Introduction to measuring with a Digital Oscilloscope (DSO138)

Thread Starter

q12x

Joined Sep 25, 2015
609
I received today this DSO138 1612183867761.png ; this is the exact image of it and how I actually receive it (without acrylic case).
But very well packaged and lots of foam, very good.
- DSO138 is my first performant oscilloscope. Tell me anything I should know using it. Tips and tricks, the most used cases that you use it, general / most common measurements. Most dangerous mistakes, what not to make/measure. Stuff like that. I have no idea about anything yet. Hopefully, with your help I will start to get more familiar with it.
- Thank you and make it good for me.
 

KeithWalker

Joined Jul 10, 2017
1,778
The DSO138 is a useful little tool as long as you are aware of its limitations. It comes with a printed instruction sheet called "How to use". Read this carefully and keep it with the scope for reference. On the bottom right corner of page 3 is the spec sheet. This is where you will learn the limitations of it. Note: The maximum input is 50V. Respect that or you will turn it into a book-end.
At the bottom left, in the operations section is the "V pos alignment" you will need to perform this each time you power up the scope because otherwise, there will be a DC offset on the voltage levels displayed.
In general, the scope is a little awkward to use until you get to know it better. I use mine quite often for quick measurements away from my work bench where I have my Analog scope. If you get a x10 probe for it, you will be able to make measurements up to 500V. I recommend that you buy an acryllic case for it.They are not very expensive and it would protect the exposed electronics. It is a bit difficult to line up all the switch actuators at the same time when you are assemble it but it is worth the effort.
Have fun.
Keith
 

MrChips

Joined Oct 2, 2009
23,505
If you are new to using any kind of oscilloscope there are some basics that you need to learn.

Every oscilloscope has three sections:

1) Vertical amplifier - to record input voltages on the Y-axis
2) Horizontal sweep - to determine your time measurement range on the X-axis
3) Trigger circuitry - to set up when you want to start measuring

#3 is the most important part and the most difficult to learn and master.

I will explain all of these later in another post.

Oscilloscopes can measure constant DC voltages or changing voltages that we call AC. We will get into this in more detail later.
Your DMM is better when measuring DC voltages. It is more accurate. It is also better at measuring 50Hz/60Hz line voltages.
Your DMM is not adequate for capturing voltage information that have short spikes, sharp edges, random or periodic fluctuations, music waveforms, etc. This is where the oscilloscope becomes very useful to the point of being essential.

Take the time to learn everything you need to know about your oscilloscope and it will become your #1 best electronic tool and your best friend.
 

dl324

Joined Mar 30, 2015
12,871
Keep in mind that the input impedance of this scope is lower than your DVM. You can't put it on a high impedance node like the 10Gohm on the input of your amplifier; even with a 10X probe.

Triggering will be better with at least a major division or so of vertical deflection.

The bandwidth of the scope is 100kHz 200kHz for sine waves. I was surprised that it could give me the frequency for a 10MHz oscillator (but couldn't display the waveform).

EDIT: corrected bandwidth
 
Last edited:

SamR

Joined Mar 19, 2019
3,400
Some time ago I built one of those kits with the case. You might be better without the case and it fits poorly especially the switches. First thing you might consider is a probe instead of the gator clips. Can't say much as to accuracy as I sent it to my son who has never used it.
 

Thread Starter

q12x

Joined Sep 25, 2015
609
If you are new to using any kind of oscilloscope there are some basics that you need to learn.
Every oscilloscope has three sections:
1) Vertical amplifier - to record input voltages on the Y-axis
2) Horizontal sweep - to determine your time measurement range on the X-axis
3) Trigger circuitry - to set up when you want to start measuring
#3 is the most important part and the most difficult to learn and master.
I am very new to osciloscopes. BUT, I did some homework, long before buying it, by watching a lot of youtube videos on how to use it and when to use it. I have a general idea, but I am 0 at practice, so even I have an idea of all its functions, when I start actually measuring something with it, I forget everything and I get weird results. Thats why I need your help. To guide my ass in some very simple (for you) circuits to analize and from which you have that kind of experience, you are certain you get "that" result and not others (like I most probably will). Thank you.

The maximum input is 50V. Respect that or you will turn it into a book-end.
"V pos alignment" you will need to perform this each time you power up the scope because otherwise, there will be a DC offset on the voltage levels displayed.
If you get a x10 probe for it, you will be able to make measurements up to 500V.
I recommend that you buy an acryllic case for it.They are not very expensive and it would protect the exposed electronics.
Excellent answer, perfect on what I need. Thank you very much.
Please send me a link with your x10 probe.
For now I will build a cardboard case for it. In the future, when I will be able to earn money, I will certainly buy it's plastic case. Your advice is very good. But I can't make money with what I usually do, so im very limited and restricted. I waited probably 10 years until mister @dl324 insisted to take one. And I am happy I listen. Sometimes a kick in the butt is a step forward. Especially for me.
Tell me more , what should I test as a beginner and will give me some insight about how useful it is. Right now with my 0 experience I have, for me is no more than a DMM. I know im stupid, but is the truth.

