What oscilloscope specs do I need for Arduino projects?

[rstofer]

There are two features of the modern DSO that you just can't get with a CRO and they are terribly important plus the issue of 2 vs 4 channels.

• Decodng:  This can be done with a logic analyzer but it's much more useful to do it with a scope.  You get to see the actual timing of chip select versus clock and things like that.
• The big deal is single shot trigger mode. This mode captures a trace for one  sweep (one buffer full, 1/2 buffer before the trigger and 1/2 after the trigger) and holds it forever.  You can set the trigger point to be anywhere on the screen, not just in the center.  There are analog storage scopes but they don't work nearly as well as the modern DSO in terms of single shot mode.  In my view, this is the most important feature of the modern DSO
• There is also the 4 channel business.  Better to have them and not need them than the other way around.  There are 4 channel analog scopes and if you go that way, try to concentrate on those with 4 channels
  

I see nothing to gain by buying an obsolete CRO and then turning around in a year or so and buying a DSO.  Mind you, I still have my Tek 485 but it's been around for at least 12 years and the DS1054Z for just a couple.

For the very beginner with nothing on their bench, I would highly recommend the Digilent Analog Discovery 2.  Two channel scope, two channel arbitrary waveform generator, dual power supply and 16 digital pins that can be used as a logic analyzer.

https://store.digilentinc.com/analog-discovery-2-100msps-usb-oscilloscope-logic-analyzer-and-variable-power-supply/

I know it doesn't have a 4 channel scope and that's regrettable but what it does have is simply spectacular for breadboarding.

[Dubbie]

In my teens I designed and built my first computer (based on a 6800, 128bytes RAM, TTL, switches, LEDs and home-etched PCBs) with only a multimeter.

I don’t doubt that in the slightest. However with that sort of digital project you can single step through the logic, checking that the state is as you would expect literally step by step.

Imagine a microcontroller project with tight timing requirements and many tasks interacting. How on earth do you figure out where there is a hardware problem or software issue? Plugging in a scope might reveal in 10 seconds that you made an error configuring your DMA, or that your wiring is not up to scratch for the bus speed you are running. something that might take hours or poring through code or messing with hardware to discover otherwise.

[tggzzz]

In my teens I designed and built my first computer (based on a 6800, 128bytes RAM, TTL, switches, LEDs and home-etched PCBs) with only a multimeter.

I don’t doubt that in the slightest. However with that sort of digital project you can single step through the logic, checking that the state is as you would expect literally step by step.

Only partially true. The technique is to test each part of the system (hardware, software, compiler, application) in isolation before interconnecting them. Only the final test requires full-speed operation.

That strategy is necessary for all complex systems, both hardware and software.

Imagine a microcontroller project with tight timing requirements and many tasks interacting. How on earth do you figure out where there is a hardware problem or software issue? Plugging in a scope might reveal in 10 seconds that you made an error configuring your DMA, or that your wiring is not up to scratch for the bus speed you are running. something that might take hours or poring through code or messing with hardware to discover otherwise.

I don't have to imagine that! I am very well acquainted with all those concepts, problems, and the range of techniques and solutions.

Only a scope can measure and detect the "signal integrity" issues you mention. But a beginner won't know what to look for, nor know how poor probing technique will produce misleadingly invalid results.

A scope won't help solve tight timing requirements and task interaction. Printfs and simple cheap logic analysers are sufficient (drive an output high/low at appropriate points in the code). Even a multimeter or LED can be a useful diagnostic technique, e.g. an average voltage can be related to average timings.

A scope won't be any extra help w.r.t. setting up DMA correctly.

Nonetheless, a scope can be used and be helpful - and can distract and mislead!

[rstofer]

A scope won't be any extra help w.r.t. setting up DMA correctly.

Trigger on DMA Request and watch for DMA Grant.  Clearly, this can be done with a logic analyzer but it's not clear to me that the cheapest LAs can resolve much better than 10 ns and that's a lifetime in logic terms.  Unless, of course, the LA is using an external state clock.  An LA without a state clock input is mostly useless.

