In the interest of safety (and energy savings) I have designed a little
circuit to turn on a MIDI-controlled instrument, for a fixed period of
time, upon detection of a signal on the MIDI line.  After the fixed
period, the device turns off.  Any MIDI activity during the 'on' period
will delay the turn-off by that same amount of time.  In other words it
is retriggerable.

The device is optically isolated and can cause no damage to the
controller or to the MIDI device.  It can be operated on the tiniest of
power supplies so that there is minimal electrical consumption when the
device is waiting for a signal.  Included is a bridge rectifier and
voltage regulator so it can operate on a wide range of AC or DC
supplies.

I have installed one on my MIDI-controlled Duo-Art piano so that I do
not have to worry about the pump running unnecessarily and risking a
fire.  The circuit outputs five volts to control a solid state relay
that handles the load.  Any AC or DC load can be controlled this way
by using the appropriate relay.

If there is interest, I can have a number of boards made and will sell
them for $20 each.  The components cost about $6.  I will also sell the
complete circuit, ready to use for $50.

Spencer Chase
http://www.SpencersErolls.com/