[sdiy] rotary switches in general

[Tim Parkhurst]

Build quality is going to be the biggest difference. The price may also be
set by how popular a switch is (more popular = higher production numbers =
lower unit cost).

One alternative that I've seen used by others is to take a pot, hook it up
as a voltage divider and run the voltage into a simple (2, 3 or 4 bit) A/D
converter. The output of the A/D can then control an analog
switch/multiplexer, transistors, or even relays. You'll need to add some
indicator LEDs to provide user feedback, but this is relatively easy. A very
simple "A/D" solution would be to use the LM3914 bar graph chip (10 outputs
= approx 3.5 bit resolution). This gives you the option of "bar" or "dot"
modes, and the outputs can be easily grouped together if you need fewer than
10 positions. Given the cost of quality rotary switches, the A/D setup
should be cost competitive, plus you now have a voltage controlled switch!

Here are some relevant URLs:

LM3914 data sheet
http://www.national.com/pf/LM/LM3914.html

I first saw the concept used here:
http://www.musicsynthesizer.com/Circuitry/sequencers_page.htm

There are some other examples of how to run +/-10V signal through a 4051,
but I can't find them right now. It can be done however, and I'll dig them
up if you really need it.


Cheers!

Tim (less popular/higher cost) Servo

"Imagination is more important than knowledge." - Albert Einstein




> -----Original Message-----
> From: mark s [mailto:djarum11 at mindspring.com]
> Sent: Monday, August 09, 2004 11:53 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] rotary switches in general
> 
> 
> would someone care to elaborate on the differences between a $1.50 rotary
> switch and a $10-$20 one? (USD)  is this a 'hearable' difference or a
> mechanical one or both ??
> 
> mark scetta
> 
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