Learning to 'scope with Multicomp

20 Mar 2022

I recently received a Multicomp MP720015 from element14 as part of a contest prize. It's a very nice little unit, but I know nothing about oscilloscopes so it's a learning curve. I mean a learning opportunity

Luckily for me, baldengineer was kind enough to produce a few videos and blogs about the subject! Thank you James! your tutorials are exactly what I needed

So I pulled out an extra Arduino Uno I have here to get the very first basic pattern to test: the Blink sketch.
(I don't recall if I had to speed up the blinking to get this result)

Turns out that gives a nice easy square wave (? is that the term?) to look at. Yay it works!

Then I tried with AnalogWrite, as James did in his video, and all I got was muckymuck garbage to look at. hmm... why?
I gave up that evening as it was getting late, but later realized it was likely because I was using pin D13 which has the built-in LED on it. I specifically used it so I could see the LED at the same time as the scope result, but I think it was affecting the output voltage levels. Yes, I did press the auto-set button a few times without luck.

So today I changed the sketch to use pin 9, and success! I can now see how PWM looks:

Scope showing Arduino AnalogWrite

I haven't had any luck trying to scope fading with analogWrite, and I don't know if that's a limitation with the scope or with the user :D

Fun start though.

I also tried out the DMM (multimeter) functions, and it appears to be nice, stable, and accurate. It does take much longer to start up than my regular multimeters, so for quick one-off readings I'll likely just use those. For more involved work I can see it being useful especially when also using the scope functions.

-Nico

Top Comments

DAB over 3 years ago

An oscilloscope can be lots of fun, as is the world of analog devices.

There is a much larger world out there than just ones and zeros.
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baldengineer over 3 years ago
> I haven't had any luck trying to scope fading with analogWrite, and I don't know if that's a limitation with the scope or with the user.

It depends on how fast you change the analogWrite() value in code. If you put the analogWrite into a loop, across multiple triggers you should see the pulse width changing.
```
for (int x=0; x<255; x++) {
  analogWrite(9,x);
  delay(1); // see difference with and without
}
```
With the 1 millisecond delay, you'll never see the PWM change on the screen (in a single acquisition.) Without, you *might* catch it. Either way, you'll see the pulse width change as the scope re-triggers.
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Jan Cumps over 3 years ago

> haven't had any luck trying to scope fading with analogWrite

You should see the high part of the signal go narrower and broader, when the analogWrite() vallue changes. The PWM frequency stays the same.
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aspork42 over 3 years ago

Awesome! Looks like a cool scope!
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ntewinkel over 3 years ago in reply to baldengineer

> "Heads up, pin 13 does NOT support analogWrite()"

Aaahhhhh. ok that makes a lot more sense now - I wondered why the LED would make that big a difference. I forgot about that detail of not all pins supporting PWM.

Thanks for the clarification

edit: you know, the funny thing is that for pin 9 I specifically verified that it was capable of PWM (checking for the ~ as you mentioned), but I totally failed to think of looking at D13 for that detail
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