The last version of the Z-volume mixer was integrated into the main XYZ control board and there was no way to adjust its behavior.

The new design is on a seperate board and uses a differential amplifiers to control a voltage-controlled-attenuators. The differential amplifier's amplification and common suppression are controlled by two separate potentiometers. A high level of differential amplification causes the attenuator to transition from fully closed to fully open between a few millimeters of finger movements. This produces tones that go off and on quickly ( a feature common to chiptunes). A low level of differential amplification means gradual increases in volume over several centemeters of finger movement. This is similar to the effect possible with theremins.

The suppression control potentiometer sets the distance at which the amplification begins. The fingers can start making sound a millimeter from the screen or several centimeters back. This means the instrument can be played by tapping fingers against the screen, wiggling them near it, or a combination of both.

A dual potentiometer is used to control the amplification. A change to a differential amplifier's amplification feedback resistor also produces a change to the common suppression. By using a dual potentiometer I can use one potentiometer to increase the amplification and the second to counter it's effect on suppression. This makes the control scheme simpler. I don't have to re-adjust the suppression every time I make a change to amplification.

Video showing the new Z volume mixer.

This is also the first video showing the new parts from other recent log entries: