MIDI Keyboard Encoder 

The keyboard encoder is capable of encoding any number of momentary action, push to make, single pole single throw (SPST), switches from 0 up to 127 to produce the equivalent MIDI note-on/note-off data commands. The encoded switches are wired via IN4148 diodes, see schematic circuit diagram. Also there is a wiring explanation and wiring diagram available.

This unit can be connected to new keyboards or it can be used with an older non-MIDI keyboard by using magnetic/reed switches to isolate the old and new scanning circuits. This will allow the older keyboard synthesizer to continue to operate as normal while also providing a MIDI output.

• The transmit MIDI channel (1-16) can be selected by a 4-way DIP switch. 
• The velocity byte is preset to the maximum value.
•  The keyboard encoder is 32-note polyphonic.
• The switches, 0 to 127, are defined in the MIDI Note Number to Frequency Conversion Chart.
  

The Keyboard Encoder to MIDI Unit consists of:

• A Printed Circuit Board (PCB), 
• A pre-programmed 16F877 PIC,
• The 4-way DIP switch which selects the MIDI transmit channel via DIP switches 1-4 (See Table 2) 
• The on/off switch and associated power-on LED,
• A 9 volt battery connector
• A MIDI 5-pin DIN output socket, see Circuit Diagram
• A screw terminal connector for an external 9-12 volts DC supply
• Three 8-way screw terminal connectors for connecting the external switches, see layout diagram

The Keyboard Encoder to MIDI unit requires:

• a 9v battery or equivalent DC power source
• Suitable key-switches and associated IN4148 diodes