Keep in mind that the input impedance of this scope is lower than your DVM. You can't put it on a high impedance node like the 10Gohm on the input of your amplifier; even with a 10X probe.
Triggering will be better with at least a major division or so of vertical deflection.
The bandwidth of the scope is 100kHz for sine waves. I was surprised that it could give me the frequency for a 10MHz oscillator (but couldn't display the waveform).
I dont have an old school amplifier. I only have a comercial PC only amplifier 5+1 and the only output from it is the headphones and in the back of it, to each speaker. I only keep 2. Probably you are refering to use it to 1 of these speaker outputs?
Mister @Audioguru again suggested me to use 2 channels for stereo signals from an audio output. It's a briliant idea, but I think my osciloscope has only 1 channel. At least this is what I can tell for certain about it. For the second channel I'll have to buy a second dso138. But somewhere in the far future. Very good test to make. I will test it with the headphones output, if is no danger as you say it might be.
From what I understand, as many channels you have, the best your tool is.
Im very new to triggering, major division, vertical deflection,bandwidth, measuring frequency. Here is an idea, I can measure some frequency with it from a crystal or RC. Right? I need to start get experience with it thats my point here.
Thank you, as always.

First thing you might consider is a probe instead of the gator clips. Can't say much as to accuracy as I sent it to my son who has never used it.
Please send me a link with your (similar or the same)probe that you mention.
 

dl324

Joined Mar 30, 2015
12,871
I dont have an old school amplifier.
I was referring to the amplifier you're using for your LED project.
use 2 channels for stereo signals from an audio output. It's a briliant idea, but I think my osciloscope has only 1 channel.
There's a modification on GitHub that lets you add a second channel by adding some hardware and updating the firmware. It costs you half of your bandwidth. When I mentioned a 100kHz bandwid, I should have said 200kHz.
From what I understand, as many channels you have, the best your tool is.
Two channels are often needed. If you only have one, you try to get by with what you have.
 

MrChips

Joined Oct 2, 2009
23,505
Your DSO138 is a single channel oscilloscope.
For two channels, having an second DSO138 does not cut it. The reason you would want two channels is so that you can compare two signals on the same screen on the same time base (X-axis) and in phase (triggered by the same event).

For now, one channel is better that no channel. A blind man would be happy to have one working eye!

Input impedance is important. You want to minimize any loading you place on your circuit under test. Your DMM has 10MΩ input resistance. A typical oscilloscope has 1MΩ input and so is the DSO138. For now this good enough. You can use the alligator clips that comes with the scope. A probe is better when you just want to make some quick measurements same as using the probes on your DMM. You can make your own probe using the plastic part of an old pen. You want the grounding probe to be an alligator clip. With a good scope you want to get a x10 probe. This increases the input resistance to 10MΩ. Unfortunately, it also reduces the input signal by a factor of 10. For now, use what you have.

We will talk about proper grounding later.
Also we will discuss DC vs AC.

For now, play with the scope with just your finger touching the RED input lead. Play with the voltage range, time scale and triggering.
 

Thread Starter

q12x

Joined Sep 25, 2015
609
Your DSO138 is a single channel oscilloscope.
For two channels, having an second DSO138 does not cut it. The reason you would want two channels is so that you can compare two signals on the same screen on the same time base (X-axis) and in phase (triggered by the same event).
For now, one channel is better that no channel. A blind man would be happy to have one working eye!

Input impedance is important. You want to minimize any loading you place on your circuit under test. Your DMM has 10MΩ input resistance. A typical oscilloscope has 1MΩ input and so is the DSO138. For now this good enough. You can use the alligator clips that comes with the scope. A probe is better when you just want to make some quick measurements same as using the probes on your DMM. You can make your own probe using the plastic part of an old pen. You want the grounding probe to be an alligator clip.

We will talk about proper grounding later.
Also we will discuss DC vs AC.

For now, play with the scope with just your finger touching the RED input lead. Play with the voltage range, time scale and triggering.
Excellent explained ! Bravo. I love it.
I actually finger it at the red probe. Ive also played with all the buttons and I cycle through all the selection options it provide. It also remembers my last setting, after I restart it. That is good if I know what Im doing.
Lets get into the bread, and start measuring something.
Ok. Let me know when you are ready to step through all the controls and settings.
No need since I already know the majority of them from my watched movies on youtube. THis is way to basic for me, im over it already.
Using them in practice, with 1 or 2 examples, that is the thing I want to get good at.
Your picture is very good explained, I like it. Especially for the trigger things that I am not very familiar with. Its a new thing for me.
 
