This video shows two units being used to add eight Werkstatts to a Moog Grandmother.

Midi Quad Uno (zip)

These are the sources that currently control the Arduino UNO version of the quad unit. The source defines the pin mappings using defines so that you can wire the Arduino up in a different order. The only special purpose pins that are being used are the TX and RX (D1 and D0) for MIDI in and out. Two of the outputs are used to clock the Werkstatt keyboard logic (CLK) and reset the keyboard counter ( MR). Groups of three pins are used to control each Werkstatt. The LOW and HIGH pins are used to control the +16 semitone and +32 semitone control voltages. The third pin is used to read and write the multiplexor common pin which allows the D/A latch to remember the counter value and drive the gate logic.

CLKCommon clock output signal to drive the counter on the Werkstatt
MUXPer Werkstatt in / out, the common of the switch matrix multiplexer. Used to drive the gate and counter latch. Can also be read to see if a key is pressed.
MRCommon counter reset output signal.
LOWPer Werkstatt output, enables the +16 semitone analog signal.
HIGHPer Werkstatt output, enables the +32 semitone analog signal.
GNDCommon GND ( 0v ) signal.

To control four Moog Werkstatt and have MIDI In / Out, four signals are used to provide Midi RX and TX, CLK and MR. For each Werkstatt three signals are used to read the multiplexor (MUX) and generate the two extra bits of the note value to provide a total of 6 bits of digital data that is converted into a control voltage that is used to set the VCO frequency.