Trident, 3-Voice Light Theremin

This is an interesting combination of three light Theremin circuits which are each modulated by LFOs (Low-Frequency Oscillator) and have flashing LEDs that affect the accent of the other drones.

On each tower you can adjust the speed of the LFO, volume and pitch; and then play it by changing the amount of light falling on the sensors on the top and sides of the towers.

The circuit uses 3 pairs of oscillators made from feedback loops with the 6 inverters in a CD40106 chip. In each pair one oscillator is set to an audible pitch range while the other is set to a low frequency range and this slower oscillator is used to create a kind of hard-sync effect, providing some really interesting rhythms.

Each tower has 2 LDRs (Light-Dependent Resistor) - mounted on the top of the tower and on the front, just above a bright LED which flashes at the LFO speed. The front-mounted LDRs on the other 2 towers then pick up the light from these oscillators which modulates the pitch, creating a sort of portamento or slide effect.

You'll need to 3D print the files included, print times shown from my Ender 3 Pro at 28mm layer height (low quality):

• Towers (3-part layout) x3 ~= 2.5 hours per tower
• Base x1 ~= 4.5 hours
• Base Cover x1 ~= 1 hour

• Soldering Iron
• Amplifier or powered PC speakers

• Stereo Speaker Cable with 3.5mm Jacks
• 9v Battery / DC Power with 5.5mm Jack
• Optional torch

• Stripboard 14x15
• Various colours of wire (I use 30awg)

Capacitors:

• 100nF x3
• 1uF(e) x3

Resistors:

• 100Ω x3
• 1k x3

Potentiometers:

• B100k x4
• B10k x1
• B1M x1
• B10k (Linear Fader) x1

Semiconductors:

• LDR (~100k-500k) x6
• 1N4148 x3
• LED x3
• CD40106 x1

Hardware:

• DC Jack Socket x1
• Stereo Jack Socket (3 lugs) x1
• 5mm LED Plastic Bezel x9
• M2x5mm Screw x6
• M3x4mm Screw x3
• M3x6mm Screw x1
• M3x4mm Threaded Insert x3
• M3x6mm Threaded Insert x1

Print the sections; you'll need the base and cover as well as 3 towers. If you print the towers one-by-one, you can wire up each tower while you're waiting for the next one to print.

Each tower print is split up into 3 sections to make wiring and assembly easier. The cutaway at the bottom will allow you to slip the linear potentiometer in place and screw it to the longest face. See the wiring layout photo for how to connect the potentiometer, 2 LDRs and LED; make sure to feed the wires for the LDRs and LEDs through the holes in the printed case before you solder. Mount the LDRs and LED in plastic bezels and twist the 2 pairs of wires coming off the unit before threading them through the letterbox in the bottom section of the tower.

When you have the base printed, use a soldering iron to melt the threaded inserts into the cover screw mount positions and the PCB riser. Then mount the stereo socket and the power socket into their recesses in the base before mounting the potentiometers around each tower - you should mount a B100k next to each tower, along with 1 of the 3 LFO frequency pots: B10k, B100k & B1M. When everything is screwed in firmly, but before we tackle the circuit board, solder wires to the jacks and pots ready to connect up to the board when it goes in (make sure to have enough wire to reach the board, use 5" lengths if you're unsure).

Now build the circuit board. Cut the stripboard to size by scoring a line on both sides and then snapping; drill through the copper traces where shown on the diagram and drill a 3mm hole all the way through to mount to the base. Then solder all the components to the board - use a socket for the IC if you can.

Bring the circuit board to the base, but don't screw it in place yet and get the power socket, jack and pots soldered in place. Thread the wires from each tower up through the triangular holes in the base and solder them to the board. Now you can screw down the cover, plug in 9v DC power from a battery or a wall-wart and plug the output into an amp or powered PC speakers.

Have fun making some really weird noises!