I think a scope if the better tool for checking setup and hold times even though a 100 MHz scope probably has a rise time of 3.5 ns.  The data and clock signals have the same rise time so their relationship is still easy to understand.

If you want to review a single I2C or SPI transaction, the 4 channel scope is handy because it will also be looking at signal integrity.  If you want to decode "War and Peace", a logic analyzer is a better choice.

In the end, people wind up with both tools.

[tggzzz]

A scope won't be any extra help w.r.t. setting up DMA correctly.

Trigger on DMA Request and watch for DMA Grant.  Clearly, this can be done with a logic analyzer but it's not clear to me that the cheapest LAs can resolve much better than 10 ns and that's a lifetime in logic terms.  Unless, of course, the LA is using an external state clock.  An LA without a state clock input is mostly useless.

That's one of the issues I have against cheap LAs. Expensive LAs finesse the issue by the expense of halving the sample rate and constraining the allowable "clock" width. Vintage LAs did it properly, but slowly!

I think a scope if the better tool for checking setup and hold times even though a 100 MHz scope probably has a rise time of 3.5 ns.  The data and clock signals have the same rise time so their relationship is still easy to understand.

Completely agreed. Scopes are the weapon of choice for signal integrity issues.

If you want to review a single I2C or SPI transaction, the 4 channel scope is handy because it will also be looking at signal integrity.  If you want to decode "War and Peace", a logic analyzer is a better choice.

A decent LA will allow you to skip the boring bits of War and Peace, and only read the key scenes A scope can't do that.

In the end, people wind up with both tools.

Yes, but there is a lot of overlap where it is possible to use either. It is fruitful to understand where one tool cannot be used and the other must be used - i.e. a tools USP

[rstofer]

Yes, there's overlap but, in my view, the scope is useful in a broader area.  Mostly, we're talking digital in this thread but that a limited view of electronics.

I like analog computing, I need some kind of scope to see the analog output.  It doesn't need whiz-bang specs because the time constant for integration is still one second but it does need dual channels and x-y mode.

To Arduino projects, almost everything will be digital but if I could only have a scope OR a logic analyzer, I'm pretty sure I would start with the scope.

Rigol DS1054Z unlocked to 100 MHz  -- what I am using today and it works well
Siglent SDS1104X-E unlocked to 200 MHz -- what I plan to get someday

[rstofer]

As long as we're talking ATmega328P Arduinos, bandwidth isn't such a big deal.  50 MHz and up should cover it.

However, it is worth noting that the Teensy 4.1 uses the Arduino infrastructure and matching libraries.  Application code is mostly portable and it runs at 600 MHz!  I'm not sure of the details but apparently it can toggle pins at 100 MHz. That's blistering fast!

[wizard69]

...snipped

Now, over to the traditional set of comments that analogue scopes should be avoided like the plague...

Ive read a few of those comments and don't believe them for a minute.    A functional scope as you point out is important but there is valuable learning with analog scopes.   I'm not knocking digital scopes just that for a few bucks you can get a good grounding in viewing wave forms.   As you note you need to learn to probe and learn and understand what the host of knobs do.

Knocking analog scopes is kinda like knocking analog VTVM that where the staple of the industry for decades.   The accuracy might not be there but that doesn't imply that they are not useful.   

[tggzzz]

As long as we're talking ATmega328P Arduinos, bandwidth isn't such a big deal.  50 MHz and up should cover it.

What's the risetime? For a scope's USP the clock rate is irrelevant, as I'm sure you are well aware.

What's the risetime of whatever is connected to the arduino, especially transients related to switching currents fast?

However, it is worth noting that the Teensy 4.1 uses the Arduino infrastructure and matching libraries.  Application code is mostly portable and it runs at 600 MHz!  I'm not sure of the details but apparently it can toggle pins at 100 MHz. That's blistering fast!

I've an MCU that will do arbitrary input/output at up to 250Mb/s on many i/o ports simultaneously. It will also count the transistions on one or more 62.5Mb/s input streams, plus do front- panel i/o plus communicate over a USB link to a PC - all at the same time. Now that's blisteringly fast

[james_s]

What's the risetime? For a scope's USP the clock rate is irrelevant, as I'm sure you are well aware.

