(Topic ID: 312644)

Fun with oscilloscopes

By oldschoolbob

2 years ago


Topic Heartbeat

Topic Stats

You

Linked Games

No games have been linked to this topic.

    Topic Gallery

    View topic image gallery

    dso_01_01_00_17_58a (resized).png
    dso_01_01_00_17_29a (resized).png
    dso_01_01_00_16_48a (resized).png
    dso_01_01_00_16_14a (resized).png
    pasted_image (resized).png
    pasted_image (resized).png
    dso_01_01_00_03_19 (resized).png
    dso_01_01_00_03_52 (resized).png
    dso_01_01_00_11_15a (resized).png
    dso_01_01_00_09_38a (resized).png
    dso_01_01_00_09_18a (resized).png
    IMG_8555 (resized).JPG
    IMG_8554 (resized).JPG
    dso_01_01_00_15_05 (resized).jpg
    dso_01_01_00_23_04 (resized).jpg
    pasted_image (resized).png

    #1 2 years ago

    First let me say I know very little about oscilloscopes but I find them fascinating. I love learning about them. A couple of years ago I was having problems with a MPU board. I was told to make sure the 5 volts was stable before the 5 volts shows up on the CPU. (See this thread: https://pinside.com/pinball/forum/topic/mpu-100-don-t-boot-on-first-try/page/2 )

    I did this by attaching probe 1 to R139 and probe 2 to TP5. After several attempts I got what we were looking for. Since learning this I’ve used it several times and it’s been very useful.

    Now I have a new oscilloscope (I couldn’t pass up a bargain). The following scans are from the old scope (Hantek DSO5072P) and the new scope (Hantek DSO2D15). Same MPU, same probes, same method, different scopes. I’m using the “single sequence” that is supposed to capture the moment the signal starts. The old scope catches the signal fine but the new scope seems to miss the very beginning of the channel 2 – it starts at 5 volts.

    I’m sure I’m doing something wrong but I don’t know what. Anyone have a clue?

    pic_67_1 (resized).jpgpic_67_1 (resized).jpg

    dso_01_01_00_05_06 (resized).jpgdso_01_01_00_05_06 (resized).jpg
    #2 2 years ago

    lower your channel 1 trigger on scope 2 to set your zero time to earlier in the signal, or trigger on channel 2 going high

    #3 2 years ago

    It looks like it's partly a trigger issue, like Noahs_Arcade mentioned. I think your trigger is about 2V on the new scope, almost zero on the old.

    Just as important (if not more), the time base is 4mS/Div on the upper trace, 2uS/Div on the lower. This means you essentially zoomed in here a ton more on the new scope:
    pasted_image (resized).pngpasted_image (resized).png

    Nice new toy Bob!

    #4 2 years ago

    First I adjusted the trigger to almost 0 but I think I set it too low and got garbage on the first scan.

    dso_01_01_00_13_36 (resized).jpgdso_01_01_00_13_36 (resized).jpg

    Then I set the time base closer to 4mS. That’s what I was looking for! What I don’t understand is why would the time base make a difference if it’s supposed to trigger on the first sign of a signal. Would the time base be cutting off the first portion of the signal? Why?

    dso_01_01_00_23_04 (resized).jpgdso_01_01_00_23_04 (resized).jpgdso_01_01_00_27_51 (resized).jpgdso_01_01_00_27_51 (resized).jpg
    #5 2 years ago

    I think this is what your asking about:

    Digital scopes have memory - but only so much. And the sampling rate and memory determines how much of the waveform it can capture. If you're at a long time base (i.e. mS), the memory might be getting filled up and you lose data or the data resolution is less (not sure how the scope handles it). I can explain more, but here's a link/SnipIt that does a way better job than what I would type.

    From here: https://www.picotech.com/library/application-note/oscilloscope-tutorial
    pasted_image (resized).pngpasted_image (resized).png

    pasted_image (resized).pngpasted_image (resized).png

    So while digital scopes are fantastic (and inexpensive for home use) they are really a different beast than an analog scope.

