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> Did you know that there are people who are still making wax cylinders for
> Edison machines?

Yes, he has a reproduction plastic cylinder on the machine now with a
crystal stylus. Because this will be used so many times he's chosen to
remove the stylus and play WAV files. There are hundreds of cylinder
mp3 on the web, 100-odd of which we've sweeten up for tone and
edited for time. I put him on to

http://www.tinfoil.com/

and someone locally who was selling genuine antiques

> If I were you, I'd seriously consider non-contact solutions, such as
> capacitive sensing.

When Bob mentioned using a pulley and string like a radio the image that
popped into my head was "tuning" with the pointer and measuring the
frequency but that's way OTT

> For example, the brass crank could move a brass "pointer" along the
> surface of the PCB, almost but not quite touching it. Sensor pads built
> into the PCB artwork (sealed underneath the soldermask) would detect
> the presence of the pointer at particular locations

I've made capacitive proximity sensors like that (attached) but hadn't
thought about them in this application. The logic makes a 75kHz signal
that changes amplitude via a capacitive divider (made of the bridge
capacitances and the human body). It will detect a hand through several
centimetres of wood with a big enough pad, say 50mm x 100mm of
aluminium foil. The op-amp amplifies the amplitude change and an
integrator + Schmitt trigger removes the noise to produce a clean logic
output

I'd be interested to see any schematic you have of a simpler sensor, as
anything that has no touching parts would have a servicing advantage

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