What's the risetime of whatever is connected to the arduino, especially transients related to switching currents fast?

For a ATMEGA328P based Arduino I measured the rise and fall times for IO pins a while back at around 5ns.

In practice I can't say I've ever really needed to know that though, it was just out of curiosity. I don't normally care what the rise time is, it's negligible compared to the dwell times and when I'm looking at the signal in or out of a microcontroller I usually just want to know if the pin is toggling, if the levels look reasonable, and then does it look like the pattern that I expect to be there. It's not important that the scope might not show all the fine details, if I really need to see that I've got a 1GHz scope on the bench but most of the time for this stuff I'm just going to use the little one with 100MHz probes, good enough.

There are niche cases where it matters, but for the typical hobbyist using something like an arduino the rise time is largely irrelevant, it is what it is, if you have the budget for an exotic scope you probably won't be using an arduino in the first place. More bandwidth is a nice luxury but it's ridiculous and elitist to suggest that one cannot get by without it when so many do.

[tggzzz]

What's the risetime? For a scope's USP the clock rate is irrelevant, as I'm sure you are well aware.

What's the risetime of whatever is connected to the arduino, especially transients related to switching currents fast?

For a ATMEGA328P based Arduino I measured the rise and fall times for IO pins a while back at around 5ns.

In practice I can't say I've ever really needed to know that though, it was just out of curiosity. I don't normally care what the rise time is, it's negligible compared to the dwell times and when I'm looking at the signal in or out of a microcontroller I usually just want to know if the pin is toggling, if the levels look reasonable, and then does it look like the pattern that I expect to be there. It's not important that the scope might not show all the fine details, if I really need to see that I've got a 1GHz scope on the bench but most of the time for this stuff I'm just going to use the little one with 100MHz probes, good enough.

There are niche cases where it matters, but for the typical hobbyist using something like an arduino the rise time is largely irrelevant, it is what it is, if you have the budget for an exotic scope you probably won't be using an arduino in the first place. More bandwidth is a nice luxury but it's ridiculous and elitist to suggest that one cannot get by without it when so many do.

The key point is knowing the theory, so people can predict where it does matter.

I repeatedly point out that, with skill imagination and thought, you can debug a hell of a lot with a multimeter, LEDs, and printf statements. One classic example is using a voltmeter to measure an MCU's average percentage idle time.

[Ian.M]

If you are on a very limited budget, you *DON'T* need that 100MHz 4 channel DSO.   Even a 50MHz dual channel CRO (in good condition) + a USB logic analyser + a cheap DMM is sufficient for hardware debugging of nearly all AVR based Arduino (and other 8 bit MCU) projects, including checking for most signal integrity issues.   Of course I'd prefer a 100MHz delay timebase CRO, but not if it was going to cost me big bucks that I should be saving towards getting a good modern DSO when I actually need one. 

OTOH good CROs are getting harder to find in good condition, and a late CRO era analog scope that needs significant repairs is a mill-stone around the neck of a novice who doesn't have the budget, experience and test equipment to restore it to good working order.  I wouldn't even consider a faulty CRT era DSO or MSO.

Most cheap off-brand handheld scopes and cheap low-end USB scopes are essentially worthless for anything much above audio and ultrasonic frequencies, and the software/firmware is often a reeking pile of sh!te that would fail any independent real world usability testing!  Don't get one unless you need extreme portability, literally a lab in a briefcase

[james_s]

I'll always have a soft spot for analog CROs, but IMO the only reason a hobbyist should consider one is if it's very cheap and budget doesn't allow one of the hobbyist oriented "real" DSOs that you can get for ~$350-$400. There is still value in playing with an analog scope but beyond XY mode they don't offer anything over even a low end DSO. I love my Tek 465B and don't plan to get rid of it but I very rarely use it once I got a decent DSO. A nice older analog scope is better than the toy DSOs but outside of a few niche applications digital is superior.