    #6 2 years ago
    Quoted from oldschoolbob:

    ...What I don’t understand is why would the time base make a difference if it’s supposed to trigger on the first sign of a signal. Would the time base be cutting off the first portion of the signal? Why?
    [quoted image][quoted image]

    I reread your question above and I think I understand it better now. What you're asking is "Why don't I see the waveform in the area highlighted below?" Correct?

    pasted_image (resized).pngpasted_image (resized).png

    Most digital scopes you can set essentially see a negative offset to trigger (pre-trigger). i.e. Trigger at 2V, but also show 1mS prior. Any chance you changed the time base setting AFTER you captured your sweep. If so, I'm guessing that effects how much 'prior' data was captured. All depends on how it's implemented in the scope, and how much memory is available (relates to my post above).

    #7 2 years ago

    My old scope has 40k memory depth – the new one has 8m. I’d think it should capture a whole lot more. My guess is when I set the time base too short it only picks up a small amount of the scan. (shown in red). But why didn’t it pick up the first of the scan? (shown in orange). I guess the lesson here is not to close in too much on the time base in the beginning, capture more of the scan, then zoom in if required.

    This stuff is so interesting. One could spend years just learning about an oscilloscope. I wish I would have started a long time ago.

    dso_01_01_00_23_04a (resized).jpgdso_01_01_00_23_04a (resized).jpg
    #8 2 years ago

    I don't think Hantek went backwards on the DSO2D15 vs. the DSO5072P. I think it's more likely understanding the best setting for the time base and the sample rate/memory depth w/respect to what you want to measure. It is an inexpensive scope (but very capable) after all.

    Looking at the plot below (using the Hantek manual for clarification), I think you are at 4K storage depth. But your are only seeing pertinent data over 10mS vs. a 50mS sweep. Is the scope set to full bandwidth?

    I'll be the first to admit, I'm not a scope expert - but have a fair amount of experience. But not sure what Hantek uses to determine the 4K storage depth.
    pasted_image (resized).pngpasted_image (resized).png

    1 week later
    #9 1 year ago

    Hey Bob,

    I was watching a video on the DSO02D10 scope. You can adjust the memory depth of the capture.

    Go to to the 17:32 mark in the video.

    The setting is in the Acquire menu
    pasted_image (resized).pngpasted_image (resized).png

    #10 1 year ago

    Thanks Mark, changing the memory depth was easier than I thought. I changed from 4kpt to 4mpt. It gives me more detail but way more than I need for my uses at this time. This is something to keep in my notes for future use. I thought I saw somewhere that 4m would only work with a single channel – two channels would only go to 2m. This screen shot shows both channels and still at 4mpt. That’s pretty impressive for a cheap scope. The more I mess with this scope the more I learn – not just this scope but learning scopes in general.

    dso_01_01_00_23_04 (resized).jpgdso_01_01_00_23_04 (resized).jpg

    dso_01_01_00_15_05 (resized).jpgdso_01_01_00_15_05 (resized).jpg

    Sometime ago you suggested a clamp meter for the scope. I got the CC65 – I think it’s the same as yours. The instructions are useless and I can’t find much on-line about how to use it. If you have time, are you giving free lesions? I did get it to work once but what I saw on the screen didn’t tell my anything I could understand. I tried it again tonight and didn’t get anything. I was trying to read the amps going to this MPU from my power supply we built a long time ago. I have no clue how to use this thing or how to read the information.

    Thanks
    Bob

    IMG_8554 (resized).JPGIMG_8554 (resized).JPGIMG_8555 (resized).JPGIMG_8555 (resized).JPG
    #11 1 year ago
    Quoted from oldschoolbob:

    Thanks Mark, changing the memory depth was easier than I thought. I changed from 4kpt to 4mpt. It gives me more detail but way more than I need for my uses at this time. This is something to keep in my notes for future use. I thought I saw somewhere that 4m would only work with a single channel – two channels would only go to 2m. This screen shot shows both channels and still at 4mpt. That’s pretty impressive for a cheap scope. The more I mess with this scope the more I learn – not just this scope but learning scopes in general.
    [quoted image]
    [quoted image]
    Sometime ago you suggested a clamp meter for the scope. I got the CC65 – I think it’s the same as yours. The instructions are useless and I can’t find much on-line about how to use it. If you have time, are you giving free lesions? I did get it to work once but what I saw on the screen didn’t tell my anything I could understand. I tried it again tonight and didn’t get anything. I was trying to read the amps going to this MPU from my power supply we built a long time ago. I have no clue how to use this thing or how to read the information.
    Thanks
    Bob[quoted image][quoted image]

    Yes, I have the CC65. Is your battery in it dead (i.e. was the green light on?)? Make sure your scope is set to DC coupling and the scope's probe setting to x1. Zero the clamp by not clamping it around anything and press the CC65 button to zero. Then clamp over the wire to measure current. Keep in mind if the current draw is constant - you'll just get a straight line. Also remember the probe only goes to 20KHz, so you may miss some of the faster transitions (if that's what your interested in looking at).

