Last time I introduced you to two relatively inexpensive and somewhat portable scopes: the EM125, which is a cross between a digital voltmeter and an oscilloscope, and the Wave Rambler, which is a scope probe with a USB connector attached. Both of the devices cost about $100, and both have their plusses and minuses.

This time, though, I wanted actually to look at some real-world signals. To make that easy, I grabbed yet another scope-like thing I had handy: an Embedded Artists Labtool. This is an interesting board in its own right. It is an LPC-Link programmer attached to an LPC ARM board that has several high-speed A/D channels. However, I’m not using any of that capability for now. The board also has a cheap ARM processor (an LPC812) on it that serves only to generate test signals. The idea is you can use the Labtool in a classroom with no additional equipment.

The Labtool’s demo CPU generates a lot of different signals, but with only one channel on the test scopes, it didn’t make sense to look at, for example, I2C data. So I stuck with two different test signals: a varying pulse width modulation signals and a serial UART transmitter.

Baseline Signals

To get an idea of what the signals ought to look like, I measured them both with my current favorite bench scope, a Rigol DS1104Z. As you’d expect, it was easy to capture the signals on this scope. Here’s the PWM.

In this case, the PWM was at nearly 99% (you can read that out at the bottom of the screen). The LPC812 cycles this output from 0 to 100% fairly quickly and I happened to catch it at that point. The UART is slightly more challenging since it sends a burst of data with a long gap in between. By using normal triggering (instead of auto) the display nice and stable:

Naturally, a single event trigger would work too. The Rigol, of course, could also decode that UART string, a feature none of the other scopes here could match. Of course it isn’t a $100 scope, either. For reference, the 50 MHz version is about $400. Then again, it has four channels, so its cost per channel isn’t really more than the two scopes we are looking at.

Using the Wave Rambler

The Wave Rambler uses some Windows software and my main desktop doesn’t run Windows at all. However, I do have a very cheap Windows tablet that is serviceable and has a full-sized USB port. When I first ran the software on the tablet, I was confused that the screenshots in the documentation didn’t look right at all. It turns out the tablet’s default setting is to have 125% zoom on the screen. This caused the Owon software to incorrectly compute the location some user interface elements and they were drawn off the screen. The solution was to reset the zoom level in the Windows control panel.

Connecting the scope probe to the circuit wasn’t hard. There’s a spring hook like you’d find on a normal scope probe, although there is no skirt for your fingers to grab when pulling it down. Between that and the size of the probe itself, using that is fairly awkward. You can remove the spring hook if you just want to probe, again, just like a regular scope probe.

The device comes with two grounding methods. There is a clip lead for general use and a little spring that lets you ground to a test point ground. This is useful at high frequencies to avoid inductance in the ground wire. However, at the 25 MHz rating of the instrument, you probably won’t be looking at anything that needs that.

The software looks like it belongs to a larger scope. You can see there are provisions for multiple channels, for example, even though the Wave Rambler only has one channel. There are features you probably won’t use, like pass/fail matching. However, this is a real strength to the Wave Rambler. Need an FFT? The software does that. Want to export the data? Easy to do.

The software’s interface is a little unorthodox, but it works fine. You can select several trigger modes (edge, pulse width, and slope). You can add measurements to the display just like the Rigol does. Here’s the PWM capture, for example.

You can see the measurements at the bottom of the trace. The home icon is where most of the menu selections reside, although pressing some on-screen elements will do obvious things like change from AC to DC coupling. The large A at the top of the screen is the auto settings, which can be handy with a small scope like this.

You can use the software to set what parameters the little track ball controls. Honestly, I didn’t find the trackball very useful so after a few tries I ignored it and just used the software settings. Your mileage, of course, may vary.

Since the software provides a variety of trigger modes, it was easy to capture the UART data, although the software won’t offer to decode it for you:

Overall, the results were pretty good, if you can get used to the awkwardness of using a big fat scope probe. I wish the software ran on other platforms or, at least, there was Sigrok support for the device (which would also take care of the data decoding).

Using the EM125

The EM125 is certainly handy. With the kickstand, a charged battery, and a normal scope probe, there were not a lot of strange wires or awkward connections. It also didn’t need a laptop or a tablet. Depending on what you want to do, that could be a good thing or a bad thing.

It is good for portability. You can throw the EM125 in your tool kit and you don’t need much else. It comes with a nice case and I put a USB charging cable in it along with a small set of tools. The downside is you can’t do all the fancy things the Wave Rambler does in software, so you’ll find no FFTs, no captured images or data, and nothing beyond basic triggering.

Here’s an actual photograph of the EM125 reading the PWM output from the board:

You can see the backlight is nice. The display, though, is a bit confusing. On the top right there are three icons. These icons, along with the two text items below them, are the menu system. You use the arrow keys to go left and right to select an icon. Then the up and down buttons make changes. The first icon sets if the device is a scope or a meter. The second sets the trigger mode. The current mode is essentially an auto mode which is suitable for this capture. The third icon lets you set the trigger level.

If the menu cursor goes down to the numeric fields, you can set the volts per division (currently 2V) and the time base (currently 10 us). The other text and icons are informational (the frequency, the voltage, the current run/stop mode, the input coupling, and the battery charge).

Pressing the left key and holding it will toggle the back light. Pressing the right key and holding it will cause the scope to do an auto set when you release the key. So operation is simple, but then again, the results are simple as well.

I was afraid the UART output would present a small problem since the scope doesn’t offer a choice between auto and normal trigger modes directly. However, it appears that when the trigger mode icon looks like a plain square wave, it is in auto mode. If you select a rising or falling edge, the scope enters normal mode. That means that until a trigger occurs, the instrument will hold the last image. That makes the UART output easy to capture.

Notice the arrow on the falling edge of the square wave in the trigger mode icon? That’s normal triggering on the falling edge. There is no single trigger mode, although if you are quick enough you can press the hold button, though that can be frustrating.

Conclusion

As I mentioned in the first installment, if you are buying one scope, you ought to try to buy something better than this. You can easily get a nice new scope for a few hundred dollars and used scopes can be found that don’t cost any more than either of these two. However, these little scopes do have their place. The Wave Rambler gives you almost as good performance as a traditional scope, as long as you have a PC nearby, only need one channel, and are reasonably dexterous. The EM125, on the other hand, has edged out my normal volt meter in my travel tool kit. Having a scope–even a limited one–is so much better than just having a junk meter, that it is worth the investment.