[tggzzz]

I'll always have a soft spot for analog CROs, but IMO the only reason a hobbyist should consider one is if it's very cheap and budget doesn't allow one of the hobbyist oriented "real" DSOs that you can get for ~$350-$400. There is still value in playing with an analog scope but beyond XY mode they don't offer anything over even a low end DSO. I love my Tek 465B and don't plan to get rid of it but I very rarely use it once I got a decent DSO. A nice older analog scope is better than the toy DSOs but outside of a few niche applications digital is superior.

Given the choice between a working analogue scope from 70s-90s and a digitising scope older than a decade, I would probably choose the analogue scope.

Earlier digitising scope were just too limited for many purposes. Examples... They couldn't show the peak and mean values in a display sample. The number of samples was too short to be able to zoom in on relevant features occurring long after the trigger.

Apart from that, I have a couple of digitising scopes that I use on the few occasions when their USP is valuable (single shot, postprocessing, raw bandwidth). But for the responsiveness, simplicity and ease of use I keep an old analogue scope on my bench. Those emphasised points are important for a beginner.

[Dubbie]

To be honest, I don’t know why people make out oscilloscopes to be this hard to use thing. Once you get the general concept, you can generally feel your way around an unfamiliar one in very short order. It’s the rest of being a good EE that is the hard part! Not using a scope! I don’t think it matters about learning a CRO first then working your way up to a DSO. It’s not rocket science. Start with whatever is most convenient to get your hands on and you will be completely fine I guarantee it. Now if only designing robust and well performing circuits was as easy! 

[tggzzz]

To be honest, I don’t know why people make out oscilloscopes to be this hard to use thing. Once you get the general concept, you can generally feel your way around an unfamiliar one in very short order. It’s the rest of being a good EE that is the hard part! Not using a scope! I don’t think it matters about learning a CRO first then working your way up to a DSO. It’s not rocket science. Start with whatever is most convenient to get your hands on and you will be completely fine I guarantee it. Now if only designing robust and well performing circuits was as easy! 

CRO vs DSO indicates you are confused, which may be significant. CROscilloscope is an output technology, DSOscilloscope is an input and processing technology. I have a LeCroy digitising (and digital) scope that has a cathode ray output.

Note that the context is that the OP is a beginner.

Of course, everything can be learned especially once you have the fundamentals under your belt. Nonetheless, having everything visible on the front panel does make it simpler.

Even experienced professionals are misled and frustrated by subtle important settings hidden three deep in a menuing system. Typical expressions I've repeatedly heard include "I don't believe that" and "what's it doing now".

[RoGeorge]

Since there is no budget limit in the OP, buy the best available one, a Keysight UXR 110GHz BW, 256GS/s, 10-bit Real-Time Oscilloscope



 

[Mr. Scram]

CRO vs DSO indicates you are confused, which may be significant. CROscilloscope is an output technology, DSOscilloscope is an input and processing technology. I have a LeCroy digitising (and digital) scope that has a cathode ray output.

Note that the context is that the OP is a beginner.

Of course, everything can be learned especially once you have the fundamentals under your belt. Nonetheless, having everything visible on the front panel does make it simpler.

Even experienced professionals are misled and frustrated by subtle important settings hidden three deep in a menuing system. Typical expressions I've repeatedly heard include "I don't believe that" and "what's it doing now".

I don't think anyone is confused about what he's saying. CRO is often used as analogue for analog on here. Digital or analogue doesn't matter much. Don't get fooled into a quest to find an analog oscilloscope if a decent digital one presents itself. The reverse is also true. Getting started isn't rocket science either way. I suspect much of the frustration of experienced professionals stems from them growing up with different technology, while younger people take to menu based systems without issue.

[Ian.M]

CRO vs DSO indicates you are confused, which may be significant. CROscilloscope is an output technology, DSOscilloscope is an input and processing technology. I have a LeCroy digitising (and digital) scope that has a cathode ray output.

Note that the context is that the OP is a beginner.

