This simple but complete Theremin with Inverter Gates is constructed using only two inverter chip plus one regulator IC. This Theremin circuit consist of five functional blocks: power supply regulator, hand controlled oscillator, null oscillator, mixer, and filter. Here is the complete schematic diagram. Theremin with Inverter Gates schematic diagram Voltage Regulator and Circuit Protector The power supply regulator consist of LP2950 regulator IC, which stabilize the voltage from battery to 5V. You can use more popular 7805 IC for this, but since the power consumption of this Theremin circuit is very small, then you can use 78L05 which is smaller. CR1 diode is used to protect from inappropriate battery polarity, shorting the battery voltage together with R8 100 Ohm resistor which prevent the large current when the battery is installed in wrong direction. Although the inverter chip will work well for 9V battery, there is a benefit of using voltage regulation to regulate the...