I would like to thank all respondents for their invaluable advice on
the subject of vacuum sensing.

Perhaps I should outline my objectives more clearly: I am neither
trying to re-invent the wheel here nor do anything too costly or
complicated -- I am simply experimenting.  I would like to find a
modern, efficient solution to satisfy the demands of my customers in
order to make player pianos as attractive (and reliable) as possible,
but without spending a fortune.

I have occasional requests from clients to electrify players, especially
ones that I have restored.  Personally, I prefer to pump players, but
business is business and the customer is always right.  

My experience so far of putting an electric pump into a fully airtight
system, especially on a modest standard player without expression
features, is that it runs the risk of thrashing the instrument.  I wince
when I hear my lovingly reconditioned piano action banging around at
FFFF volume.  The motors that I have used so far seem to be too
powerful at the low end of the scale.

So I am looking for better methods of control, taking into account all
factors:-

1. Ease of supply of parts: preferably UK-made motors and controllers;
2. Cost: less than $500 for all components;
3. Total dynamic flexibility in terms of motor speed, from 0 to 100%;
4. Choice of preset suction levels to suit a particular instruments needs;
5. Switching to a definable suction level for rewind;
6. Automatic cut-off at end of roll;
7. Feedback of suction levels.

Achieving all of these may prove impossible, but that is where I am
starting from.  I will keep the group informed.

Roger Waring - The Pianola Workshop
Solihull, United Kingdom
http://www.pianola.co.uk/