LTX Theremin
Thursday, June 18, 2009
The LTX Theremin is a square wave oscillator that reacts to light. This is a fairly simple circuit and a good one for anyone starting out. It uses the popular 556 timer and a few other popular components. (I will supply the parts listed below in the “Parts List” at a cost upon request, while they are available.) These parts can be switched out for others with different values for different sound results. Try recreating this circuit on a breadboard and experiment to create your own modified circuit. Before we start, I am obligated to inform you to wear safety goggles in case solder flings from a wire, and be careful not to burn yourself with the soldering iron. Just to cover all bases, make this circuit at your own risk. It is a very low power circuit and shouldn’t cause any injury, but if your going to be modifying it, you may burn out components or create sparks.
IC Board
Refer to the numbers shown on this diagram when soldering. Each number refers to the entire area outlined in black. So you may solder components or leads to any of the holes within that area. To keep it simple, solder to the points shown in the examples.
Parts List
 |
IC Board |
 |
556 Chip |
 |
0.1uf Capacitor |
 |
220uf Capacitor |
 |
1/4″ Jack |
 |
500k Potentiometer |
 |
Photoresistor |
 |
9 Volt Battery Clip |
Additional Tools and Items
You will also need a soldering iron, solder, wire and wire cutters, a 9 volt battery and a quarter inch connection to an amplification device.
Optional
A speaker can be added by connecting it to pins 3 and 4 of the 1/4″ output jack. A power switch may also be added between the battery clip and the board. Other possibilities exist also, experiment.
Assembly
1. Locate the extra hole next to 13. Make sure this hole is always on the bottom.
2. Place the 556 chip so that the top left pin is in 2. The tab should be on your left and the text right side up. You may have to bend the pins slightly to fit the chip into the board.
3. Solder the 556 to the board.
4. Solder a lead connecting 3 and 16.
5. Solder a lead connecting 8 and 15.
6. Solder a lead connecting 6 and 16.
7. Solder a lead connecting 3 and 4. This can be done from the bottom with a bead of solder.
8. Solder a lead connecting 14 and 18.
9. Solder small capacitor to 13 and 14.
10. Solder LDR between 15 and 18.
11. Solder large capacitor to 7 and 9. Make sure the white stripe is connected to 9.
12. Solder a lead connecting 2 and 6.
13. Solder a lead connecting 2 and 20.
14. Solder pin 1 of the 1/4″ jack to 9 on the board. Solder pin 2 of the jack to 6 on the board.
15. Solder a lead connecting 7 and 12.
16. Solder a lead connecting 11 and 19.
17. Solder pin 3 of potentiometer to 9 on the board. Pin 2 of potentiometer to 15 on the board.
18. Solder battery clip, positive to 20, negative to 13.
19. Connect a battery and hook up a 1/4″ to test for sound.
20. Before soldering the LED, test it by touching the ends to the bottom of the board. Touch it to 11 and 12. When the LED lights up, solder it in that way to the top of the board between 11 and 12.
Category: