This is a Simple Theremin Volume Control that Requires No Batteries!
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Click here for my improved favorite=> illumination Volume Control
The Audio In/Out of this volume control is at a microphone level of less than .6 volts. Your must reduce the output of your Ultimate 2b to a minimum using Gain 2 which is Pot 2.The output of this volume control is at very low level and must be fed into an amplifiers microphone input. It will not drive amplified computer speakers directly.

Theory: The solar cell maintains a voltage above 1 volt when exposed to normal room lighting. This keeps the transistor forward biased, which in turn allows the audio signal to pass freely. When the light level begins to drop (your hand covers or shadows the cell) the transistor begins to cut off. A  6" window of control from Full Volume to Total Cut Off is possible. This On/Off transition is good with little distortion of the signal.

Use shielded cable on the Audio Input and Output leads.    Click on photo for a close up board view.

The output can only drive a microphone input.
volume.mp3   (88 kb)   Fade In - Tone - Fade Out - Quiet - On - Fade Out 
I used a 3" x 3" diameter gold paper tube around the solar cell to narrow the available light to the overhead white living room 8' ceiling. Full volume to cutoff  can be a hand movement > 6" with medium room lighting.
Note:  If you mount the solar cell in a small box or 3" tube with an opening on one side, you can use a living room floor lamp 10' away as the projected light beam to keep the "volume on". Casting a shadow between the two onto the solar cell with your volume control hand would then quiet the volume. This method allows you to put the volume control in any position or location, it even allows you to play with a single hand pitch/volume. Your hand controls the volume mysteriously in open air, no volume hoop. This is how I get those crisp notes on a musical scale in some of my sound bytes. Halogen lamp light works best to minimize any 50/60 hz hum.

Improved Construction

In the schematic at the left Pot 1 is added to reduce the signal strength of the input so this optical volume control can be used with any source of audio output.

The output of the volume control can only drive the microphone input of an amplifier.

Here is the PDF (172k) for this design so you can make an etched circuit board.

Etching your own PC Board

Thank you Shannon for the input.

PDF (125k) layout. Paste this graphic onto the top side of a plain perf-board for component layout & hand wire, no etching. Cat.# 276-147 $4.29
Attenuator
Use the above circuit as a Custom Level Adjustor for any Theremin output to properly drive any Amplifier's input level. Just leave off  R1, C1, Solar Cell and Q1 which is jumped with a wire from the emitter to collector. PDF (125k)

Solar Cell 

I removed it from a Malibu sun-powered yard light - Model LZ1 D $9.98  and also the Malibu Model  LZ6 $8.98 USD, these are located in the Electrical Section of the store.

You can purchase this solar cell at Home Depot or Lowes  Malibu sun-powered yard light  

Take the Solar Cell out of the box and tap on it with a coin and make sure it is not glass!  (It Should be Epoxy)
  
The above solar cells are the most effective I found. They output in the 2 to 3 volt range in sunlight.  These are available year round in California but only in the Spring & Summer of many other states.

The Radio Shack solar cell  276-124  will not work and the Malibu LZ403 L will not work, it is made of glass.

 

All Parts below purchased from Radio Shack

Transistors
Q1 = 2N2222 or any general purpose NPN transistor. 
If you have a meter to measure Hfe "The higher the gain or Hfe the better at lower light levels! "
An Hfe of 200 is good, but an Hfe of 400 is slightly better at remaining On at lower light levels.
Radio Shack has a pack of 15 Cat # 276-1617  $2.49 USD

Resistor
R1 =  100K ohm  (brown - black - yellow - gold)

Pot 1 = 1K    271-280  $1.29 USD 

PC Board Terminals 2-Position Cat #  276-1388 $2.29 Optional - Pack of 4
Project Box  4x2x1  Cat # 270-1802 $2.69  Optional

Capacitors
C1 = 1 uf  Tantalum  Cat # 272-1472  $1.49 USD 
(This capacitor smoothes out any 50/60 hz ripple picked up from indoor lighting, any larger would slow down response.)

C2 = Ceramic capacitor .22 uf  or 224 marking. Use the largest non-electrolytic you have, 1 uf  is ideal.
In the photo I use a 1 uf  Metalized-Film Capacitor  Cat # 272-1055   $1.49 USD

Circuit Board - General Purpose   Cat # 276-159  $1.99 USD "seen in the very top photo."

or use Cat.# 276-147 $4.29 PDF (125k) generic board

or  etch your own with this  PDF  (172k)

Audio In/Out Cord
The J2 Audio Out works best when fed into a amplifier with a higher input impedance.
I cut apart a 36" Shielded phono extension cable. Cat # 420-2361  $2.99 USD

Last Updated 08.26.05