The light theremin

A theremin is an instrument that can be played by changing the proximity of hands to its sensors. Traditional theremins produce classic spacey and eerie sounds commonly associated with sci-fi and horror films. The version discussed here is a simple optical variant. It utilizes a specialized integrated circuit (IC) chip known as a 555 timer chip, which is typically a small black chip found on a breadboard. While it is more specialized than the operational amplifier chip used in previous projects, it shares some similar functionalities. The construction of the circuit should be based solely on the provided schematic. The orientation of the 555 timer chip is crucial; when viewed from above, one end of the chip will have either a notch or a circle that corresponds to the schematic. Each pin of the chip must be examined individually to determine if a component (such as a resistor, jumper, capacitor, or CdS photoresistor) is connected to it. If a component is identified, one leg should be connected to the appropriate pin of the 555 timer chip, while the other leg must be connected to either another pin on the chip, a 9V power source, or ground (0V).

The theremin operates by detecting changes in capacitance based on the proximity of the player's hands to the sensors, which in this case are facilitated through optical means. The 555 timer chip serves as the core of the circuit, functioning in astable or monostable mode to generate audio signals that can be modified by the inputs from the optical sensors. The circuit design typically includes resistors and capacitors that define the timing characteristics of the 555 timer, thereby influencing the pitch and tone of the sound produced.

In constructing the circuit, attention must be paid to the pin configuration of the 555 timer. The standard 555 timer has eight pins, each serving specific functions, such as triggering, resetting, and outputting the signal. For instance, pin 1 is connected to ground, while pin 8 is connected to the positive voltage supply. The configuration of resistors and capacitors connected to pins 2 (trigger), 3 (output), 6 (threshold), and 7 (discharge) will determine the frequency of the oscillation and, consequently, the sound produced by the theremin.

The optical sensors, such as CdS photoresistors, will vary their resistance based on light intensity, allowing for modulation of the sound output as the player's hands move closer or further away from the sensors. By adjusting the values of the resistors and capacitors in the circuit, the user can customize the responsiveness and tonal qualities of the theremin, creating a unique sound experience. Proper soldering and connections are essential to ensure reliable operation and to minimize noise or interference in the audio signal.A "theremin" is an instrument you can play just by changing the proximity of your hands with respect to the instrument`s sensors. Traditional theremins generate the classic spacey, spooky sounds from sci-fi and horror films. Ours is a simple optical version. We`ll use a separate IC chip for this, called a "555 timer chip" (the small black chip on your breadboard). It`s a bit more specialized than the op-amp chip we used for the last build, but they can do similar stuff. This time, try to build the circuit based on the schematic alone. It`s not hard as long as you know the orientation of the 555 timer chip. Looking down from above, there should be a notch or a circle at one end of the chip which corresponds to the notch on the chip in the schematic.

All you need to do is look at each pin on the chip one at a time. Is there a component (resistor, jumper, capacitor, CdS photoresistor, etc. ) connected to it If yes, find that component in your kit. Plug one leg into the 555 pin. Then figure out if the other leg of the component plugs into a different 555 chip pin, or plugs into 9V, or plugs into 0V, etc. 🔗 External reference