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I'd like to visualize the PWM signal from an Arduino Uno board with an oscilloscope.

I'd like to use this layout:

enter image description here

Is this a safe connection?

In other words, might I have problems because the oscilloscope and tha PC's PSU share the same earth ground?

I need to connect the Arduino to the PC by USB cable because I need to run software from the PC to the Arduino.

Update:

I've connected the oscilloscope and it works fine.

When I change the duty cycle percentage (from 0% to 100%) in Matlab/Simulink I can see it directly on the oscilloscope.

update

JRE
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M4Biz
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  • You should be floating your scope regardless. You can get a ground isolation plug pretty cheap. With this setup, the return of your scope probe is connected to Earth through your scope. Shouldn't cause issues though. – user187594 Mar 12 '21 at 16:14
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    @Stiddily No do not suggest floating equipment that is not meant to be connected without grounding, that can be dangerous and cause more damage to equipment if things go wrong. – Justme Mar 12 '21 at 16:39
  • I say the setup is safe. In some situation, having a ground loop can distort the signals, but I don't think this is the case. – linuxfan says Reinstate Monica Mar 12 '21 at 16:41
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    @Stiddily You should not float an oscilloscope unless you really know what you're doing, and if you plan to float your oscilloscope I'd question how much you know what you're doing. – Hearth Mar 12 '21 at 16:53
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    Just here to reiterate, that no, you don't want to float your test equipment for 99.9% of use cases. – Colin Mar 12 '21 at 16:56
  • Yes, this is fine. The only reason it would be a problem is if they *didn't* share the same ground, *or* if you wanted to connect the scope's ground wire to somewhere other than ground. Connecting ground to ground is almost always fine – user253751 Mar 12 '21 at 17:00
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    @Stiddily and others who might consider floating a scope: [Look here for reasons why a floating scope is a bad thing.](https://electronics.stackexchange.com/questions/73991/why-do-we-need-an-isolation-transformer-to-connect-an-oscilloscope) – JRE Mar 12 '21 at 17:03
  • @JRE TIL... My entire office has been floating their scopes for years. Never had issues. Didn't realize this was such a polarizing topic. Thanks for the info. – user187594 Mar 12 '21 at 17:17
  • If I am looking at a relatively low frequency digital signal that is referenced to earth ground, I sometimes don't connect the scope ground. If the noise is unacceptable, then I connect the ground. – Mattman944 Mar 12 '21 at 17:34
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    @Stiddily It of course depends on how the scope is made to float. There are safe ways of doing it, but simply disconnecting the earth from mains plug is by far the worst possible way of doing it. It will make the scope ground to float at half mains voltage referenced to mains earth due to Y caps in the mains supply filter. That's enough to tingle fingers when touching the scope. A test lab managed to damage our expensive prototype by following a test procedure that required to disconnect the scope earth from mains with a special ground lift plug, before poking around the circuitry. – Justme Mar 12 '21 at 19:10
  • @Justme I'll have to see how much Y-cap my scope has. Must be a pretty high impedance to have not fried everything I've tested recently. I already pulled the plug isolator off my scope. I use isolated probes most of the time anyway. – user187594 Mar 12 '21 at 20:09
  • Two things against floating a scope: it's dangerous (unless it's battery powered) and in some scopes it raises a lot the background noise. However, if your signal ground is equipotential with ground there is no issue to start with – Lorenzo Marcantonio Mar 13 '21 at 00:49

2 Answers2

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Yes, this is exactly how the equipment are supposed to be connected.

Earthed/grounded PC, earthed/grounded scope.

Safest for you and the probed equipment, there is no danger of damage.

Even better if both the PC and the scope are connected to same dual wall socket or same power strip, so it can be sure that they are grounded at the strip or wall socket, instead of long wires within the wall if they are on separate wall sockets. It also guarantees that they are powered from the same mains fuse and mains phase.

Justme
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The way you've shown it setup is correct and normal, and will not cause damage to the equipment or distortion of the signals.

Here's a picture of my scope doing exactly what you want to do:

enter image description here

That's a digital output from an Arduino Nano, clocking along at 100kHz.

The scope and the PC were plugged into separate outlets, and the Nano was powered from the PC. I used the PC to send commands to the Nano to change the output frequency.

JRE
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  • What scope is this? It looks like a modern digital display overlaid on top of what either is, or is a very good facsimile of, a CRT beam... I like the look of that a lot, actually! – Hearth Mar 12 '21 at 16:54
  • @Hearth: The image is from [this thing.](https://github.com/JosephEoff/D43) That's a program I wrote to capture images and make measurements from my [D43 analog oscilloscope.](https://josepheoff.github.io/posts/oscilloscope-camera) It is an overlay on top of a live video (web cam) capture from the CRT of the scope. – JRE Mar 12 '21 at 16:58
  • Fascinating! I'll have to look into that when I get home this evening.... – Hearth Mar 12 '21 at 16:59
  • @JRE lol you did what – user253751 Mar 12 '21 at 17:04