    Once you can see some sort of current, then post again and we can go from there.

    #12 1 year ago

    Zooming in on your picture, you're at 1mV=10mA and 1V/div on the scope. You may need to lower the V/div setting on the scope to see something.

    You power supply is at 280mA. So if everything is set up right, you should measure 28mV (1mv x 280mA/10mA). Pretty hard to see at 1V/div.

    #13 1 year ago

    Thanks Mark, I did have the probe on but the power LED is very dim. DC coupling - OK Probe setting X1 - OK. My problem was the volts/Division - set way too high. I re-set to 10mV and now I get something to see.

    This scan is nothing in the probe loop.

    dso_01_01_00_09_18a (resized).pngdso_01_01_00_09_18a (resized).png

    Next scan is on the 12V line

    dso_01_01_00_09_38a (resized).pngdso_01_01_00_09_38a (resized).png

    Next is the 5V line

    dso_01_01_00_11_15a (resized).pngdso_01_01_00_11_15a (resized).png

    I think it's working but I was expecting it to show amps. If the Vamp is what I see, then why is it showing Vamp = 2.4mV with nothing connected?

    #14 1 year ago

    The 2.4mV is just noise. It's only 24mA and it doesn't appear to be a flat 2.4mV - just residual junk. The average is only 236uV which is really good. Your Vavg is 29mV (290mA) on the 5V line. Is that the correct current?

    The CC65 is pretty low cost and I recall seeing the insides of the CC65 - it's really just analog. Very nice for the money tho (but I wish it had a lot more bandwidth). And 24mA is rather small given the high end (65 amps) that it can measure. You could use averaging on the scope, but then you might miss a transient.

    Looking at the CC65 specs, Hantek say 20mA min. So I think you're actually in good shape. I don't think there's even another low cost option out there - I've looked more than once. Seems you go from this to thousands of dollars (Keysight, Tek).

    Your other option is to use a current sense resistor (very low value) in-line w/the supply voltage. Using the scope, measure the voltage difference across the resistor and divide by the resistance for current. Ch1 on one side of the R, Ch2 on the other side, then subtract the two for the voltage across the R. The scope can automatically calculate the difference between the channels. One nice thing is you're only limited by the scopes BW then and any high freq transients are not lost. But now it's more of a hassle than just clamping on a wire. With high current, you'll drop a little voltage across the resistor. The current sense resistors can be in the milli-ohm range.

    You'd need a smart current probe which changes the display number to A instead of V. I use to use a high speed TeK current probe when I was working that would talk to the a Tek scope and display A, but that entire combo was well north of $10K.

    So how does your current measurements compare to using a DVM?

    #15 1 year ago

    What I don’t understand is where you’re seeing this information. All I see is peak to peak = 4mV, average = 8.71mV and Vamp = 2.4mV. Where does it say how many amps? I guess the information is there but I don’t understand it. And then it has a measurement button that gives even more info. INFORMATION OVERLOAD!!! I have no clue what all that’s telling me.

    dso_01_01_00_03_52 (resized).pngdso_01_01_00_03_52 (resized).png

    dso_01_01_00_03_19 (resized).pngdso_01_01_00_03_19 (resized).png

    You guys that understand electronics amaze me.

    I haven’t used a DMM to measure the amps. If you recall when we built this power supply we couldn’t get separate amp meters to work on both 5 volts and 12 volts. So the amp meter on the power supply shows the amps for both 5 volts and 12 volts combined. It’s showing .28 amps for both. What I’d like to know is the amp draw for the 5 volt line and the 12 volt line.

    I know this oscilloscope is much smarter than me so why doesn’t it just have a button to tell me the amps? It seems to tell me everything else.

    Thanks for the help. Believe it or not, I am learning something.

