Topsy 3


The organ is designed to play MIDI files arranged for a 64-note system.

The MIDI files were originally played using a Palm Vx handheld computer running a program called ittyMIDI.  The Palm Vx has a standard RS232C serial output.  This was connected to an adapter allowing it to control any MIDI instrument, including the MIDI decoder.

More recently, I have been using a Raspberry Pi computer,  running Linux,, and using a USB/MIDI interface

The organ is fitted with a MIDI decoder board purchased from  j-Omega Electronics.  This takes a standard MIDI signal and converts it to 64 separate on/off signals capable of operating the solenoids.


In order to allow the MIDI file to control which ranks of pipes are used and additional control board will be needed.  This will intercept some of the outputs from the MIDI decoder and use them to operate the controls for the celeste, octave and glockenspiel.

John Smith has provided the basic circuit diagram and I have designed my own circuit board from this but have yet to build it.

Speed Control

The bellows can be cranked by hand but I have also included a motor option.  As the reservoir fills and empties, it operates a couple of microswitches to signal when it it nearly full or empty.  These are connected to a small circuit board that runs the motor as three adjustable speeds.

John Smith provided the circuit diagram for a suitable speed control but gave no details of the physical layout of the board.  I worked out my own layout using stripboard and it is working successfully.  I still need to adjust the values of a couple of resistors as my motor  runs rather fast at the moment.  However, I will wait until the organ is complete as I have only tested it with twelve pipes in so far.