Simple Theremin Circuit Using Inverter Gates

Here’s a design circuit for simple theremin circuit is constructed using only two inverter chip plus one regulator IC. This Theremin circuit is consists of five functional blocks: power supply regulator, hand controlled oscillator, null oscillator, mixer, and filter. This is the figure of the circuit;

The power supply regulator is consists 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 battery voltage at lower voltage level, that the voltage will remain constant for until the end of battery life. This will avoid frequency drift of the Theremin’s null oscillator  which should be carefully adjusted to zero the output frequency, which can be affected by the supply  voltage.