    #16 1 year ago

    The current probe spits out 1mV for every 10mA. The scope measured 29.14mV. So 10mA x 29.14 (mV) = 291.4 mA
    pasted_image (resized).pngpasted_image (resized).png

    #17 1 year ago

    With the probe zero'd and no wire thru it, it reads 236uV, or 0.236mV 10mA x 0.236 = 2.36mA. Ideally it would be 0V, meaning 0mA. 236uV is very good if you ask me for a $50 current probe!

    The 2.4mV (I probably should have use 2.8mV) is just the pk-pk noise coming out of the probe (remember, it's not measuring a current yet). Ideally the probe would have 0V of residual noise. So 10mA x 2.8 = 28mA in just the junk coming out of the probe. This also includes any noise in the scope, picking up crap in the air, etc. So what this means is if you want to measure current in the 20mA-ish range, it will be hard since the setup noise contributes to any measurement. You can average, that maybe clean up the noise, but you may miss a transient. You average is 236uV with 2.8mV of pk-pk noise riding on it.

    Doing the mV to mA conversions can be error prone since the scope has some manual settings (X1 probe, x10 probe). If you mess those things up, you'll have a wrong reading. More expense scopes/probes do all the conversion since the probes have dedicated probes (with additional connections) that plug into a scope, and the scope display automatically changes from V to A, making it easy to read.

    pasted_image (resized).pngpasted_image (resized).png

    #18 1 year ago
    Quoted from oldschoolbob:

    ... It’s showing .28 amps for both. What I’d like to know is the amp draw for the 5 volt line and the 12 volt line...

    Just measure the 5V and 12V separately, convert to mA.

    You can also place BOTH the 12V and the 5V wire thru the current probe (making sure the current direction is the same) - that's the total current. Should be the same as the meter. Some exceptions to that, but should be OK for this.

    Want a simple trick to read lower currents? Just wrap the wire thru the current probe multiple times (keeping current direction the same). If you wrapped it 3 times around - the reading would be 3X higher (i.e. 1 A in a wire, wrapped 3x would read 3A). Then divided by the number of wraps for the current in the single wire (3A /3 = 1A).

    #19 1 year ago
    Quoted from mbwalker:

    The current probe spits out 1mV for every 10mA.

    That’s the formula I was needing. Now I think I understand how to read the amps.
    The zero’d reading varies a lot. All the Avg readings fluctuate making it a little difficult to see the numbers to the right of the decimal point. But at least I can get in the ballpark. And if I’m within one one-hunderth of an amp – that’s close enough for me.
    I didn’t know about putting both leads in the probe. That’s really interesting. Tonight I did more tests and I think I’m getting the hang of it.

    First scan is nothing in the probe:

    dso_01_01_00_16_14a (resized).pngdso_01_01_00_16_14a (resized).png

    Next scan is the 12 volt line:

    dso_01_01_00_16_48a (resized).pngdso_01_01_00_16_48a (resized).png
    0.0556 amp

    Next is the 5 volt line:
    dso_01_01_00_17_29a (resized).pngdso_01_01_00_17_29a (resized).png

    0.3093 amp

    I’m surprised the 5 volt pulls more amps than the 12 volt.

    Last scan is both 5 and 12 volt lines.

    dso_01_01_00_17_58a (resized).pngdso_01_01_00_17_58a (resized).png
    0.3736 amp
    The meter on the power supply shows 0.29 amp for both 12 and 5 volts. Off by 0.08 amps but close enough.

    I think I learned something this week. Who says you can’t teach an old dog. Now that I know how to use this thing I can see it being very useful. Thanks for suggesting this probe and teaching me.

    Reply

    Wanna join the discussion? Please sign in to reply to this topic.

    Hey there! Welcome to Pinside!

    Donate to Pinside

    Great to see you're enjoying Pinside! Did you know Pinside is able to run without any 3rd-party banners or ads, thanks to the support from our visitors? Please consider a donation to Pinside and get anext to your username to show for it! Or better yet, subscribe to Pinside+!


    This page was printed from https://pinside.com/pinball/forum/topic/fun-with-oscilloscopes and we tried optimising it for printing. Some page elements may have been deliberately hidden.

    Scan the QR code on the left to jump to the URL this document was printed from.