Of course, if you really want portability, maybe you’d be interested in a watch. If $100 or even $400 is too cheap for your blue blood, maybe you’d like a 62 GHz scope, instead. If you decide on that one, you might want to cash in a Powerball ticket first. That scope runs about a half million dollars!

Do you have a touch-screen oscilloscope? Neither do we. But how cool would that be to pan left and right or expand either axis just like you do on your cellphone screen? [Igor] did just that, and the results (in the video below the break) look fantastic.

We’ve covered [Igor]’s previous round of hacking on his Siglent scope, where he bricked it by flashing the wrong firmware, and then fixed it by Frankensteining the screen into the box that the firmware wanted. But once he’d gotten the scope-hacking bug, he couldn’t quit.

A brief overview: an Arduino Nano reads the touchscreen and sends the commands to the scope to act accordingly. [Igor] initially wanted to simply use the COM port on the back to control, but his previous mis-flashing of the firmware had rendered that moot. Instead, he went after the data bus that interfaces with the keyboard unit, reverse engineered its protocol, and spoofed keypresses with custom code in the AVR.

As a side effect of all this, [Igor] could also write a script that controls the scope from his computer, and he ended up re-housing it all in the nice wooden front panel that you see now. It’s more than a step up from the previous covered-in-electrical-tape look, and the new functionality is very very cool. Kudos.

Something very beautiful appeared in our feed this evening, something that has to be shared. [Duncan Malashock] has created an animation of raindrops creating ripples. Very pretty, you might say, but where’s the hack? The answer is, he’s done it as a piece of vector display work on an oscilloscope.

He’s using [Trammell Hudson’s] V.st Teensy-powered vector graphics board. We’ve featured this board before, but then it was playing vector games rather than today’s piece of artwork. The ‘scope in question is slightly unusual, a Leader LBO-51, a device optimized for vector work rather than the general purpose ‘scopes we might be used to. The artwork is written using Processing, and all the code is available in a GitHub repository.

So sit back and enjoy the artwork unfolding in the video. We look forward to more work featuring this hardware.

Though we’ve not featured any vector graphic pure artwork before, we’ve featured quite a few vector graphics projects over the years here at Hackaday. There is this FPGA-driven vector arcade machine, some vectorscope animations from Germany, and of course a Vectrex console brought back from the dead. Does this playable oscilloscope Tetris Easter egg count, or is it a raster?

We’ve been scratching our heads about the various voice-recognition solutions out there. What would you really want to use one for? Turning off the lights in your bedroom without getting up? Sure, it has some 2001: A Space Odyssey flare flair, but frankly we’ve already got a remote control for that. The best justification for voice control, in our mind, is controlling something while your hands or eyes are already busy.

[Patrick Sébastien Coulombe] clearly has both of his hands on his oscilloscope probes. That’s why he developed Speech2SCPI, a quick mash-up of voice recognition and an oscilloscope control protocol. It combines the Julius open-source speech recognizer project with the Standard Commands for Programmable Instruments (SCPI) syntax to make his scope obey his every command. You’ve got to watch the video below the break to believe how well it works. It even handles his French accent.

Better still, it does it all on his computer without sending stuff off into the cloud, so he can tailor the system to fit his needs. (The Julius system takes advantage of a known grammar and a limited set of words to increase its accuracy.) [Patrick]’s setup does use an Amazon service for optional text-to-speech responses, but that could be easily replaced with Festival or any other open text-to-speech engine if you wanted. Everything is in Python and decently documented on [Patrick]’s GitHub.

We’re familiar with Amazon and Google and Apple’s speech recognition applications, but we are big fans of open development. So hats off to [Patrick] for using Julius. We totally agree with him that putting this all onto a dedicated Raspberry Pi would be neat. But with a limited vocabulary like an oscilloscope control set, we can’t help but wonder if it’s possible to pull off something like this on a smaller microcontroller?

Fancy measurement gear is often expensive to buy, but some bits of kit are entirely DIY’able if you’re willing to put a little work into the project. [Christer Weinigel] needed to get some measurements of a differential clock signal that was ticking away around 500 MHz. El-cheapo probes aren’t going to cut it here. They won’t have the bandwidth and most off-the-rack probes are single-ended, that is they’re referenced to ground. [Christer] needed the difference between two balanced signals, neither of which is grounded. In short, [Christer] needed a high-frequency active differential oscilloscope probe, and they’re not cheap. So he built one himself.

The circuit in the probe is really just an instrumentation amplifier design with a modified input stage and a 50 ohm output impedance. (See this article on in-amps if you need to brush up.) With higher frequencies like this, it’s going to be demanding on the op-amp, so [Christer] spent some time simulating the circuit to make sure it would work with his chosen part. Then he made up a bunch of PCB designs and had them made. Actual results matched fairly well with the simulation.

With some minor tweaking on the input damping resistors, he got a tool that’s dead flat up to 300 MHz, and totally usable up to 850 MHz. If you tried to buy one of these, it’d set you back the cost of a few hundred lattes, but this one can be made for the price of one or two if you get the PCBs done cheaply. Of course, the design files are available for your own use. Kudos [Christer].

Edit: By total coincidence, Bil Herd just posted a video intro to differential signals. Go check it out.

And thanks to [nebk] for the tip!

From what we can understand, [ompuco] has built a 2D audio output on top of the Unity game engine, enabling him to output X and Y values from his stereo soundcard straight to an oscilloscope in XY mode. His code simply scans through all the vertexes in the scene and outputs the right voltages into the left and right audio streams. He’s using this to create some pretty incredible animations. Check out the video “additives” below for an example. (See if you can figure out what’s being “added”.)

As a first demonstration application, [ompuco] wrote an oscilloscope drawing application: electricanvas (demo video). You draw lines and electricanvas converts them into audio, and then it’s off to the scope. And have a look at his pyramid demo.

