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How to Compute a Digital Duty Cycle

In digital electronic circuits, signals typically take the form of rectangular pulse waves. The pulse has a starting point at zero volts, rises rapidly to a maximum, then falls just as rapidly back to zero. The relative amount of time a pulse spends at its maximum may shift; this is known as pulse width modulation. A parameter called duty cycle is the ratio of a pulse wave̵7;s ̶0;on̶1; time to its entire period; engineers express this as a percentage. A pulse with a 50 percent duty cycle is on for half of the wave̵7;s total period.

Things You'll Need

Oscilloscope probe
Oscilloscope
Calculator

Instructions

- 1
  Attach the oscilloscope probe̵7;s BNC connector to the oscilloscope̵7;s BNC male on channel one. Connect the probe̵7;s ground clip to a grounding point of the digital circuit. Connect the probe̵7;s signal clip to the circuit̵7;s output.
- 2
  Turn the oscilloscope and circuit on. Set the oscilloscope triggering to channel one. Adjust the oscilloscope̵7;s horizontal sweep rate and channel one vertical gain until you see several pulse waves on the screen.
- 3
  Count the horizontal division markings on the screen to measure the width of one pulse̵7;s on-time. Note this is the on-time only, not the width of the entire cycle. Enter this figure into the calculator and press the "Divide" key.
- 4
  Count the horizontal division marks to measure the entire width of one full pulse cycle. Begin at the end of the preceding cycle and count until the beginning of the next cycle. Enter this number into the calculator. Press the "Multiply" key, enter 100, then press the "Equal" key. The result is the pulse̵7;s duty cycle as a percentage.

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