The MIDI CPU Project – 3. Bass Pedals

After building the MIDI CPU box and programming it to accept input from keys, switches and potentiometers, it was necessary to build MIDI instruments to use its features.

As the MIDI CPU accepted input via a 25-way DIN socket, it would just be necessary to equip each instrument with such a socket and link it to the MIDI CPU with a suitable cable.

The first instrument I’d planned was a set of 13-note bass pedals, and the initial SysEx file with which I’d programmed the MIDI CPU was suitable for this application, with the first 13 control terminals, 0 – 12, configured as a complete octave from C0 to C1.

I got the pedals from a local seller on eBay who dismantled and repaired Hammond organs.

They were in excellent condition, and the switches on each of the pedals seemed to be still wired.  They looked like this:

and the actual connections were like this:

The two tabs on the front linked one side of all the switches together; when a pedal was pressed, this bus would be connected to the other side of that individual switch, the tab on the top.  This was perfect for this application, in which an individual switch connected to 0v would be interpreted by the MIDI CPU as a note command.

My main task, then, was to connect each of the 13 switches to a 25-way socket, in order to pass the switch presses to the MIDI CPU box.

In addition to this, I wanted to have Octave Up and Down and Hold commands available, so there would be 3 further connections to the 25-way socket.

Finally, I would have to construct a housing in which the pedal unit would sit.

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There were no circuits as such involved in this project – it was just a case of wiring up the switches and connecting them to the socket.  At the same time I decided to add a couple of extra sockets that would enable the pedals to be used in a different way if necessary.

The additional sockets added were a 15-way socket, which would be compatible with the Superstylonanophone (another MIDI device, with  a built-in MIDI-USB interface):

and a 9-way socket compatible with the Apple IR remote:

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I connected the switches to the sockets and, because the enclosure I had planned was designed to have another instrument on top of it (another MIDI foot controller, a Digikick Footar) I connected the Hold and Octave Up and Down connections to 1/4″ sockets so these switches could be external, rather than on the top of the pedals.  All the sockets were housed in a small panel, which would be attached to the rear of the enclosure.

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After connecting the switches to the sockets, I found a D25 cable and attached the Bass pedal unit to the MIDI CPU box.  At the moment the MIDI CPU box is connected to a laptop via a Midisport 2×2 MIDI-USB interface – along with the Digikick Footar – and controls software instruments in Apple Logic.

I added 2 or 3 different bass instruments to the Logic set-up and tested the pedals.  All notes worked as they should.

With an external switch I tested the ‘HOLD’, ‘OCTAVE UP’ and ‘OCTAVE DOWN’ functions, which seemed to be working OK, so deemed it safe to screw down the top of the case in which the pedals were housed and fix the panel to the back of the case.