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I am beginner in electronics and I would like to measure 12 kHz sine wave pwm signal on the output pin of my microcontroller. My problem is that I am not able to setup the digital oscilloscope RIGOL MSO1104z (User's guide) in such a manner that I am able to see the signal. Firstly I tried to use Auto set function but without success (the signal is unstable). Then I tried to set the oscilloscope by myself (I set the trigger level and hold off time but there is only some transient waveform on the screen). I have been reading the User's guide to the oscilloscope but there are no practical examples how to set the oscilloscope for common measurements. Please can anybody give me an advice how to set up the oscilloscope for my measurement? Thanks a lot in advance. enter image description here enter image description here enter image description here enter image description here

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  • \$\begingroup\$ Please provide more about your setup because otherwise it's too broad to tell anything. Maybe you just wired things wrong, maybe the problem isn't in your scope. \$\endgroup\$ – Artūras Jonkus Jan 3 '17 at 8:21
  • \$\begingroup\$ Your top plot seems to show what you want. What's the problem? \$\endgroup\$ – Olin Lathrop Jan 3 '17 at 15:10
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There are different ways to trigger your scope.

  1. Use your scope in single-shot operation. Trigger once then work on the captured waveform.
  2. Use the math functionality (page 6-21) with a low-pass filter to filter the PWM signal. With the proper cutoff-frequency you should be able to see the sinewave. You could display the PWM on another channel and overlay the PWM with the filtered signal. You should be able to trigger on the math channel. Update: Triggering on the math channel is not possible with this scope.
  3. Use an external trigger. The scope has a trigger input that you can use. You could program your microcontroller to generate the trigger signal on another pin that you can feed to your scope (see chapter 5).
  4. Filter the PWM using a two-stage RC-filter and trigger on the sinewave. Use two channels the see the PWM and the filtered signal.

Actually you should try all of these since this a nice exercise that will help you to get to know your scope better.

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  • \$\begingroup\$ Hello Mario, thank you very much for your help. I would like to use the first option. What should I do exactly? Should I push SINGLE button and then should I push the FORCE button? \$\endgroup\$ – Steve Jan 3 '17 at 11:28
  • \$\begingroup\$ In single mode the scope should stop after the first acquisition. If the scope doesn't trigger you can use the FORCE button. \$\endgroup\$ – Mario Jan 3 '17 at 11:47
  • \$\begingroup\$ I received following waveform (please see the attachment in my first question). There is some noise present. So I tried to use the second option but there is a problem with the cutoff frequency which is limited to 1 kHz (I have been trying to generate 50 Hz sine wave). I have doubts about the correctness of my measurement. My control board is supplied from the separated laboratory source and the scope is supplied from the mains. I connected the probe's crocodile jack to the source's minus pole. Is it correct? \$\endgroup\$ – Steve Jan 3 '17 at 13:32
  • \$\begingroup\$ I think the measurement setup is OK. The PWM signal doesn't look like a sinewave though, the duty-cycle changes to quickly. Maybe start with a simple ramp or a fixed duty-cycle (0%, 50%, ...) to check your setup. \$\endgroup\$ – Mario Jan 3 '17 at 13:53
  • \$\begingroup\$ I have attached new waveforms for 50% duty cycle and 25% duty cycle to my question. They look alright although the frequency isn't 12 kHz but only 6 kHz. But it is a problem in PWM periphery settings. I also attached maybe better sine wave pwm signal. \$\endgroup\$ – Steve Jan 3 '17 at 15:12

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