I recently decided to buy my first oscilloscope to help with the process of learning more about electronics. The process of selecting an oscilloscope has been longer than expected. I started by looking at the scopes that Sparkfun and Adafruit offered, which lead me to wonder what other options were out there. I was a bit overwhelmed at the variety of models and manufactures, but managed to cut through a lot of the noise.

In this post, I’ll talk more about how I narrowed things down further, and what I ended up choosing.

To start, its worth covering why I wanted an oscilloscope in the first place. It all stems from a growing interest in the declining costs of capable “systems on a chip,” low power communication technologies like Bluetooth LE, and even WiFi, and the accessibility of the Chinese electronics manufacturing supply chain. Taken together, it seemed to me that I should learn enough about electronics to have a sense of the possibilities and limitations, and to be better able to collaborate with people with deeper expertise. This approach served me well in the past when I worked on software projects; I wasn’t a programmer, but I understood enough to be a good collaborator.

In looking around for learning projects, I decided to explore the world of power sources for these devices with a new site called Power Cartel. Part of what I’m doing on Power Cartel is doing teardowns of battery packs and chargers, with the goal of collaboratively creating useful opensource designs. In order to dive deeper in my teardowns, and support my own design efforts, I need to be able to start exploring what is happening inside the circuits and understanding how the different components interact.

There are a lot of test instruments. I already have a basic multimeter, but I felt like I needed a way to look at signals over time. There are two instruments that fit that job description. A data logger or chart recorder is useful for looking at signals over long periods of time (ie hours), where as an oscilloscope is good for looking at signals over much shorter periods, seconds down to micro, or even nanoseconds. I actually want to look at signals over both time periods. I want to look at current and voltage for charging and discharging batteries over the period of hours or days, but I also want to look at sub-second changes in signals.

I decided to start with an oscilloscope, rather than a data logger, because the sub-second changes are more fundamental. With a better understanding of such things, I could build my own data loggers. Moreover, most modern digital storage oscilloscopes can actually record signal changes over longer periods of time, and they can be connected to a computer for control and data recording.

I originally thought that some sort of oscilloscope module that I could connect to my computer or iPad would be a good place to start because it would save me money and space. I quickly learned there were problems with that approach. Most electrical engineers and technicians are trained on traditional stand-alone oscilloscopes, and training aside, traditional stand-alone oscillosopes are often easier/faster to work with because they have dials and buttons arranged in a user interface that has seen steady improvement for close to a century. Connected scopes are newer, and more of a niche item, so their software is less refined. More importantly, because they are a niche item, there is less competition and scale to push prices down, so any savings that might come from omitting a screen and controls is offset. As a result, USB scopes are not any cheaper than stand-alone scopes with otherwise similar specifications. The space savings was still attractive, but I decided I was going to purchase a stand-alone scope.

With that decision made, I had to figure the other key specifications for my work. For any scope, whether an older analog scope, or a more modern digital storage scope, bandwidth is a key consideration. Bandwidth determines the range of signal frequencies you can measure with the scope. Adafruit sells scopes with 50MHz and 100MHz bandwidth. Sparkfun’s stand-alone scope offering is 100MHz. From a little reading, the switch mode power supplies I’m going to be working with typically operate in the range of 200KHz to 2MHz, and the microcontrollers I’m working with operate at 4-16MHz, or perhaps 50-70MHz. Some of the wired communications protocols I’m using may be 5MHz.  It would seem then that a 50-100MHz scope would cover almost anything I’m likely to use it for in the near future.

Closely related to bandwidth is the sampling rate. Sampling rate is the number of times per second a signal is read. For a pure sine wave, an accurate estimate of frequency and amplitude requires a sampling rate that is at least two times higher than that of the signal being measured. One of the big reasons for having an oscilloscope though is to look at signals that are not pure sine waves. A lot of digital communications use square   wave signals, and a lot of signals, whether square, sign, step, pulse, or something else, can get distorted by characteristics of the circuits they travel in. A rule of thumb I’ve come across is that the sample rate should be 4x the frequency of the signal you are observing.

