Simple Square wave Generator

Three switchable frequencies: 100Hz, 1KHz, 10KHz

1.5V battery operated, minimum parts counting

Circuit diagram:

Squarewave generator


R1____________560K   1/4W Resistor
R2____________680R   1/4W Resistor
R3______________2K2  1/4W Resistor
R4____________150K   1/4W Resistor

C1_____________12nF   63V Polyester Capacitor
C2______________1n2   63V Polyester Capacitor
C3____________120pF   63V Polystyrene or ceramic Capacitor
C4,C5__________10µF   25V Electrolytic Capacitors

Q1,Q2________BC549C  25V 100mA NPN High-gain Low-noise Transistors

SW1____________SPST  Slider Switch
SW2____________1 pole 3 ways Rotary Switch

B1_____________1.5V Battery (AA or AAA cell etc.)


This simple circuit generates a good and stable 1V peak-to-peak square wave at 100Hz, 1KHz and 10KHz using a single 1.5V cell as power supply.
An useful feature of this circuit is that frequency changes can be obtained by switching only one capacitor at a time.
Current consumption is about 600µA.