Simple Square wave Generator

Simple Square wave Generator




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


1.5V battery operated, minimum parts counting





Circuit diagram:


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.)



Comments:


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.
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.