Almost all the scopes in my price-range ($400-650) have a 1GHz max sample rate. That may sound like overkill for a 100MHz scope, but in this segment of the market, that sample rate is across all the channels of the scope. So, if you have a scope with two channels, and you are using both of them, thats a 500MHz rate per channel, which is closer to the rule of thumb.

The next thing I considered was the number of channels. Each signal you measure requires a channel. Often you are comparing two signals against each other some how, and so, not surprisingly, most scopes have at least two channels, and, indeed, in this entry level segment, most don’t have more than two channels. I found a few with four channels, though. Most were out of my price range, but one, the Rigol DS1074Z was available for under $600. A two channel scope would probably do everything I reasonably needed, but the option of having four channels was intriguing. Four channels would allow me to look at voltage and current at the same time for both the input and output of a power supply. Even better, I could use some of the channels as a basic logic analyzer, and look at how analog signals changed in relationship to specific digital signals.

The consideration of the number of channels also turned my attention to scopes with a logic analyzer option to look at even more digital signals. Oscilloscopes with this feature are generally called Mixed Signal Oscilloscopes, which add 8 or 16 logic channels. The added digital channels come with an added cost. There is a $600 mixed-signal scope from Rigol (DS1052D), but it only has two analog channels, 50MHz bandwidth, and 1Mpts of memory. The Rigol MSO10747Z, which is the mixed signal version of the DS1074Z is $250 more expensive, and out of my price range. Since people seemed less bothered by USB logic analyzers, and since a cheap one could be had or $20 or so, I decided that I didn’t need a full logic analyzer.

Another consideration is the amount of memory available to hold samples. The Rigol DS1074Z has memory for twelve million sample points (12Mpts). Some of the alternatives I considered, like the Siglent SDS1102CML only has 2Mpts of memory, and the Siglent SDS1074CFL only has 24Kpts.

By now, you’ve probably figured out the DS1074Z is the scope I’m leaning towards. I took repeated looks at the other options from Rigol and Siglent, but kept coming back to the DS1074Z.

Comparison

Cheaper

• Siglent SDS1072CML for $319: +lower price -2 channels -memory
• Rigol DS1052E for $329 +lower price -50MHz -2ch -smaller screen – older
• Siglent SDS1102CML & SDS1102CNL ~$360 +lower price +100MHz -2ch -smaller memory -can’t tell how they differ from each other, other than memory
• Gatten GA1102CAL $400 +lower price +100MHz -2ch -smaller memory

I would have liked spending less, but I wasn’t willing to go with a last generation Rigol, or forgo 2 channels and a bunch of sample memory just to save $150 or so

Similar

• Siglent SDS1202CNL+ $546 +200MHz, 2Gigasamples/s -2ch -memory
• Rigol DS1052D $610 +16 channel logic analyzer, -2ch -memory

The higher bandwidth and sample rate of the Siglent just didn’t seem that compelling, and nor did spending another $60 for the 16-channel logic analyzer on a last generation instrument.

More Expensive

• Siglent SDS1074CFL $723 -higher price +2GSa/s, =4ch, – memory
• Siglent SDS2072 $805 -higher price, +2GSa/s +memory -2ch +larger screen
• Rigol DS1074Z-S $818 +signal generator
• Rigol DS1104Z $830 +100MHz bandwidth
• Rigol MSO1074Z $835 +16 channel logic analyzer
• Rigol DS2072A $839 -higher price -2ch +2GSa/s

The price was really enough to knock all of these out. The Siglent SDS1074CFL was tempting since it had 4 channels and a higher sample rate, but the higher sample rate isn’t that important to me at this point, and so not worth the extra $175 or so. The only other one I gave serious consideration to was the MSO1074Z, but the integrated logic analyzer just didn’t seem compelling enough to drop another $280 or so.

