Oscilloscope newbie, I have no idea what i am doing  - Page 1
Forum section: electronics / beginners

author: littlebill
author_rank: Regular Contributor
timestamp: September 12, 2022, 01:40:26 am
content: I don't understand whats going on. I have a new pico2204a, that I am trying to learn on.it seems the minute i go over 1v on it, it slows way down and simply won't trigger on anything.I am using a desktop psu in the screenshot below, when i turn it off and the range is 50mv the scope is flying and triggers perfectly, I turn it on, and it moves like 1 frame a second on auto mode, but never triggers regardless of what mode I am using.screenshot below, can someone send me in a direction. I don't understand why it works perfect with the psu off, or testing with the awg port.

author: ataradov
author_rank: Super Contributor
timestamp: September 12, 2022, 02:35:38 am
content: You have a trigger on the failing edge only. So it triggers on the failing edge and does not notice your rising edge.In the trigger section you see the symbol for the edge next to "A".And auto mode looks for the trigger condition and automatically refreshes anyway if there is no trigger after some timeout.

author: littlebill
author_rank: Regular Contributor
timestamp: September 12, 2022, 02:57:12 am
content: its not triggering at all? single shot shows it running non stop

author: ataradov
author_rank: Super Contributor
timestamp: September 12, 2022, 02:58:49 am
content: I don't understand your question. In the configuration as shown on the screenshot, it would only trigger on the falling edge.

author: littlebill
author_rank: Regular Contributor
timestamp: September 12, 2022, 03:07:47 am
content: in that photo, its not triggering, no matter where i put the trigger it does not trigger. I am starting to believe that the waveform is too small to trigger, but that is simply a guess.

author: ataradov
author_rank: Super Contributor
timestamp: September 12, 2022, 03:09:05 am
content: What it is supposed to trigger on? You have a DC signal. You described that when you cause a trigger condition by powering on and off, you see it trigger.

author: WattsThat
author_rank: Frequent Contributor
timestamp: September 12, 2022, 03:16:56 am
content: Looks like noise on a dc signal that is not constant.Start with a signal that is predictable, not some unknown dc source with switching noise on it that is only 100 millivolts floating on top of ~7.5 vdc.It looks like the scope has a function generator built-in. That’s a much better place to start.

author: littlebill
author_rank: Regular Contributor
timestamp: September 12, 2022, 03:34:36 am
content: I'm trying to trigger on that noise. If I disconnect the psu, it will trigger flawlessly on the induced? noise, that's why i thought it should be able to trigger with the psu on.

author: ataradov
author_rank: Super Contributor
timestamp: September 12, 2022, 03:35:10 am
content: You can't. There is no way analog trigger will trigger on single LSB noise. This is also pointless. This is not a real noise, this is is just inaccuracy of the ADC.

author: littlebill
author_rank: Regular Contributor
timestamp: September 12, 2022, 03:36:13 am
content: Quote from: WattsThat on September 12, 2022, 03:16:56 amshouldn't single shot be able to fire on a inconsistent pattern?i did start with awg, and it worked fine, thats why i was trying to understand why i couldn't trigger on the noise of my psu.I did find a digital car charger, and I can see that, again I am new at this, not sure what i was suppose to be expecting

author: littlebill
author_rank: Regular Contributor
timestamp: September 12, 2022, 03:37:09 am
content: lsb?

author: ataradov
author_rank: Super Contributor
timestamp: September 12, 2022, 03:38:43 am
content: Quote from: littlebill on September 12, 2022, 03:36:13 amThe change you see here is the absolute minimum ADC reading can change. The trigger is a separate analog comparator, there is no way it will be able to notice it.

author: ataradov
author_rank: Super Contributor
timestamp: September 12, 2022, 03:39:27 am
content: Quote from: littlebill on September 12, 2022, 03:37:09 amLeast Significant Bit. The minimum amount ADC output can change in response to the analog input change (or noise).Basically, simply because you can "zoom in" on the signal, does not mean you should. And PC-based scopes make it far easier than it should be to the point where it is annoying.I would say, if you are a beginner, make sure that the 0 (ground) level is always on the screen along with the signal. This way you can't zoom into a pointless territory.

author: jasonRF
author_rank: Regular Contributor
timestamp: September 12, 2022, 08:42:25 am
content: I have a 2204a also. The other comments here are spot on, of course. The issue is that it is like most scopes in that in has 8-bit resolution. On mine I find that there are usually around 225 levels for each vertical scale setting. You are set at +/- 10 V, so the LSB is about 20V/225 or a little less than 100 mV. It will need AC signals that are probably at least 10-20 times that size to reliably trigger.If you want to see small-level noise that may be riding on top of a DC signal, it can sometimes be necessary to AC couple the channel. That will get rid of the DC part of the signal so you use a more sensitive vertical setting to look at the small noise voltages. With your example, on AC coupling you may be able to use a setting around +/- 100 mV, which would give a LSB a little under 1 mV. This will be 100 times more sensitive than what you are doing by trying to zoom in on the signal acquired with a +/- 10V setting.

author: littlebill
author_rank: Regular Contributor
timestamp: September 12, 2022, 12:24:57 pm
content: guys appreciate the info. I figured later that might be trying to zoom in on something too small to trigger. but its new to me. I bought it for some automotive work, appreciate all the responses

author: littlebill
author_rank: Regular Contributor
timestamp: September 12, 2022, 12:26:33 pm
content: Quote from: jasonRF on September 12, 2022, 08:42:25 amI do wish the pico software would "lock" me out of settings that the scope is not capable of, the comment above may make sense to you, but most of this is still gibberish to me.

author: Old Printer
author_rank: Frequent Contributor
timestamp: September 12, 2022, 02:44:27 pm
content: Congrats on your new scope. It's a pretty steep learning curve, but don't get too frustrated, it will come a little at a time.

author: james_s
author_rank: Super Contributor
timestamp: September 12, 2022, 05:12:48 pm
content: Quote from: littlebill on September 12, 2022, 12:26:33 pmThere is no reason for it to do that, all oscilloscopes will let you set them up in a way that they are giving you garbage measurements, that's just how oscilloscopes work. They are expected to be used by people who know what they're doing. There are lots of tutorials out there on how to use a scope, it's a complex and powerful instrument that takes practice to use effectively.

author: rstofer
author_rank: Super Contributor
timestamp: September 12, 2022, 07:19:06 pm
content: There's a scope tutorial linked to the top of this forum.

author: littlebill
author_rank: Regular Contributor
timestamp: September 12, 2022, 09:08:20 pm
content: Quote from: rstofer on September 12, 2022, 07:19:06 pmYea im trying to get there. this is for automotive for me, so I've been watching scanner danner on youtube to get where I need to be.

author: Jamackey
author_rank: Newbie
timestamp: September 20, 2022, 09:15:49 am
content: Hi littlebill.Have you tried AC coupling the signal? This will put the noise around 0V (GND) filtering the 7V DC allowing you to use the voltage range more effectively (500mV or so).The simple trigger has a small amount of hysteresis stopping it triggering on a too small of a change so it may not be seeing that low resolution noise voltage in your gif.The scope doesn't have enough Voltage Resolution to give you enough detail at +7V as it's only 8bits of resolution. (255 points over 10V range vs 255 points over 500mV range).Feel free to have a look at a basic tutorial video I did for Pico Technology on PicoScope 7 here: