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Recently, I have experimented with an 8 Channel Light Joystick controller based on CDS (Cadmium-Sulfide) Photocells (available at Radio Shack : $ 3.00 U.S Dollars for five cells) .

In order to shield the 8 photocells from ambient light, they are all encased in a black plastic housing (such as the body of a 1/4" plug). These cells are then soldered to a PCB Board on a 45° angle (to shield the photocell from ambient light) and placed in a N-NE-E-SE-S-SW-W-NW configuration (see picture below). Each cell output should also be connected to a 100KOhm resistor to GROUND.

A tiny mirror is attached to the end tip of an homemade Joystick made out of a long screw drilled all the way through a small steel ball (such as the one used in a mouse or trackball) . This steel ball is then sandwiched between a curved plastic holder (mouse lock mechanism) and the patchboard itself.

When the joystick is tilted, the mirror reflects the light beam diagonally (at a 45° angle) to one of the cells: at that time the 100KOhm resistance ,present at the output of the cell, lowers to nearly zero Ohm and let a given amount of Audio signal or DC Voltage pass from the input to the output (it depends on the amount of light shining on the cells).

This 8 Channel Light joystick, which acts as 8 separate virtual potemtiometers, can control various devices from one single axis (VCO frequency-VCF cutoff point -VCA gain, Panning, Cross-Fading...whatever you want.....

Note: No power supply is needed, except a battery to power up a tiny lamp or white LED placed in the middle of the setup and shining upwards. . A 'one shot 'switch should be placed between the battery and the lamp. Under normal operation this switch should be depressed (ON) when the joystick is in use. When not in use, the switch should be in the OFF position (in order not to overheat the setup).

As an alternative to the above joystick/mirror configuration you can use a flashlight ,with an intensity level, to beam light directly into the individual cells.

Warning: avoid touching the Cadmium/Sulfide Photocells with your bare fingers : Yes, Cadmium (Cd=Atomic number 48, density 6.8) is a little bit radioactive :-(

(Extract of the Course 'The Art of Analog Modular Synthesis by Voltage Control - Chapter 10)

Copyright 1997 André C. STORDEUR - All Rights Reserved