Finally

In the end, the Rigol DS1074Z won me over with its combination of price, four channels and deep memory, along with the fact that Rigol seems to be a well-understood quantity at this point. This model has been out for almost a year, most of the bugs are known, and many have already been address. There are lots of good in depth reviews and tutorials for Rigol scopes. Certainly more than I saw for Siglent/Atten/Gatten or Owon.

The Rigol has another thing in its favor. It apparently shares the same hardware as the DS1104Z, and people have figured out a way to unlock the higher bandwidth. They’ve also figured out how to unlock some otherwise extra cost after market options, most of which don’t interest me, but its nice to have the option.

I ended up ordering my scope from TEquipment.net, and paid less than $585 with free shipping thanks to a discount they offer members of EEVblog.

Earlier I wrote a long blog post that condensed down the path I’ve taken to buying my first oscilloscope. I hadn’t decided what to buy though., so this post will continue with more of the decision making process.

But first, a short review of the ground I covered in my earlier post. I explained that I needed an oscilloscope to help me better understand why circuits work, or don’t work. I’m not just doing this for fun, my goal is to start designing and building some useful circuits of my own. I covered how I started figuring out what my options were for an entry-level scope, in order to better understand what I should be thinking about.

At the end, I’d concluded that buying a cheap compact oscilloscope like the DSO Quad wasn’t a good idea (not capable enough to be useful for long, and not cheap enough given its limitations), and why a USB scope wasn’t going to save me any money (the meager savings from omitting a screen and controls are offset by the higher prices that come with limited volumes).

I started by considering Rigol scopes like the dual-channel Rigol scopes sold by Adafruit, or the dual-channel. Gratten scope sold by Sparkfun. At this point though, I’ve all but ruled out those options. The truth is, at $390-460, they are all within my budget, and with 50-100MHz of bandwidth, they can all do what I think I’m going to need them to, which is to deal with ~1-2MHz signals from switch mode power supplies. The problem is, while I don’t know much about oscilloscopes, I’ve already figured out that I have better options.

A hint of this is already obvious among the three scopes on Adafruit and Sparkfun. Both the Rigol scopes have 5.7″ 320x24o displays, while the Gratten has a 7″ 800×480 display. Of course, even I know that while a large screen is better, screen size probably shouldn’t be the first, or even fifth thing to judge a scope on. Things like bandwidth, sample rate and memory size, on the other hand, are much more important, and here the Gratten scope matches or beats the Rigol offerings sold by Adafruit. For $400, it offers 100MHz bandwidth and it does so for just $10 more than the 50MHz Rigol scope and $50 less than the 100MHz Rigol. That might be enough to convince them to buy the Atten scope from Sparkfun, me, on the otherhand, I get curious about what else is out there.

What I found is daunting. There are so many options, I’m tempted to buy the Gratten GR1102CAL from Sparkfun and get on with things, but that wouldn’t be like me. I press on.

One of the things I notice in my research is that a lot of these scopes have similar model names. This isn’t exactly a surprise though, because often the numerical part of the name represents some fundamental characteristics. Taking the Sparkfun and Adafruit offerings as an example:

• DS1102
• DS1052
• GR1102CAL

The last/right-most digit on all three scopes is the number two (2). If one were to check out more models of scope from Rigol and Atten (among others), you’d probably recognize that this is the number of input channels. Two channels is common among entry level scopes. Higher end scopes sometimes have 4 channels.

With enough perspective, it becomes obvious that the middle two digits often indicate the bandwidth offered by the scopes: 100MHz or 050MHz in the case of these examples.

The meaning of the first digit seems to indicate the model line, and the letters at the end often indicate key options, like memory size.

