MIDI Keyboard Encoder Wiring
The switches are organized in a 16 x 8 matrix arrangement. The switch keys
are wired as shown in the Keyboard Wiring diagram.
Note that the red dotted lines implies the extra
switches and diodes. For example, at the top, switches and diodes 0, 6 and 7 are
shown but the circuit is also wired similarly to switches and diodes 1,2,3,4 and
5. Also the other sides of these switches/diodes are connected down to RB1,2,3,4
So, for example, screw terminal connected to RD0 (via resistor R8) is wired
to one side of the 8 key switches SW. 0 to 7 and the wire can be looped from one
key switch to the next.
Each of the other side of these switches SW. 0 to 7 is wired to a diode on
the Cathode (K) side (end of diode with stripe).
The other side of each of these diodes is looped to 16 other diodes. For
example Anode (A) of diode DO is looped to D8 then to D16 then to D24 etc. down
to D120 and finally to screw terminal RB0 ( via onboard resistor R31).
The rest of the wiring is done in a similar manner.
Note that 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. However only the required switches and associated diodes
need to be wired.
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.