Greetings Bill, My name is Michael and I live in Kiama just south of
Woolongong.  If you have not already found it, Dave Kerr's home page in
Canberra may help you.  Dave has built a calliope with MIDI control and
there is a good description with pictures:
http://members.iinet.net.au/~mydav/

I'm building a fairground organ with MIDI and as a pensioner I have to
watch the budget, so I built some extra circuits on a old Commodore 64
computer, using tri-state latches, TTL 5-volt logic and with a MIDI
input I added, and some programming using an assembly program (BASIC
is not fast enough).

I decoded the MIDI info to 5-volt 'note on' and 'note off' with a span
of 96 notes.  Since I did this there is now a PC Board that does nearly
the same thing (see Dave Kerr's web site).  It's expensive to buy but
more compact; I might get one later.

To get the 5-volt output of the computer to run relays I use Darlington
driver ICs, ULN2803 from Dick Smith cat. no. z6282.  These have 8
drivers in one IC and can supply max 500 ma @ 50 volts.  They cost
about 5$ each.  My relays came to me from old telephone exchanges
through ham radio contacts.

I connected the double-wound relay coils at 500 ohms each in parallel
to get 250 ohms and used 35 volts dc supply.  35 volts / 250 ohms =
.140 amps or 140 ma.  They are already diode protected and so far have
performed well.

Hope this info is useful to you.  Email me if I can help you further.

Michael Taylor
m_taylor@dodo.com.au.geentroep [delete ".geentroep" to reply]