong direction with 1 step. This motor I found (old 5.25" floppy head motor) is a 400 step motor, so with half step it takes
22 half steps (as I remember) for a step at the switch. 4 half step in the wrong direction worst case is 1.8 degrees.
Not perfect, needs matching of the switch and the motor, but works and there is no additional gears, cluthes etc. That would probably be better, but I'm not good in mechanics.

Regards,

JG
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