The work is good enough that he’s inspired another forum user, [Pishtaco] to come up with his own phosphor-vectorscope simulation tool, which also looks pretty sweet. If you don’t have an old phosphor scope around, it’s the next best thing. At least it’s fun to listen to music through; a 45-degree line means that the left and right audio channels are similar. Fuzz guitar in only one channel makes a nice hairy ball. Try it out.

We don’t know anything about Unity, and we’d love to see some of [ompuco]’s wireframe code, because this stuff looks amazing! He wrote us back and said he’d release it after it gets cleaned up. We’ll keep in touch.

When you work at Tektronix and they make a difficult to refuse offer for their ‘scopes, you obviously grab it. Even if the only one you can afford is the not-so-awesome TDS1012. [Jason Milldrum] got his unit before cheaper, and better ‘scopes appeared on the market. It served him well for quite a long time. But keeping it switched on all the time took a toll, and eventually the CCFL backlight failed. Here’s how he replaced the CCFL back light with a strip of LED’s and revived the instrument.

Searching for an original replacement CCFL backlight didn’t turn up anything – it had been obsoleted long back. Even his back-channel contacts in Tektronix couldn’t help him nor could he find anything on eBay. That’s when he came across a video by [Shahriar] who hosts the popular The Signal Path blog. It showed how the CCFL can be replaced by a thin strip of SMD LEDs powered by a DC-DC converter. [Jason] ordered out the parts needed, and having worked at Tektronix, knew exactly how to tear down the ‘scope. Maybe he was a bit rusty, as he ended up breaking some (non-critical) plastic tabs while removing the old CCFL. Nothing which could not be fixed with some silicone sealant.

The original DC-DC converter supplied along with his LED strip needed a 12V input, which was not available on the TDS1012. Instead of trying to hack that converter to work off 6V, he opted to order out another suitable converter instead. [Jason]’s blog details all the steps needed, peppered with lots of pictures, on how to make the swap. The one important caveat to be aware of is the effect of the LED DC-DC converter on the oscilloscope. Noise from the converter is likely to cause some performance issues, but that could be fixed by using a more expensive module with RF and EMI filtering.

This is not an original hack for sure. Here’s a “Laptop backlight converted from CCFL to LED” from a few years back, and this one for “LCD: Replacing CCFL with LEDs” from even further back in time. Hopefully if you have an instrument with a similar issue, these ought to guide you on how to fix things.

One of the most ingenious developments in test and measuring tools over the last few years is the Mooshimeter. That’s a wireless, two-channel multimeter that can measure voltage and current simultaneously. If you’ve ever wanted to look at the voltage drop and power output on a souped up electrified go-kart, the Mooshimeter is the tool for you.

A cheap, wireless multimeter was only the fevered dream of a madman a decade ago. We didn’t have smartphones with Bluetooth back then, so any remote display would cost much more than the multimeter itself. Now this test and measurement over Bluetooth is bleeding over into the rest of the electronics workbench with the Aeroscope,  a wireless Bluetooth oscilloscope.

[Alexander] and [Jonathan], the devs for the Aeroscope got the idea for this device while debugging a mobile robot. The robot would work on the bench, but in the field the problem would reappear. The idea for a wireless troubleshooting tool was born out of necessity.

The specs for the Aeroscope are about equal to the quite capable ‘My First Oscilloscope’ Rigol DS1052E. Analog bandwidth is 100MHz, sample rate is 500 Msamples/second, and the memory depth is 10k points. Resolution per division is 20mV to 10V, and the Aeroscope “Deluxe Package” that includes a few leads, tip, clip, USB cable, and case is about the same price as the Rigol 1052E. The difference, of course, is that the Aeroscope is a single channel, and wireless. That’s fairly impressive for two guys who aren’t a team of Rigol engineers.

As is the case with all Bluetooth test and measurement devices, the proof is in the app. Right now, the Aeroscope only supports iOS 9 devices, but according to the crowdfunding campaign, Android support is coming. Since the device is Open Source, you can always bang something out in Python if you really need to.

While this is a crowdfunding campaign, it’s hosted on Crowd Supply. Crowd Supply isn’t Indiegogo or Kickstarter; there are people at Crowd Supply vetting projects. The campaign still has a month to go, but the first few pledges are putting the Aeroscope right on track to a successful campaign.

It is something of a rite of passage for an electronics enthusiast, the acquisition of a first oscilloscope. In decades past that usually meant a relatively modest instrument, maybe a 20MHz bandwidth and dual trace if you were lucky. Higher spec devices were eye-wateringly expensive monsters, not for the Common People.

We are fortunate that like most other areas of technology the world of test equipment has benefited in the last few years both from developments in digital technology and from the growth in Chinese manufacturing. If your first ‘scope is that second-hand 20MHz CRT you will probably secure it for pennies, and the first ‘scope you buy new will probably have a spec closer to those unattainable super-scopes of yesteryear. Gone is the CRT and timebase generator, in its place a TFT, system-on-chip, and super-fast A to D converter.

[Christer Weinigel] has just such an entry-level modern digital ‘scope, an OWON SDS7102. He comments that it’s got an impressive spec for its price, though the input is noisier than you’d expect on a more expensive device, and the software has one or two annoying bugs. Having owned it for a while, he’s now subjected it to a lengthy teardown and reverse engineer, and he’s posted his findings in a succession of blog posts.

[Christer]’s interest lay mainly in the OWON’s digital section, it seems there is already a substantial community paying attention to its analog front end. He’s deduced how its internals are connected, ported Linux to its Samsung SoC in the scope, succeeded in getting its peripherals working, and set to work programming the Xilinx FPGA that’s responsible for signal processing.

The series of posts is a fascinating read as a run through the process of reverse engineering , but he points out that it’s quite a lot of information. If you are just interested in how a cheap modern oscilloscope works, he says, he suggests reading his post in which he recaps on all its different components.

He also makes a plea for help, he’s no slouch on the ‘scope’s software but admits he’s a bit out of his depth on some aspects of the FPGA. If you’re an FPGA wizard with an interest in ‘scopes, he’d like to hear from you.

This isn’t the first time we’ve featured ‘scope reverse engineering here at Hackaday, though it may be more in-depth than others. In the past we’ve seen a Uni-T screen grab protocol laid bare, and an investigation of a Rigol 1054Z.

