[sdiy] DIY slide-bars

[Grant Richter]

Scotch No. 13 Semi Conducting Electrical Tape. Mouser has it. I just
measured it at 5K per inch.

The make the tape for over wrapping high voltage splices to drain away
electrostatic charges.

It is soft material though.

> From: Gene Stopp <gene at ixiacom.com>
> Date: Tue, 27 Jul 2004 17:24:27 -0700
> To: synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] DIY slide-bars
> 
> I've done two experiments with two different types of material.
> 
> First experiment: black antistatic bag material (opaque and rubbery), cut
> into a strip. Second experiment: conductive rubber cord (maybe 1/8" dia.)
> used for EMI gaskets. Both of these materials had a fairly high resistance
> per distance (several K per inch). What this caused is non-linear behavior
> and moving voltage points (i.e. yesterday 2 volts may be right *here*, and
> today it's over *here*, a couple inches away). Something like the Moog
> controller is more stable and repeatable, meaning you could mark the
> fingerboard with the voltages and they'll always be at the same places. I
> think it's because the resistive element was a pretty low resistance, driven
> by higher current. This would imply some kind of heating element wire, like
> in an electric heater. It may be only a couple of ohms so something like a
> power regulator might be needed, perhaps configured in constant current
> mode.
> 
> I've not run across such an element yet but I do have a note to self to be
> on the lookout for the next trashed bathroom heater or hairdryer.
> 
> - Gene
> 
> 
> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Rainer Buchty
> Sent: Tuesday, July 27, 2004 6:57 AM
> To: Magnus Danielson
> Cc: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] DIY slide-bars
> 
> 
>> 1) How did these classic slide bars work? What materials etc. was there?
> 
> In the Elektor magazine they just used graphite, i.e. you literally drew
> the slide bar, but then had a metal probe for sliding so your finger
> stayed clean :)
> 
>> 2) How could one make one today? I am looking for a fairly stable design,
> so
>> antistatic foam is out, OK?
> 
> I wonder if recording tape could be used in a setup like this:
> 
> ========    cover foil
> --------    recording tape
> ________    copper or some other conductor
> 
> The copper is attached to some sensible voltage. The recording tape
> basically acts as a trimmer, so that touching -- thus closing the
> contact -- is equivalent to the wiper. Now you take the difference (or
> better: the ratio) between the voltages measured at the ends of the tape
> and get the tap position. Could probably be further refined if the tape
> is crescendo-shaped.
> 
> (I'm quite sure people on this list have done something like this before
> and can tell me why that's a bad idea.)
> 
> Rainer