The similarities don’t end with just the numbers though. Model names between manufacturers seem very similar. Sometimes even the names seem similar. For example, there is the Gratten GR1102CAL sold by Sparkfun, and there is another manufacturer called Atten, which has a model SDS1102CAL; the specs are pretty much identical between the two. In fact, the case is too, down to the position of the front USB port. Oh, and then there is the Siglent SDS1102CAL, also with remarkably similar specs and appearance.

There is an explanation though, which is that some manufactures sell the same or similar equipment under multiple brands and/or sell equipment which other brands sell under their own label. This simplifies things somewhat, if you can keep everything straight.

I learned something else too, which is that while the Rigol scopes Adafruit sells were revolutionary revolutionary for the value they offered when they first came out, they are a bit long in the tooth now. Last year Rigol released the DS1000Z series, which occupies the same price point the DS1000 series originally did when it came out.

I’ve learned a lot more about the options available for good entry level scopes. Now I’m really sure that I don’t know what to buy. Narrowing down my options will have to be the subject for a new post

My new project is going to involve testing and designing electronics, and so I find myself in need of a bunch of tools I don’t have. Foremost among them, is an oscilloscope, so I can probe circuits in devices to try and understand how they work, and why they don’t work.

My overall electronics aptitude is pretty mediocre. I had a job soldering connectors to serial cables when I was a kid, but my soldering skill isn’t very high and most of the electronic theory I learned in my introductory physics course in college is long forgotten. I have used an oscilloscope though. I used one when I learned about electrophysiology techniques for looking at the activity of individual cells, and I also used one to tune the video system of a cell-florescence microscope to take full advantage of its dynamic range.

More important than what I’ve done with oscilloscopes is that I know what I’d use one for now. I think it will come in handy for looking at the operation of DC-DC power supplies, and just generally for probing circuits. Beyond that though, I’m a novice, and so I went looking a place to get advice. Actually, I didn’t have to look, because I’d already found the EEVBlog Forum, which even has a special section where people are supposed to go easy on beginners for asking dumb questions. Still, they ask that you provide plenty of information when you ask a question, so I had to do some shopping on my own, so I could get a sense of the questions I should ask, and the background I should give.

My first stop was to see what Sparkfun and Adafruit, two online stores that specialize in electronics for hobbyists, were offering. Adafruit has two options, one a 50MHz, two-channel Rigol DS1052E digital storage oscilloscope, the other, a Rigol DS1102, is very similar, but has 100MHz bandwidth. Sparkfun offers the Gratten GA1102CAL, which is also a 100MHz, 2-channel digital scope. They also have two USB scopes for use with your computer, the MSO-19, and MSO-28 from link instruments. Sparkfun and Adafruit also both carry the small, inexpensive DSO Nano and/or DSO Quad.

I’d been considering a DSO Nano or Quad because of their low price and compact size, but people who seem to know better hate them, first because their user interfaces are difficult to use compared to a real oscilloscope, but also because they can’t actually do much. Of course, my needs, as I understand them, aren’t that demanding. I think the signals I’ll be looking at are in the 1-2MHz range, which should be within the capabilities of the DSO Quad, but it doesn’t leave a lot of headroom, and at $200 bucks, its a bit too expensive given that you could get a more capable used analog scope for less, or a new digital scope for another $50-100 more.

I also considered a USB scope. They are more compact, and I also assumed they’d be cheaper, since they didn’t have to include a screen or UI, and I also thought it might make it easier to work with the data on a computer. I was wrong on multiple counts. USB Scopes are a bit of a niche item when compared to a benchtop scope, because regular O’scope users find physical knobs and buttons more productive and easier to use than the often poor software that ships with USB scopes. As a result, volumes are lower, and there is less competition to drive prices down. Moreover, screens are pretty cheap these days, so eliminating one isn’t a huge cost savings. Put the two together, and a decent USB scope is about as expensive as a dedicated scope with similar specs, and you can hook most dedicated scopes up over USB if you need to anyway.

Exploring the existing options helped me think through what I needed and why. I was ready to ask the experts over on EEVBlog. I’ll cover that in my next blog post.