There’s going to be a new Nintendo console for Christmas! It’s the NES Classic Edition. It looks like a minified NES, with weird connectors that look like the connector for the Wii Nunchuck. There are no other details.

A site called “Motherboard” reports assembling a computer is too hard and a ‘nerve-wrecking [sic]’ process. Tip of the stovepipe to the Totalbiscuit.

When I was in elementary school, the playground had a twenty foot tall metal slide that faced South. During my time there, at least three of my classmates fell off it, and I distinctly remember the school nurse’s aid running past me on the playground with a wheelchair. There wasn’t soft mulch or the weird rubber granules under this slide – just hard, compacted dirt. This slide was awesome, even if it was torn down when I was in third grade. [Brandon Hart]’s kid’s won’t look back fondly on their youth with experiences like these; he built a water-cooled slide in his backyard. He’s getting an 80°F ΔT with a trip to Ace Hardware, probably $20 in fittings, and a drill. Neat.

This is probably better suited for an ‘Ask Hackaday’ column, but [Arsenijs] has run into a bit of a problem with his Raspberry Pi Project. He’s trying to use a planarized kernel module to obfuscate the SPI bus, but he can’t do that because of a oblivated drumble pin. He could, of course, deenumerate several of the GISP modules, but this would cause a buffer underflow and eventually wreck the entire cloudstack. I told him he should use Corrosion, but he seems dead set on his Hokey implementation. If anyone has any ideas, get the glamphs and put it on the grumbo.

The Owon SDS7102 oscilloscope is a small, cheap, two-channel scope that is impressive for its price but noisier than you would expect. This scope has been thoroughly reverse engineered, and now Linux is running on this scope. This Linux scope has a working VGA display, USB host, USB device, Flash, and working Ethernet. The entire analog front end has been reversed engineered, and somehow this is now the most open oscilloscope you can buy.

The ESP32 is Espressif’s followup to their very popular ESP8266 WiFi module. The ESP32 will be much more powerful and include Bluetooth when it’s released in August. Until then, [Pighixxx] has the complete pinout for the ESP32.

If you were to create a Venn diagram of Hackaday readers and oscilloscope owners the chances are the there would be a very significant intersection of the two sets. Whether the instrument in question is a decades-old CRT workhorse or a shiny modern digital ‘scope, it’s probably something you’ll use pretty often and you’ll be very familiar with its operation.

An oscilloscope is a very complex instrument containing a huge number of features. Modern ‘scopes in particular bring capabilities through software unimaginable only a few years ago. So when you look at your ‘scope, do you really know how to use its every feature? Are you getting the best from it, or are you only scratching the surface of what it can do?

[Alan Wolke, W2AEW] is an application engineer at Tektronix, so as you might expect when it comes to oscilloscopes he knows a thing or two about them. He’s spoken on the subject in the past with his “Scopes for Dopes” lecture, and his latest video is a presentation to the NJ Antique Radio Club which is a very thorough exploration of using an oscilloscope. The video is below the break and at an hour and twenty minutes it’s a long one. We make no apologies for that, for it should be fascinating in its entirety for any oscilloscope owner. Even if you find yourself nodding along to most of what he’s saying there are sure to be pearls of ‘scope wisdom in there you weren’t aware of.

We’ve featured [Alan]’s work quite a few times in the past here at Hackaday. Sticking particularly in the mind are his video on time domain reflectometers, and his showing us how to tune an HF antenna array with nothing more than a signal generator and as you might have guessed, an oscilloscope.

How do you measure the value of an unknown inductor? If you have an LCR bridge or meter, you are probably going to use that. If not, there are many different techniques you can use. All of them rely on the same thing my Algebra teacher Mr. Harder used to say back in the 1970’s: you have to use what you know to get what you don’t know.

[Ronald Dekker] must think the same way. He took a 50-ohm signal generator and a scope. He puts the signal output to about 20kHz and adjusts for 1V peak-to-peak on the scope. Then he puts the unknown inductor across the signal and adjusts the frequency (and only the frequency) for an output of 1/2 volt peak-to-peak.

The idea is that the magnitude of the inductive reactance at the half-way part must be 50 ohms (forming a 50/50 voltage divider with the source impedance). [Ronald] does the math derivation in detail, but it works out that the inductor (in uH) is 4570/f where f is the frequency in kHz. In reality, the setting of the 1V reference is not completely necessary, but it simplifies the way he does the measurement if you read the full post.

Of course, there is probably some stray resistance in the circuit, but not enough to make much difference in most inductors. If you have reason to suspect otherwise, [Karen Orton] contributed the math to get to a slightly more complex expression that lets you factor the DC resistance of the coil in your calculations.

This isn’t the only game in town, of course. We like measuring inductors with a grid dip meter. On the other hand, if it’s input or output impedance that you’re interested in, go talk to Elliot.

If there is one instrument that makes an electronic engineer’s bench, it is the oscilloscope. The ability to track voltages in the time domain and measure their period and amplitude is one akin to a light in the darkness, it turns a mere tinkerer with circuits into one in command of them. Straightforward add-on circuits can transform a basic oscilloscope into a curve tracer, frequency response display, and much more, and modern oscilloscopes offer a dizzying array of useful measurement features unimaginable to engineers only a few years ago. And I need your help to pick a new one.

The Status Quo

My first oscilloscope came my way in the early 1980s when my school had a lab clear-out. It’s a dual-beam Cossor, probably from the 1950s, and it proudly boasts a 2MHz – or should I say “2 Mc/s”! – bandwidth. The maker’s plate calls it a “Portable Oscillograph”, because it does have a handle on top and if you are a weight-lifter you can probably carry it some distance. Dusting it off from the garage recesses for this article brought back memories of all those hacked-together circuits made from old TV parts, of seeing for myself the mysteries of the PAL colour burst, and of my home-made spectrum analyser.

The Cossor clearly wasn’t going to cut it for an electronic engineering student, so sometime about 1990 I made the trip to the Aladdin’s Cave  of Stewarts of Reading, and bought a bargain Gould dual-scan ‘scope from the mid 1970s. It has a 20MHz bandwidth, and has been my trusty companion ever since. It’s typical of everyday ‘scopes of the era, and since ‘scopes like it can be found for little more than beer money these days I’d have no hesitation recommending one to anybody looking for a basic piece of test equipment.

