[sdiy] DIY slide-bars

[Brett, Bill]

Nichrome wire seems to be readily available over the web. Has anyone
tried this stuff?

-Bill
-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Gene Stopp
Sent: Tuesday, July 27, 2004 5:24 PM
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


-----------------------------------------
This message (including any attachments) may contain confidential
information intended for a specific individual and purpose. If you are not
the intended recipient, delete this message. If you are not the intended
recipient, disclosing, copying, distributing, or taking any action based on
this message is strictly prohibited.