Errr  . . . *NO*.   A CRO is analog all the way from the input or ext trigger BNCs to the CRT deflection plates.  There may^* or may not be some digital readouts for attenuator and timebase settings and maybe even an integrated DMM.  A DSO digitises its inputs (after some analog preprocessing) and has a digital counter timebase.  its display technology is (mostly^#) irrelevant.   A MSO is a combo of a CRT DSO and a CRO on the same CRT.

* As  CROs are ageing beasts, 'pure' CROs without digital 'encrustations' are vastly preferable as they are simpler and thus more maintainable.

# The display technology may influence the display update rate.

Of course, everything can be learned especially once you have the fundamentals under your belt. Nonetheless, having everything visible on the front panel does make it simpler.

Even experienced professionals are misled and frustrated by subtle important settings hidden three deep in a menuing system. Typical expressions I've repeatedly heard include "I don't believe that" and "what's it doing now".

Too true.  If you have enough experience with scopes, and not just a few semesters setting them strictly according to the lab guide for your course, even if you are a hobbyist who gained that experience using a decent CRO as your 'daily driver', you'll have a good idea when a DSO is telling you porkies, know when to dig into the menus and wont be so dependent on its 'autosetup' button.  However that still takes time and a brain firing on all cylinders, so many of us here miss the easy days when all you had to do to get sanity out of a CRO was to push in all pullout knobs, set shift controls to mid-range and everything else to 'cal', and select appropriate input coupling, attenuator, trigger and timebase settings.

@RoGeorge: I doubt I could even afford a day's rental on that beast!

[Wallace Gasiewicz]

OK, this is from someone who has been using old scopes for a while and has not used Arduino technology. (perhaps I should get Arduino for Idiots) I am expecting my second DSO any day now(Agilent 54810A), I sold an old digital scope years ago, I did not think the older digital scopes were competitive with a good analog. I use scopes to fix old stuff. I use a HP 1980 scope system at present and have a Tek 475 also. The 1980 has some digital features but essentially is an analog scope. It also has digital display memory but that is another story.
What frequencies are we talking about with the Arduino? What voltage levels are common digital signals?
I know that I do not know.
It is very difficult to see a non repeating signal on an analog scope. You have to get the circuit to "repeat" to have a decent chance of seeing the signal. Trouble shooting such things as trigger circuits takes a lot of time.
I would think that one shot would help a lot.
Since with an Arduino we are dealing with several digital signals would not a logic analyzer be more helpful? Some old ones are cheap but I do not know if they meet the freq needs etc (that's why I asked about freq requirements)...I sold a HP logic analyzer that was a 200 MHz scope for $100, working, with leads. I hated the display however. Again I do not know what freq we are talking about with the Arduino. If frequency is low enough, maybe one of these old logic analyzers would be the most efficient use of financial resources. A logic analyzer and a 200 MHx scope for $100, And a great huge box. HA! What do you folks think?
On fixing old equipment, it is difficult to connect more than a few probes, it would seem that putting together a fresh Arduino project, it would be far easier to leave access to many signals so you could easily connect a logic analyzer to see many signals in real time.

[tggzzz]

CRO vs DSO indicates you are confused, which may be significant. CROscilloscope is an output technology, DSOscilloscope is an input and processing technology. I have a LeCroy digitising (and digital) scope that has a cathode ray output.

Note that the context is that the OP is a beginner.

Of course, everything can be learned especially once you have the fundamentals under your belt. Nonetheless, having everything visible on the front panel does make it simpler.

Even experienced professionals are misled and frustrated by subtle important settings hidden three deep in a menuing system. Typical expressions I've repeatedly heard include "I don't believe that" and "what's it doing now".

I don't think anyone is confused about what he's saying.

A beginner, such as the OP, looking up the acronyms ought to be confused.

CRO is often used as analogue for analog on here.

You mean "analogue for analogue" And yes, the terms are poorly used here - as are others which measure time in mohs (e.g. 10mS instead of 10ms).

It is all wrong, wrong I tell you, wrong!

Digital or analogue doesn't matter much. Don't get fooled into a quest to find an analog oscilloscope if a decent digital one presents itself. The reverse is also true.

Agreed.

