Simple Square wave Generator


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

Circuit diagram:

GIF

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.

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