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