(Unless it is a crap digital scope made by Schlumberger where the user interface was created by softies. The vertical sensitivity was marked "calibration" )

Getting started isn't rocket science either way. I suspect much of the frustration of experienced professionals stems from them growing up with different technology, while younger people take to menu based systems without issue.

I've been using menu systems for 38 years starting on a Sun 1 and continuing on Lisas and Mac. They have never confused me.

The problem is things hidden inside a menu hierarchy, without being very visible at the point of making a measurement.

[tggzzz]

CRO vs DSO indicates you are confused, which may be significant. CROscilloscope is an output technology, DSOscilloscope is an input and processing technology. I have a LeCroy digitising (and digital) scope that has a cathode ray output.

Note that the context is that the OP is a beginner.

Errr  . . . *NO*.   A CRO is analog all the way from the input or ext trigger BNCs to the CRT deflection plates. 

Er, **YES**

A cathode ray oscilloscope (CRO) uses a CRT to display the results. Some of my CROs (e.g. Tek 24x5) are analogue all the way through. Others (e.g. my LeCroy 9310AM) have an analogue front end followed by a digitiser and DSP, and the results are displayed on a pleasant monochrome orange CRT.

Here's a picture of it on auto trigger, to make the time and amplitude samples very visible. Note the 100MS/s above the top right of the CRT:

There may^* or may not be some digital readouts for attenuator and timebase settings and maybe even an integrated DMM.  A DSO digitises its inputs (after some analog preprocessing) and has a digital counter timebase. 

If you believe that, you are wrong. Please explain the picture below of my Tek 2465 scope (ICs have 1984 datecodes) with integral counter timer.

You should take into account that the 24x5s are widely regarded as analogue scopes, from beginning to end.
For the sine wave note the precision of the frequency readout, made by the scope without my setting cursors. (Neither the oscillator nor scope had warmed up; the OCXO is <1ppm)
For the pulses, note that the scope has measured the positive width without my setting cursors.



Amusingly and for the avoidance of doubt, the 2465 counter/timer/word recogniser interface is extremely confusing, even worse than a menu system

its display technology is (mostly^#) irrelevant.   A MSO is a combo of a CRT DSO and a CRO on the same CRT.

Maybe some people think of an MSO that way - but if they wish to have a common language with other people they will have to state their definition at the start of a conversation.

To companies like Keysight a Mixed Signal Oscilloscope (MSO) is something with a few analogue channels and more digital channels. Effectively they are a combination of scope and a simple logic analyser with the same timebase. They can also display multiple digital signals as a single bus, and the like. The first example returned by google: https://www.keysight.com/en/pdx-x201841-pn-MSOX3012A/mixed-signal-oscilloscope-100-mhz-2-analog-plus-16-digital-channels?cc=HU&lc=eng

[tggzzz]

OK, this is from someone who has been using old scopes for a while and has not used Arduino technology. (perhaps I should get Arduino for Idiots) I am expecting my second DSO any day now(Agilent 54810A), I sold an old digital scope years ago, I did not think the older digital scopes were competitive with a good analog. I use scopes to fix old stuff. I use a HP 1980 scope system at present and have a Tek 475 also. The 1980 has some digital features but essentially is an analog scope. It also has digital display memory but that is another story.
What frequencies are we talking about with the Arduino? What voltage levels are common digital signals?

The maximum frequency in the signal is defined by the risetime, not the frequency. The rule of thumb is BW=0.35/t_r. A little theory and a couple of practical measurements are shown here: https://entertaininghacks.wordpress.com/2018/05/08/digital-signal-integrity-and-bandwidth-signals-risetime-is-important-period-is-irrelevant/

I know that I do not know.
It is very difficult to see a non repeating signal on an analog scope. You have to get the circuit to "repeat" to have a decent chance of seeing the signal. Trouble shooting such things as trigger circuits takes a lot of time.
I would think that one shot would help a lot.

Truly one-shot events are the USP for storage scopes, whether digitising storage scopes or analogue storage scopes (may they rest in hell).

Except that a general good principal is to make any situation, either correct operation or buggy operation, repeatable. When that is possible then the storage becomes less valuable.