Last edited:

Thread Starter

q12x

Joined Sep 25, 2015
609
There's a modification on GitHub that lets you add a second channel by adding some hardware and updating the firmware. It costs you half of your bandwidth. When I mentioned a 100kHz bandwid, I should have said 200kHz.
Two channels are often needed. If you only have one, you try to get by with what you have.
Yes I understand the 1 channel part. Very interesting thing you find with the 2 channels. For now, as you mentioned, I'll have to get used to what I have and most important to learn to use it in a most decent and normal way (and safe way). Your finding is very good, but is too advanced for me right in this moment and too risky also. Will leave this upgrade for later when I will be more sure on my feet with it. Next, think on some circuit to test. Simple and eficient , just as I like it.
Can I measure 220VAC with it? Iwas told is maximum to 50V on its probes but... Im still asking to get a decisive NO. What if I add myself a 10k resistance between the probe and the hot wire. Im not doing anything, just asking stupid questions until I will be able to ask the smart ones. Heh.
 

SamR

Joined Mar 19, 2019
3,400
Here is a typical good quality inexpensive probe. Note that although it is for 100MHz having a higher rated probe than the scope has a small advantage. And don't believe the Tektronics and HP BS as these are generic probes of decent quality. Basically the same probes shipped with chinese mfg scopes. Cleqee has a decent reputation but they don't make them, only paste their label on them..
1612216786455.png
 

MrChips

Joined Oct 2, 2009
23,505
For now, stay away from 220VAC. We want you to stay around a bit longer.

Wire up a 555-timer oscillator circuit on your breadboard and use the DSO138 to analyze the circuit by looking at the square wave output on pin-3 and the control signal on pin-6.
 

Thread Starter

q12x

Joined Sep 25, 2015
609
Here is a typical good quality inexpensive probe. [picture]
Excellent and thank you! I will search for it today.
By the way, whats the difference between a normal P6100 osciloscope probe and these aligators? They both have the same connector (i hope). What does a P6100 probe have more than these aligators? Or if I change the red alligator to a stick probe as mister @dl324 suggested? And I will consider it in time. Again, sorry for the stupid questions. But this is new to me, so I must ask. If not me, who?
 
Last edited:

Thread Starter

q12x

Joined Sep 25, 2015
609
With a 10X probe. You'll have to do the divide by 10 mentally.
If your power supply is isolated from Earth ground you don't need to worry (as much) about where you put the ground lead.
Exactly my problem ! When to check or what to check? The earth? the 220?
From what I understand, if im probing incorrectly 220VAC (im not sure how is correct or incorrect) nothing happens to the oscilloscope itself. Only the probe wire is blown off, and with a big "scary" bang. Again, im not doing anything to the 220 with my oscilloscope. Just asking.
I know from the tutorials that x10 probe is actually 10 times lower. Thats it. But until 10x probe, lets focus on this 1x probe i have now and what to measure with it.
What is the difference between a DMM and an osciloscope. I mean, I am thinking on an osciloscope as an DMM. And I know is wrong. Tell me what you think I should perceive it, or think it does, or is good for. Especially for you. How YOU perceive it? How You think this tool is good at, when do you think of it? In what circumstances? Thats really on my mind. I hope you get me. I understand its a time measuring device, measuring voltage over time. But I seriously dont make a too much diference from the DMM yet. Or maybe is my total inexperience talking right now, and in time I will figure it out.... But a good analogy/ comparation /guidance/ personal view, will immensely help me.
Like... why should I keep the distance from 220? And especially now that I have everything grounded ?
 

Thread Starter

q12x

Joined Sep 25, 2015
609
For now, stay away from 220VAC. We want you to stay around a bit longer.

Wire up a 555-timer oscillator circuit on your breadboard and use the DSO138 to analyze the circuit by looking at the square wave output on pin-3 and the control signal on pin-6.
I will start your circuit now!
The same question to you as well as I asked mister @dl324 :
" What is the difference between a DMM and an osciloscope. I mean, I am thinking on an osciloscope as an DMM. And I know is wrong. Tell me what you think I should perceive it, or think it does, or is good for. Especially for you. How YOU perceive it? How You think this tool is good at, when do you think of it? In what circumstances? Thats really on my mind. I hope you get me. I understand its a time measuring device, measuring voltage over time. But I seriously dont make a too much diference from the DMM yet. Or maybe is my total inexperience talking right now, and in time I will figure it out.... But a good analogy/ comparation /guidance/ personal view, will immensely help me. "
Like... why should I keep the distance from 220? And especially now that I have everything grounded ?
 

SamR

Joined Mar 19, 2019
3,400
whats the difference
Basically noise reduction. The probe cable is coax which has the ground as the outer sheath. Learn where to and not to connect the ground lead! Big advantage to me is the minigrabber tip which is easier when connecting.
 
Top