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How to Create a Variable Output Frequency

Variable frequencies are created when an oscillation or waveform is made to change the number of times it is repeated in a certain interval. They are useful because they can help measure voltages, test devices and calibrate instruments.

Variable frequencies can be produced with an integrated circuit chip or IC, such as a 555 timer. The frequency range is set with a combination of resistors and capacitors. Use a mathematical formula to determine which values to choose. To change the frequency of the circuit, use a potentiometer, which is a variable resistor.

Things You'll Need

555 timer IC
Piezo buzzer
10k-ohm resistor
50k-ohm potentiometer
0.01uF capacitor
0.1uF capacitor
Breadboard
Jumper wires

Instructions

- 1
  Study the equation to determine the frequency of the 555 oscillator circuit. The formula is f = 1.44/(R1 + 2R2)C, where f is the frequency, R1 is the first resistor, R2 is the second resistor, and C is the capacitor. For this circuit, R1 represents the potentiometer.
- 2
  Use the frequency equation to determine the range of the circuit. When the potentiometer has a value of 50k, the frequency is 1.44/(50k +2*10k)(0.1) = 206 hertz. This is the minimum value the circuit can produce. When the potentiometer is set to 0, the frequency is 1.44/(2*10k)(0.1) = 720 hertz, which is the circuit̵7;s maximum value.
- 3
  Place the 555 chip inside of the circuit. Insert it so all of its pins are in different columns, and so it faces left. Select two rows or columns on the breadboard that will function as voltage and ground sources.
- 4
  Connect Pin 4 to the voltage source with a jumper wire. Connect Pin 8 to the voltage source, also. Place the 0.01uF capacitor between Pin 5 and ground, and attach Pin 1 directly to ground.
- 5
  Add a jumper wire to connect Pins 2 and 6. Attach the 10k resistor between Pins 7 and 2. Place the 0.1uF capacitor between Pin 2 and ground.
- 6
  Connect the potentiometer̵7;s wiper to Pin 7. The wiper is the component̵7;s middle lead. Attach one end of the potentiometer to the voltage source, and attach its other end to ground.
- 7
  Listen to the frequency changes. Connect the positive side of the buzzer to the chip's output at Pin 3, and connect the negative side of the buzzer to ground. Place the battery inside of the holder, and then attach the holder̵7;s red lead to the voltage source, and its black lead to ground. When the potentiometer̵7;s knob is turned, the buzzer̵7;s tone will change.

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