A quarter century later though, I have a ‘scope problem. As a radio amateur I’ve always wrestled with the Gould’s low bandwidth. It’s also not the smallest of instruments, and the sheer number of things new ‘scopes can do these days are something I just can’t ignore. It’s time I bought a new ‘scope, and this is where you come in.

Choices, Choices

Instead I will be looking where I suspect a lot of you will too, at the lower-end Chinese digital ‘scopes from brands like Rigol, Owon, Siglent, Hantek, and others. I’m very familiar with more than one of them from use in contracts, hackspaces, and other people’s benches. They are all compact instruments with fairly similar specifications between brands, in fact many models look similar enough to have been made on the same production lines. They will not perhaps have the spec of the multi-thousand-pound ‘scope when it comes to the edges of the envelope in noise or even sensitivity, but the performance they deliver for the price is more than enough for my purposes.

Even homing in on the bandwidth doesn’t give me as clear a picture as it should. For somewhere between £200 and £300 (About $260 to $400) when all taxes are paid, I can buy any of a spread of Chinese 2-channel 100MHz ‘scopes with similar spec. Some of the models even promise a bonus 200MHz upgrade with a software hack, but this is not price-dependent. I’m left looking at differences in the length of the sample memory, and even wondering whether I am sometimes simply being expected  to pay a bit extra to support an emerging brand hierarchy.

The Hackaday readership are a diverse group, among whom alongside the interested readers reside real, not armchair, experts on almost any subject we cover. Some of you will be in my position of looking at new ‘scopes, and many of you will have been through this process yourselves and have the tales both good and bad to tell about your choices. So if you were standing where I am and looking at a budget digital ‘scope, what would inform your choices?

Header images: Binarysequence (Own work) [CC BY-SA 3.0], via Wikimedia Commons

A few weeks ago I asked the Hackaday community for some help and advice in buying a new budget oscilloscope. Thank you very much to those of you who responded both here online and in person among my friends closer to home. I followed the overwhelming trend in the advice I received, and bought myself a Rigol DS1054z, an instrument with which I am very happy. It’s a nominally a 50 MHz scope, but there’s a software hack that can bring it up to 100 MHz. How fast can it go?

This question became a mini scope-shootout after a conversation with my Hackaday colleague [Elliot] about measuring oscilloscope bandwidth, and then my fellow Oxford Hackspace members producing more than one scope for comparison. You know who you are, thank you. I found myself with ready access to several roughly equivalent models and one very high-end one in specification terms representing different strata of test equipment manufacture, and with the means to examine their performance.

I thus had a chance to look at what the extra money secures in performance terms when you buy an instrument, and gain some idea of whether a more impressive badge is worth the outlay. So what follows is not quite a review of oscilloscopes because I’m not going to dive into feature comparisons, but an evaluation of the bandwidth performance of scopes from several different manufacturers.

Bandwidth vs Everything Else

You might think that what matters in a scope is its timebase; that its quickest setting will tell you how high a frequency it can display. And in a sense you’d be right, but if the scope’s internal electronics are only able to resolve a signal at 50 MHz, it doesn’t matter that the screen can trace out faster signals than that — it will just smear the same 50 MHz signal across more squares of its graticule. If you’re looking for wiggles at a higher frequency than that, they just won’t show up. A scope’s _bandwidth_, the highest frequency wiggles that it can resolve, is what we care about with respect to “speed”.

How does one measure the real bandwidth of an oscilloscope then? The simplest way is to give it a voltage transition so fast as to far exceed its capabilities, and measure the extent to which it has trouble catching up. If you feed it a rise time measured in picoseconds and count the nanoseconds of the rise time that it reports, there is a handy formula to derive the 3 dB bandwidth of its electronics from that figure.

Bandwidth (Hz) = 0.35 / measured rise time (S)

In practice it’s convenient to remember that for a rise time in ns the formula returns a bandwidth in GHz.

The fast rise times used for the tests in this article come from an avalanche relaxation oscillator following a design from [Kerry Wong], producing roughly 500ps rise time pulses. It uses the ubiquitous 2N3904 general-purpose NPN transistor, and since it requires well over 100V for the transistor to enter avalanche mode it incorporates a small switching inverter using parts scavenged from a scrap ATX power supply. The whole device is built dead-bug-style on the back of a surplus PCB from a prototype run, and connects to the scope with the shortest possible BNC lead. In this realm of measurement the slightest stray capacitance can cause a significant lengthening of the measured rise time.

To the Scopes!

The scopes I had for my tests were two older models, and three current ones. The older scopes were a Tektronix TDS210 80 MHz LCD model and a LeCroy LC584AXL 1GHz CRT model, while the current ones were a Hantek MSO5102D representing the lower end of the budget market, a 50 MHz Rigol DS1054z representing the upper end, and a 100 MHz Rigol MSO2102A from a slightly higher stratum. This DS1054z had not as far as we were aware had the famous software hack so was still a stock 50 MHz model, however no software hack changes the front end hardware.

Looking at each scope in the order listed above, we’ll start with the Tektronix. This is very similar in appearance to the three newer scopes, being a lightweight portable LCD model. It’s evidently not the latest spec though, with a mono LCD screen, no USB connectivity and a parallel printer port. Thus its screenshot is a photograph.

The Tek’s measured rise time of 4.2 ns gives a calculated 3 dB bandwidth of 83.3 MHz, only just above the quoted bandwidth of the instrument. Some of this figure may be due to it having to be measured by manual cursor placement, looking again at the screenshot they could be closer to the 10% and 90% points.

Moving to the LeCroy, yet again we have a photograph rather than a screenshot. This scope was very expensive when it was new in the 1990s, and it has a 1 GHz bandwidth, but it only sports a 1.44 Mb floppy drive and a thermal printer. Unfortunately we didn’t have a floppy disk, so out came the camera. With a rise time of 679 ps this instrument gave the fastest reading of all we tested, unsurprising given its quoted performance. If we were to feed this figure into the formula above we’d arrive at a 3 dB bandwidth of 515 MHz, so given that this is a 1 GHz scope we are measuring the rise time of the pulse itself. This was using the instrument’s internal 1 Mohm termination because of the voltages involved, its owner suggested that the full bandwidth might require use of its 50 ohm setting and we could thus still be seeing a bit of stretch. At these timings the most unexpected factors can make a significant difference.

