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Giordano 15th January 2008 10:49 PM

how to remote control a rotary switch based attenuator
2 Attachment(s)
Hi everybody,

I have a problem. I need to remote control the volume in a tube based system, but I'm quite struggling with it.

I have tried to make a binary controlled relay network, but it was not good enough. (

Now I want to go back to the basics and make a shunt attenuator on rotary switch. I was thinking about to make it with relays, but now I do not like relays at all and also I do not like the idea of the large pcb for at least 24 relays.

At the moment I use a black alps, which is turned by the smaller stepper motor (same type, from an old floppy drive) on the right side.

I have tried to make a control for the switch. First I have tried if the motor on the left side has enough torque or not, it has plenty. It turns it with half current.

Than I made a little program to step 8 step (about one position) and release. It does not work. The reason is, when I release the motor or turn the swith by hand it is left in an unknown step phase. When start to turn it starts sometimes backward and step a few in the right direction. This is because the motor is not in the position what the uC think.

Now I'm stuck here. I do not want any attenuator IC, not even relay, but stay with the rotary switch, but I have to solve the mechanical problem somehow. I'm looking for any suggestion.



Giordano 15th January 2008 10:51 PM

2 Attachment(s)
and these are the motor types I use.

The left one is really good, I can recommend it for potentiometers because it is 0,9degrees / step and the phase problem is hard to be recognized or rather not a problem at all.

jay1st 15th January 2008 11:03 PM

Why not use a small magnet or a light gate coupled to the rotary switch do detect the positions ?

ak_47_boy 15th January 2008 11:30 PM

You could use the actual switch to detect positions but a separate psu would be needed to avoid creating circuits in the signal path.

Giordano 16th January 2008 07:20 AM

of course it must get a separate PSU.

I had already some experiment with uC on tube elctronics. I have tried to shield it once, but I found the best solution is to send it to sleep when not needed. An interrupt from buttons or IR receiver wakes it up when needed, it takes less than a second to action it than it sleeps again.
Bottom line, when I listen to music, it is FULLY static. I do not use LCD display, or multiplexing of LEDs. As soon as it sleeps, there is no oscillator running, no signals changes going anywhere. If the PSU is not overloaded (would be hard to overload with a few LEDs and the few uA of the controller), this is not recognizeable in the sound. I know many tube funs will say proximity of a digital device disturbe the sound, but this is the way how to avoid.



Giordano 16th January 2008 07:30 AM

It is an option to know the home position, do not use the aretation of the switch at all, position with the stepper, but than I can not control it directly by hand.
Most likely this is the solution, I will build the wafers on the stepper, the small is enough than all I need is an accuratre home position detection.

If I can, I still want to rather add it as a feature, so I handle the rotary switch rod directly, but a motor can turn it also (when our 10month old baby got sleep in my arms, this all is for this mainly, I'm not that lazy :-)

... or, I just use a long rod from the armchair :-)



frigo394 31st January 2008 11:53 AM

This will solve your problem (i hope).
MV-01 complete volume remote control with ALPS motorized
pot ,for 35$ and 20$ shipping cost to Greece. (i think shipping
cost to Hugary will be the same )
MV-06 for 39.15$
Let me know if my reply helped you.

Giordano 31st January 2008 10:26 PM

Thanks, I have already a solution to control a black alps, but that is not strong enough for a rotary switch + there is a problem with positioning.

My problem is, my new amp (2A3 PSE) shows the quality of the black alps clearly, so I want to upgrade to resistor ladder on rotary switch. With a transistor based amp it helped to hide some sharpness.

(In the other hand, my dougter is 11month old now, she gets sleep other wasy more and more, not in my arms listening to Loreena McKennitt any more, so soon I will not need it much :-)



Jeb-D. 13th February 2008 08:06 PM

Make sure the motor steps are of angles equal to, or divisible by the rotary switches step angles. Example rotary switch steps are 15degrees. Then the stepper motors steps must be 15, 5, 1, ect. degree incraments.

Someone above also had a good point

You could use the actual switch to detect positions
Add an extra pole to the rotary switch and use it as a feedback mechanism. This approch would probably work good with a non-stepper motor as well.

Giordano 17th February 2008 10:44 PM

A found a thing I have never heard of : stepping solenoid. Looks like exactly what I want. The only problem is, they do not even respond to my emails. Two weeks ago I have called them and resend an email I sent before, but still nothing.

Have you heard of this ?



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