Terry Smythe wrote in 040116 MMDigest:

> One such method is the non-destructive insertion of a set of
> electronic relays that can be individually actuated under the control
> of MIDI commands from a nearby computer.  Effectively, these relays
> do nothing more profound than substitute for holes in a roll.  The
> tracker bar need not be removed, just covered with blank paper with
> a tempo of zero.

Or cover the tracker bar with a piece of library-quality mending tape.
You may be interested in my article in Carousel Organ Association
Journal (Jan. 2004) on fitting MIDI control to roll-operated crank
organs.  Although much of my article is fine detail on building a MIDI
system into a particular common model of organ, I have plenty of
discussion and general ideas.

I use direct-electric pipe organ valves, from Peterson or OSI, which
are larger than needed and cost about $5 apiece -- no telling what more
would be charged to get them across Lake Erie and over to Winnipeg.
(Where is all this NAFTA agreement when ordinary individuals want to
exchange stuff between Canada and the US?).

There are, as you mention, web sites showing how to make electric
valves from small relays.  If you can get enough relays cheap (as in
surplus or scrap), and have the time to adapt them, that's a good route
to follow.

I've been working on an easy to make, cheap design of my own, using
commonly available materials, though you have to wind your own coils.
More on this later, if desired.

Mike Knudsen