Remote Control of an Old Synth

On a sunny day (Tue, 15 Sep 2009 13:42:14 -0700 (PDT)) it happened Barry wrote in :

That is the nices picture of pot I have seen.

RC servos, PIC micro controller, RS232, this project of mine can control 4. The soft and hardware can easily be extended to control more. Noisy though, the servos make noise when turning.

Forgot the link:

If you don't mind tearing apart the synth, use motor-driven pots (search for them in the Mouser catalog).

If you do -- well, your life just got a lot harder. A bunch of RC servos, as suggested, with range extended to 270 degrees (which will be a challenge, since their internal feedback pots have the same range). A robot (tee hee!). I dunno if there's a realistic way to do it at all.

--
www.wescottdesign.com

There are some 360 deg servos, also winch servos that do a few turns.

On a sunny day (Tue, 15 Sep 2009 16:29:09 -0500) it happened Tim Wescott wrote in : . A bunch of RC

Gear?

In the theory, you can use some kind of servos to control the pots. Or replace the analog pots by digital controls. In practice, this is going to take a lot of work and it will be expensive, too.

If you are such skillful master of computing and analog grounding, why do you need the synth at all ? Generate the sound by software on your computer.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

Why not just replace them with digital pots? Or, as Vladimir suggested, just synthesize the sounds on your computer?

Have Fun! Rich

have You see

only for the curiosity sake! surely is not the device You want control... also I don't know the way to control the pots knobs by sw, but btw those arent variables somewhere in the memory? ( it talks about midi control too...)

bye delo

Why do you think so many of us are still using analog guitar pedals? ;)

Anyway, thanks for all your replies!

It seems I have three options.

1) Remove each Pot and use a motorized pot 2) Remove each pot and use a digital pot

Have any of you guys experience of using these alternatives in musical applications? How noisy is the motorized pot in terms of the amount of sound it generates as it rotates (as apposed to the sound might introduce into the circuit itself)? And how noisy is it in comparison to a normal pot with regard to the amount of noise it might introduce into the circuit? Likewise for the digital pot, is it less or more likely to introduce noise into the curcuit than the motorized pot? I'm thinking it will introduce step like changes in the resistence. What are the pros and cons between the motorized and digital pot in other words? Are there motorized pots that have "silent" motors that don't sound so much?

3) Use a servo.

I like this idea the most, but I'm guessing thats because I'm ignorant to the problems involved. Has anyone a picture of a servo controlling a pot? I've searched and searched but find it very hard to find what I'm looking for. I'd really be interested in any articles you can direct me to on this subject. I actually taught that there would be more examples on the net of people trying to control old devies from a computer. What servos are you using Jan? Again, are there "silent" servos?

Thanks again,

Barry.

On a sunny day (Wed, 16 Sep 2009 04:07:55 -0700 (PDT)) it happened Barry wrote in :

I am using standard Carson type RC servos: ftp://panteltje.com/pub/spare_servo_img_1559.jpg Those come in many sizes and forces,

There are a zillion ways you can couple a servo to a pot, here some simple ones that come to mind: ftp://panteltje.com/pub/servo_to_pot_img_1562.jpg In the left, this servo, a 180 degrees range one, is connected with a belt to the pot, the diameter ratio of of the disks is 270 / 180 to get 270 degrees on the pot. In configuration 2 the servos are opposite the post, and need to be able to do

270 degrees.

It all depends on how good you are mechanical, and in electronics. Modifying the electronics creates a solution that is less noisy. But can be very difficult as there exists dual gang pots, and log pots, and pots of all sorts with taps, and all sort of voltages may be present, and all sort of exotic resistance values maybe be used.

The idea of using LDR (light dependent resistors) with a light bulb controlled by a DA converter from the PC could work in *some* cases... gives good isolation, bad reproducibility, Re-designing that original electronics with the pots in it, is likely not for the faint of heart

There are very cool PC software solutions for musicians these days, maybe you can do everything on the PC.

You probably want quiet servos, but I don't know of any really quiet ones.

Here are some that may work. I'd buy one of each and try them out.

You may not be able to get a full swing of the pot out of a servo.

If you are worried about noise, put the servos in a box, and use rc pushrod cables to turn the pot. It'll look strange, but it may work.

Regards, Bob Monsen