Simple Square wave Generator

Three switchable frequencies: 100Hz, 1KHz, 10KHz
1.5V battery operated, minimum parts counting

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.

Parts:

• 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.)

Notes:

• If a precise 50% duty-cycle is needed, trim R1 and monitor the output wave form by means of an oscilloscope.
• A good 500mV peak-to-peak square wave is provided even at 1V supply.