The modern trio of scopes are all much more up-to-date in their interfaces, with USB sockets below their colour LCD screens. The Hantek first, it gave a rise time of 2.8 ns, which corresponds to a 125 MHz bandwidth. This follows the trend set by the older model, a modest margin above its quoted bandwidth. This model is reputed to have a software hack that delivers a 200 MHz bandwidth, it’s fairly obvious given this measurement that such a figure would be illusory. In the screenshot you can see a little ringing after the pulse, this is due to the roughly 100 mm BNC lead we were using to couple pulse generator and scope.

The Rigols completed our tests. The DS1054z first, with a 1.4 ns rise time. This gives the instrument a 3 dB bandwidth of 250 MHz, a significant surprise at five times the quoted bandwidth and over twice the bandwidth with the software hack. This scope also exhibited a bit of ringing, though less than the Hantek.

Finally in our selection of instruments came the Rigol MSO2102A. This had a rise time of 1.25 ns, which gave it a calculated 3 dB bandwidth of 280 MHz. Not far short of three times its 100 MHz quoted bandwidth, so yet again it has the same large bandwidth margin as its lower-range sibling.

It may be slightly unfair to compare two slightly long-in-the-tooth digital scopes to three very modern models, but it’s a worthwhile comparison when you consider the manufacturers. Brands like LeCroy and Tektronix are supposed to represent the high-quality end of the market, so we should expect their products to foreshadow the performance of their budget competitors by a decade or so. In particular the Tektronix is a directly equivalent model to the more recent trio in terms of form factor and quoted bandwidth. So in looking at these older models we are not so much looking at their performance compared to the newer ones in a negative sense, more looking to see how far the technology has evolved since their manufacture.

Putting all four models within the range of our pulse generator in a table to compare their figures, we see the following:

At this point it’s fairly obvious that the two Rigols give the most Bandwith Bang For Your Buck among the models tested, extending far beyond their quoted or even hackable bandwidth. Without opening up both instruments it’s impossible to tell, but would we find substantially the same front end chipset in all 200 MHz and below Rigol scopes? Meanwhile when you buy the Hantek you pay a very reasonable price depending where you look, and get exactly what you pay for.

The interesting story comes from the older model. The Tektronix has quite a narrow margin of bandwidth overspecification. This might seem odd for what would have been quite an expensive instrument in its day, but it’s worth considering that digital oscilloscopes were significantly more cutting-edge technology in those days than they are now. When you pay for a digital scope you are in a significant sense buying the quality of its analogue-to-digital converter, and given that ADCs of this speed were quite exotic pieces of silicon in the 1990s it’s hardly surprising that the designers at Tektronix had less margin available to them within the target budget for their product.

The process of choosing a scope and then investigating the performance of digital scopes over the past few weeks has been an extremely interesting one. When you have used these instruments for over 30 years you believe you know everything there is to know about them, but the work documented here has proved there is always something new to learn, and measure.

If you could only own one piece of test equipment, it should probably be an oscilloscope. Then again, modern scopes often have multiple functions, so maybe that’s not a fair assertion. A case in point is the Scopefun open hardware project. The device is a capable 2-channel scope, a logic analyzer and also a waveform and pattern generator. The control GUI can work with Windows, Linux, or the Mac (see the video, below).

The hardware uses a Xilinx Spartan-6 FPGA. A GUI uses a Cypress’s EZ-USB FX2LP chip to send configuration data to the FPGA.  Both oscilloscope channels are protected for overvoltage up to +/- 50 V. The FPGA samples at 100 Mhz through a 10-bit dual analog-to-digital converter ( ADC ). The FPGA handles triggering and buffers the input before sending the data to the host computer via the USB chip. Each channel has a 10,000 sample buffer.

There are also two generator outputs with short circuit and overvoltage protection ( +/- 50 V ). Generator channels have 50 Ohm internal impedance and also operates via the GUI using the same USB chip. The FPGA generates signals at 50 Mhz using counters, algorithms, or simple waveform data and feeds a DAC.

A 16-bit digital interface can be set as inputs or outputs. The FPGA samples inputs at 100 MHz. The output voltage can be set, but inputs are 5 V tolerant.

According to the developer, you can build the scope from the information provided by using free sample chips from the various vendors, only paying for the small components and the cost of the PCB.

We’ve looked at several low-cost scope options before. Labtool even boasts some similar features.

If you are interested in electronics or engineering, you’ll have noticed a host of useful-sounding apps to help you in your design and build work. There are calculators, design aids, and somewhat intriguingly, apps that claim to offer an entire instrument on your phone. A few of them are produced to support external third-party USB instrument peripherals, but most of them claim to offer the functionality using just the hardware within the phone. Why buy an expensive oscilloscope, spectrum analyzer, or signal generator, when you can simply download one for free?

Those who celebrate Christmas somewhere with a British tradition are familiar with Christmas crackers and the oft-disappointing novelties they contain. Non-Brits are no doubt lost at this point… the crackers in question are a cardboard tube wrapped in shiny paper drawn tight over each end of it. The idea is that two people pull on the ends of the paper, and when it comes apart out drops a toy or novelty. It’s something like the prize in a Cracker Jack Box.

Engineering-oriented apps follow this cycle of hope and disappointment. But there are occasional exceptions. Let’s tour some of the good and the bad together, shall we?

The Weaknesses

Of course, it’s not that simple. Modern phones have plenty of processing power, but when it comes to analogue input and output they are restricted to only the hardware they need to make a telephone call. A single microphone input, and a stereo output that can drive a line input on an amplifier, or a set of headphones. Unless you have spent a lot of money on a very high-end phone targeted at audiophiles these will not be served by particularly high-end silicon, the ADC and DAC will top out at somewhere just above the CD sample rate of 44.1kHz and will not have the quietest noise performance. They will not be in any way calibrated, so the best you can hope for from your hardware in terms of measuring ability will be a bandwidth of somewhere just above 20KHz with no ability to produce or measure quantifiable voltages. To give some context, even a 5-dollar USB sound card for your PC will be capable of a higher bandwidth than that you’ll find in your phone.

