Radio Transmitter

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Wednesday, April 1, 2009

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.

  • 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.)

  • 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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