Since with an Arduino we are dealing with several digital signals would not a logic analyzer be more helpful? Some old ones are cheap but I do not know if they meet the freq needs etc (that's why I asked about freq requirements)...

You can get simple slow (24MS/s/channel??) modern LAs very cheaply. They will be useful for many "Arduino tasks" but certainly not all. If nothing else, they would be a good way to gain experience.

As with all tools, learn to exploit what it can do, and be aware of how it will lie to you

I sold a HP logic analyzer that was a 200 MHz scope for $100, working, with leads. I hated the display however. Again I do not know what freq we are talking about with the Arduino. If frequency is low enough, maybe one of these old logic analyzers would be the most efficient use of financial resources. A logic analyzer and a 200 MHx scope for $100, And a great huge box. HA! What do you folks think?
On fixing old equipment, it is difficult to connect more than a few probes, it would seem that putting together a fresh Arduino project, it would be far easier to leave access to many signals so you could easily connect a logic analyzer to see many signals in real time.

200MS/s per channel would be more than adequate, but make sure the sample depth is sufficiently long.

[Wallace Gasiewicz]

I think I get it, the usefulness of a "scope" in this situation is it's ability to show brief sharp pulses, which are common in computer circuits. I have noticed that one old scope is different from another in it's ability to display a pulse somewhat independent of it's MHz rating
So Perhaps one of the old HP logic analyzers that doubles as a 100-200 MHz scope might be a good choice for the OP.
Might be pretty inexpensive and the OP will also get a usable scope. This might enable further experimentation and descent into TE acquiring habits.

As an aside, My HP 1980 has a digital storage for waveforms that appear on the screen. It takes about 3-4 seconds for it to scan the waveform and then display it as a series of dots. This feature has very limited usefulness. Interesting, but dumb. as compared to today's digital scopes.
Wally

[tggzzz]

I think I get it, the usefulness of a "scope" in this situation is it's ability to show brief sharp pulses, which are common in computer circuits. I have noticed that one old scope is different from another in it's ability to display a pulse somewhat independent of it's MHz rating

All the signals in an Arduino are analogue. However, the receiving logic gates can accurately interpret them as digital signals, if (and only if) they meet the requirements in terms of voltage and timing.

The scopes USP is that it can show you the voltages (>X for a logic 1, <Y for a logic 0) and the relative timings (t_setup and t_hold). For the latter you need two channels at least, and sometimes more is convenient. This is "ensuring signal integrity".

After you have verified signal integrity, you can choose to "flip to the digital domain" and debug digital signals with a logic analyser or printf statements. A logic analyser will have many more inputs than a scope, and can trigger on patterns rather than just voltage levels. It can also ignore "uninteresting" signals, e.g. only record what happens at a clock signal. That can be helpful.

On the other hand, if you look at digital signals with a scope, you can (and sometimes the scope) can interpret the waveforms visually as digital signals.

So, there is overlap between scopes and logic analysers, as well as important differences. Choose a screwdriver for screws, and a hammer for nails

So Perhaps one of the old HP logic analyzers that doubles as a 100-200 MHz scope might be a good choice for the OP.
Might be pretty inexpensive and the OP will also get a usable scope. This might enable further experimentation and descent into TE acquiring habits.

As an aside, My HP 1980 has a digital storage for waveforms that appear on the screen. It takes about 3-4 seconds for it to scan the waveform and then display it as a series of dots. This feature has very limited usefulness. Interesting, but dumb. as compared to today's digital scopes.
Wally

I designed and built my first computer with LEDs and a multimeter. It required care and thought, but that is not a bad thing!

Use the tools you have. When you can't think of a way to use them to see what you need, you will know what you need to obtain.

Simple example. I've just been preparing a Tek 2465DMS scope for fleabay. I had to replace the infamous RIFA capacitors, and then found everything worked except that it wouldn't display current. Now that scope has many advanced (for 1984!) features including a microprocessor, and the problem could have been in many places, digital or analogue. In the end I used a multimeter to find where the signal had not reached, and eventually spotted a wire had separated from an input relay. Resolder it and job done.