I couldn't resist the urge to put cool lights on this project. For each finger I wanted a row of LEDs to indicate the X position and another for the Y position. The Z value is indicated by the brightness of the LEDs lit up in the X and Y coloumns.

The LM3914 is a ten LED dot display chip. It indicates an analog voltage level by illuminating one of the ten LEDs connected to it. I didn't want to use ten LM3914s to display the ten values, so I came up with a 5x20 LED multiplexing matrix design using 74HC4051s (analog multiplexers).

Only one of the five LED columns is illuminated at a time but they're cycled through fast enough to look like they're all on at once to human eyes. The signal to decide which column is illuminated come from three of the binary outputs on the vertical binary counter on the VGA board.

The top ten rows show a dot to indicate X position, and the bottom ten rows show a dot to indicate X position. Analog Multiplexers select different X,Y values to send to the LED dot chips depending on the column being illuminated.

I wasn't very happy with how this PCB turned out. I wanted it to be the same dimensions as the previous three boards, but there was too much stuff to fit cleanly. I had to use diagonal traces and too many jumper wires.

The display board stacked on top of the VGA signal generator, light detectors, and sample-and-hold boards.