>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

The answer is do not use a contact slider. Microchip have a capacitive 
sensor where one of the demonstration sensors is a slider. IIRC they have 
one that uses 4 capacitive sensors to get a 256 position slider. When I saw 
the development kit I figured it was an ideal way to make an IP67 slider ... 

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