Keyboard Interface

The first chapter of the book MSS 2000 deals with the keyboard interface, but I did not like the concept of desoldering all diodes from the keyboard contact boards and connecting the rubber contacts to external boards filled with electronic switches, so I decided to use the keyboard as it is and developed a controller to be directly connected to the keyboard interface connectors.

As my synthesizer would not be a stage instrument, I did not think about analyzing key velocity nor usage of wheels, but it should be polyphon.

The first problem I had was the electronical check of the rubber key contacts. It was quite easy to identify the pins of the keyboard interface connected to the diode matrix of the rubber contacts, but the resistor value of the rubber contacts was grater than 1 MegOhm even by usage of maximum finger pressure.

So I developed a fet opamp solution:

The output matrix of the 'keyboard guardiens' (I0 - I7) x (Q0 - Q7) which contains the coordinates of the pressed keys are multiplexed on the digital synthesizer bus where they are sniffed by 'their' (voice depending) DACs and where they are converted into a CV and a GATE signal. Schematic:

Update 11.01.2005: This keyboard interface is not in use anymore. Please see Simple MIDI Keyboard

Please send questions or remarks to:
Carsten Toensmann

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