Our question posed earlier in this piece then becomes “Why buy an expensive oscilloscope, spectrum analyzer, or signal generator, when you can simply download one for free that only has a 20KHz bandwidth and can’t accurately measure or produce a known voltage?” It doesn’t sound very encouraging, does it.

But looking at it another way, you can’t argue with free. If you are working at audio frequencies then perhaps they can offer something useful. Even with their limitations perhaps there are still areas in which they can deliver useful insights, and that’s what we’ll now investigate.

The Strengths

We’ve looked at the shortcomings of a mobile phone as an instrument platform, but does it have any strengths? In one respect here we are fortunate. A phone may not be able to measure voltages accurately, but it should be able to do so when it comes to frequencies and timing. All the actions of its microprocessor will be governed by a crystal oscillator, which while it won’t be calibrated to an incredible standard will still be good enough for the purposes of a free mobile phone instrument.

Even if we can’t entirely trust our phones on matters of amplitude we can do so in this field, if it returns a frequency or period reading we can believe it. Another area in which we can place some trust in our phones lies with waveform generation. Within the limitations of its DAC we know that it is designed to reproduce whatever waveforms a piece of music can supply it, so for the purposes of a very simple audio benchtop instrument we can trust it to produce the sine, square, and triangle waves we’d expect from a basic signal generator.

Having considered the likely usefulness of a mobile phone app instrument and thus having an idea of what to expect, it’s time to sit down at the bench with a phone and try a few for real. This isn’t a review of the apps themselves but a look at the feasibility of an app as an instrument, so we’ll mention a few apps but not review their individual features in detail. Our device for these tests is a Moto G4 running Android 6.0.1.

Signal Generators

We started by looking at the performance of a phone as a signal generator. There are a lot of results for a search on “signal generator” or “function generator”, one of the ones near the top was keuwlsoft’s offering, capable of producing sine, triangle, and square waves from 22kHz down to an improbable-sounding 471.16mHz, as well as a selection of noise sources and modulation effects.

Installed on the phone, it rewarded us with a tone in the speaker after the usual moment to decipher its UI. Plugging in a 3.5mm jack with a lead to our ‘scope, and we could see the three types of waveform as expected. The frequency was measured as exactly the figure in the app. At the upper end of the frequency range above 20KHz it became obvious that the waveform was diminishing and distorting, however that is probably a feature of the Moto’s audio hardware. Otherwise the amplitude stayed pretty constant over the audio range.

On the subject of amplitude, these apps are usually calibrated in percentage of the maximum amplitude they can serve, there is no voltage reading. However to give an idea of the output level, with both the in-app gain and the device volume set to maximum we measured 945mV RMS for a 1KHz sinewave. Knowing that figure it was a simple matter of setting the in-app gain to a calculated percentage to give a lower figure, for example to achieve a 500mV RMS reading we set it to 52.91%. It’s not perfect by any means, but if you have measured the output at full volume it is possible to impose some level of calibration.

Having exercised the phone’s capabilities producing waveforms, it’s time to consider its abilities measuring them. There are a variety of apps freely downloadable that offer either oscilloscope, spectrum analyzer, or a combination of both functionalities.

Input Problems

The first thing we encountered when installing these apps was the nature of Android’s approach to audio hardware. By default these apps take their input from the microphone. Everyone who installs them probably spends a while whistling at their phone to see a nice waveform or spectrum peak appear, but sadly for our purposes a microphone is no use. We need a physical input, and you might think that could be served by the microphone input on the device’s 3.5mm jack plug. Unfortunately a modern phone is not the same as a cassette recorder of old, so we quickly discovered that simply plugging in the appropriate TRRS lead did not magically switch over from the microphone.

Instead that changeover is handled by software, and whether it works for you will depend on how lucky you are in your combination of phone, OS version, and app. We did not find any apps that recognized an audio source plugged into the jack socket by default on the Moto, though a couple of spectrum analyzer apps offered a source selection option in their settings between the built-in microphone, and the line input.

Happily there is an alternative that shouldn’t cost too much if your phone is a fairly recent one. Since version 5 there has been support in Android for USB sound cards, so if you have an OTG cable you can plug one in and reboot the phone to find its default audio input and output now come through the sound card. To test the oscilloscope apps we did this with the Moto and a cheap no-brand USB audio dongle, and it performed very reliably. It’s important to reboot the phone with it plugged in, we found it wasn’t always recognized when plugged in after reboot. It’s also worth noting that even though our USB card is capable of more than CD-quality sample rates there was no provision to enable these in any of the software.

Whichever way you get your working input to your phone, there is one further thing to beware of. A mobile phone input is designed only for use with a headset microphone for making calls, thus it expects a microphone level signal. It will top out somewhere well under 100mV, and anything above that (such as line level audio) will push it into distortion. Further, it does not have anything like the resilience of a real ‘scope input so unless you are only measuring up to about 50mV you will have to build some form of protection circuitry. Have a look at this preamplifier project for an example. For the purposes of our tests when using the Moto’s input jack we wound down our signal generator to an appropriate level for the input.

Spectrum Analyzers

Having now dealt with the prerequisites of getting a signal into our phone, it’s time to look at some apps to use it. Starting with a spectrum analyzer, we found that Vuche labs’ Advanced Spectrum Analyzer offered the ability to select the Moto’s 3.5mm jack as an input, and presented an interface that was easy to get working. When presented with a sine wave it obligingly produced a single peak, and on changing to a square wave it showed the harmonic content as you might expect. It consistently identified the fundamental frequency on the low side by a few Hz, for example showing a verified 1KHz as 990Hz.

On the Y axis it returns a figure in dB. As always the question is “dB relative to what?”, and the answer here appears to be relative to the maximum level quantifiable by the device. So if you have time to calibrate it against a known instrument as described above and do some calculations you could get some idea of  a real figure, however in the majority of cases this scale can at best be considered as indicative only for relative quantization of peaks.

Oscilloscopes

When looking at oscilloscope apps we tried almost every one that the Google Play Store could find for us, and none of them offered an ability to select the Moto’s 3.5mm jack that would work. It’s not to say that none of them support it on other phone and OS combinations, merely that none of them worked for us. So when testing these apps we had to resort to the USB sound card mentioned above, a mild inconvenience but one that a subset of the apps had no problems recognizing.

