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How to Create a Pulse Width Modulator

Pulse width modulators, circuits that are used to set the pulse width of an electronic waveform, are used in the design of a wide variety of electronic hardware. Waveform generators, modems and power supplies often include pulse width modulators as part of their basic design. Creating a pulse width modulator can be done in many different ways. One of the easier ways is to use an everyday 555 timer integrated circuit. With the 555 timer, a resistor and a capacitor, you can have your pulse width modulator up and running in just a few minutes.

555 timer integrated circuit
Electronic breadboard
Power supplies, two (five volts)
Breadboard jumper wires (black, red and green)
Variable resistor (0 to 10,000 Ohms)
Variable capacitor (0.05 to 0.2 microFarads)
Waveform generator
Oscilloscope

Instructions

- 1
  Insert the 555 timer integrated circuit into your electronic breadboard. Connect the power supply's positive terminal to the breadboard's power supply bus. Connect the power supply's negative terminal to the breadboard's ground bus.
- 2
  Insert the 555 timer integrated circuit into the breadboard. Connect pin 8 (the voltage supply pin, Vcc) and pin 4 (the reset pin) of the timer together with a green breadboard jumper wire. Connect pin 8 to the power supply bus with a red breadboard jumper wire. Connect pin 1 (the ground pin) of the timer to the ground bus with a black jumper wire.
- 3
  Connect the variable resistor between pin 8 (Vcc) and pin 7 (the discharge pin) of the timer. Connect the variable capacitor between between pin 7 (discharge) of the timer and pin 1 of the timer.
- 4
  Connect the positive terminal of the waveform generator to pin 2 (the clock input pin) of the timer. Connect the negative terminal of the waveform generator to the breadboard's ground bus.
- 5
  Connect the oscilloscope probe to pin 3 (the timer's output pin, the modulated pulse wave form). Connect the ground lead of the oscilloscope probe to the breadboard's ground bus.
- 6
  Connect the positive lead of the second power supply to pin 5 (the control pin, also called the modulation input) of the timer. Connect the negative lead of the second power supply to the breadboard's ground bus.
- 7
  Adjust the variable resistor and variable capacitor so that they are in the middle of their ranges.
- 8
  Turn on the power supplies and the pulse wave form generator. Set the first power supply, the power supply that supplies power to the timer, to 5 volts. Set the second power supply, the power supply that controls the width of the output pulse width, to 3 volts. Set the pulse width generator to produce a square wave with a frequency of 2 kilohertz with a high voltage of 5 volts and a low voltage of 0 Volts.
- 9
  Observe the pulse waveform on the oscilloscope. Vary the voltage level applied to the modulation input and observe that the pulse width increases as the modulation voltage level increases and decreases as the modulation decreases.

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