Quoting ivp <joecolquitt@clear.net.nz>:

> Hi all,
> 
> I've got a project which involves selecting from a menu with a long
> slide switch. It will be made of a piece of PCB about 200mm long
> with 20 tracks going off to a PIC ADC. The user control is a slider,
> which moves a finger to complete the circuit. The idea is that the
> position of the circuit completion means a distinct voltage at the ADC,
> like a 1-way 20-pole rotary switch rolled out
> 
> 20 positions is a separation of 50 in the ADC. If that turns out to be
> too fine then the 20 can be split into 4 groups of 5, using 4 ADC. The
> PIC has nothing else to do except pass this information on so pins use
> is not a problem
> 
> My concern is what material to use for the tracks. As this is a one-off,
> and I haven't found out what expense is involved, I don't know whether
> gold flashing or carbon would be an option. And might not be hard enough.
> Bare copper is probably out, so too perhaps tinned tracks. I can imagine
> poor contact and noise after a time
> 
> I've got some thin tin plate, as used for screening boxes, which might
> do. Had it for a while and it still looks bright enough but don't know if
> it would corrode if abraded by a moving contact. Maybe some brass
> shim, but that gets a patina pretty readily
> 
> Any suggestions or experiences ?

Why not a slide potentiometer?  If you need indents, then perhaps you could add
them.  Likely to hold up better and easy to obtain, eg
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PP1045SD-ND

David


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