Basic Hardware Description

The initial circuitry is identical for pitch and volume.  A moving hand 
near each antenna affects the frequency at which the Schimitt-Trigger 
4093's oscillate.  The XOR gate takes the beat frequency of the antenna 
and variable reference frequencies. The circuit essentially produces 
two DC levels which are converted into digital form and read by the Z-80.  
The two ADC's give the Z80 a pitch byte and a volume byte.  After the 
Z80, these bytes are converted back to their analog equivalent and 
used to control a VCO and VCA.  

The four converters are wired in this manner:

A7  A6  A5  A4  A3  A2  A1  A0    Port    Device
       
1   1   1   1   1   1   1   0     FE      Pitch ADC

1   1   1   1   1   1   0   1     FD      Volume ADC

1   1   1   1   1   0   1   1     FB      Pitch DAC

1   1   1   1   0   1   1   1     F7      Pitch DAC