Oscilloscope Measures PWM Voltage Pt. 1

In the picture above, Oscium’s iMSO-104 and an iPad mini display the pulsed output of an Arduino board’s Pulse Width Modulation (PWM) output. In the foreground, an LED is illuminated by the pulses from the Arduino board. Making an LED light up is a simple use for this circuit, but often it’s also how beginning programmers learn to control the microprocessor – it’s the equivalent of making the computer print “Hello World” on the screen.

The time varying voltage across the LED is also measured by a digital multi-meter (DMM). Although the DMM and iMSO-104 are measuring the same, identical signal, their results couldn’t be any more different. “Well how’s that?” you might wonder. The difference is in how both instruments measure the voltage.

  • DMM: The DMM, or simply “voltmeter”, is an averaging device that produces a result by sampling a voltage for a period of time, and displaying the average value as a single number – with variable precision – on the screen.
  • iMSO-104: The iMSO is an oscilloscope. Oscilloscopes are especially useful for studying and analyzing time varying signals. The pulses displayed on the iPad screen represent the instantaneous voltage measured at each point in the timespan. An oscilloscope can perform mathematical functions on the collected data points that a voltmeter cannot. Oscilloscopes can calculate pulse characteristics like the following: Rise/Fall Time, Peak to Peak, RMS, Mean, Maximum or Minimum, and Pulse Width and Duty Cycle. These calculations aren’t possible with a voltmeter that collects only a single, average, value that represents the signal at a moment in time.

How PWM Works on Dimming LED 

The video below shows the LED getting brighter and dimmer as the PWM output changes with time. The changing PWM voltage is displayed on the oscilloscope screen and the average value is shown on the voltmeter's display.

Learn More About PWM In Next Blog

In the video you see the DMM changing values as the pulses displayed on the oscilloscope change and the LED gets brighter or dimmer. For a deeper look at what’s going, come back next week for installment #2: PWM Voltage Part 2.

Oscium's handheld oscilloscope is now available with universal platform support! So, if you're interested in using the scope on iOS, Android, PC or Mac, Oscium supports you. Please go to iMSO-204x for more information.