SmartScope Oscilloscope from LabNation is a companion app to their oscilloscope peripheral which gives the features you’d expect from a “proper” ‘scope, but it also has a mode that supports the phone’s audio input. We liked it because unlike many other ‘scope apps it has a user interface allowing easy pinch-and-zoom selection of timebase period and voltage. In the time domain it’s extremely easy to measure period with this app, but the amplitude domain like those on the other apps can not be trusted when not using their peripheral and would need calibration against a known instrument. It does however handle different waveforms as you’d expect from a conventional oscilloscope, and provides a handy way to look at the shape of an audio waveform.

Cracker Or Bench? Our Conclusions

So after several hours at the bench installing and trying test equipment apps, what do we think? The overwhelming impression is that none of these apps could replace the real instrument on their own using just the phone’s hardware. It’s quite possible that with a dedicated peripheral they could provide a good instrument, but that is beyond this article.

That said, do these apps offer any useful functionality, and is it worth keeping them on your phone? We’d say yes in that a not very good instrument is better than no instrument, but we’d like to qualify that by looking at each case individually.

Signal generators, at least in the audio range, are something at which the apps do a passable job. If your voltage requirements extend only to audio line level and below, and you have no wish to venture above 20kHz, they make a useful audio source that is capable of delivering a variety of combinations of waveform. Definitely useful.

Spectrum analyzers though are not a field in which the phone performs as well as signal generation. These apps are fine in the frequency domain so as long as you stay within the voltage range of the input you can use them to gain a view of what frequencies are present, however the lack of intensity calibration is an Achilies’ heel. It’s probably best to consider these as half-useful, half-novelty.

Oscilloscope apps are sadly closer to the Christmas cracker. Yes, you can see the shape and period of the waveform, but there is only a certain amount of information to be gleaned from these readings. The most useful feature of an oscilloscope as we see it is as an accurate time-domain voltmeter, and without that ability the app becomes significantly less useful. Three-quarters-novelty, quarter-useful.

Could these apps be improved? Definitely if their developers took the time to incorporate input selection to ensure that all users could force them to listen to the microphone jack. Unfortunately the feature that would be most useful, calibration in the voltage domain, is probably beyond the capabilities of a phone’s hardware without buying extra peripherals, which rather defeats the object.

After all, the one thing these apps have going for them is that they cost nothing, and that’s more than you can say for a Christmas cracker. Do you have suggestions for useful instrument apps? Let us know in the comments below.

Browsing YouTube may prove to be your largest destroyer of productive time outside of Hackaday, once you have started looking at assorted Lincolnshire plumbers or young Ukrainians doing dangerous stunts it’s easy to lose an hour with very little to show for it. There is so much to divert our attention, it’s a wonder that any of us ever make anything!

So to ensure you lose a further quarter hour today, we’d like to bring you [Jesper Broe]’s demonstration and teardown of his latest oscilloscope. This might seem unpromising when we tell you it’s a single-trace model with a bandwidth of 10MHz, but don’t give up. This is a RIMEDA C1-112, a portable instrument made in Lithuania when the country was part of the Soviet Union, and its party piece is that it contains a digital multimeter with a vector display using the oscilloscope CRT.

We’re shown the compact device being unpacked, then put through its paces as an oscilloscope. It gives useful results above 10MHz, but it is visibly losing amplitude and eventually it has trouble triggering as the frequency increases. Interestingly all the controls work in the opposite direction to the ones you will be used to, anticlockwise rotation increases rather than decreases. Then we’re shown the multimeter function, which is compared to a modern DMM and found to be still pretty accurate after nearly three decades.

The ‘scope’s lid is then removed, and we see something of the logic boards that produce the digital display. A host of Soviet K155 series logic ICs are at the heart of it, and at the end of the video we’re shown a period review in Russian with a glimpse at the waveforms they produce to vector draw the figures.

Take a look at the video below the break, we’re sure you’ll agree it’s an instrument that many of us would still find useful today.

This is the first Soviet ‘scope teardown we’ve brought you here at Hackaday, but there have been quite a few other instruments receiving the treatment. A Rigol needed a faulty encoder replacing back in 2011, while we showed you the inside of a National Instruments VirtualBench in 2015. The ultimate ‘scope teardown though is the Teledyne LeCroy Labmaster 10-100zi, a 100GHz powerhouse with a million-dollar price tag.

Everyone likes a good light show, but probably the children of the 60s and 70s appreciate them a bit more. That’s the era when some stereos came with built-in audio oscilloscopes, the search for which led [Tech Moan] to restore an audio monitor oscilloscope and use it to display oscilloscope music.

If the topic of oscilloscope music seems familiar, it may be because we covered [Jerobeam Fenderson]’s scope-driving compositions a while back. The technique will work on any oscilloscope that can handle X- and Y-axis inputs, but analog scopes make for the best display. The Tektronix 760A that [Tech Moan] scrounged off eBay is even better in that it was purpose-built to live in an audio engineer’s console for visualizing stereo audio signals. The vintage of the discontinued instrument isn’t clear, but from the DIPs and discrete components inside, we’ll hazard a guess of early to mid-1980s.  The eBay score was a bargain, but only because it was in less that perfect condition, and [Tech Moan] wisely purchased another burned out Tek scope with the same chassis to use for spares.

The restored 760A does a great job playing [Jerobeam]’s simultaneously haunting and annoying compositions; it’s hard to watch animated images playing across the scope’s screen and not marvel at the work put into composing the right signals to make it all happen. Hats off to [Tech Moan] for bringing the instrument back to life, and to [Jerobeam] for music fit for a scope.

I recently opened the mailbox to find a little device about the size of White Castle burger. It was an “Analog Discovery 2” from Digilent. It is hard to categorize exactly what it is. On the face of it, it is a USB scope and logic analyzer. But it is also a waveform generator, a DC power supply, a pattern generator, and a network analyzer.

I’ve looked at devices like this before. Some are better than others, but usually all the pieces don’t work well at the same time. That is, you can use the scope or you can use the signal generator. The ones based on microcontrollers often get worse as you add channels even. The Analog Discovery 2 is built around an FPGA which, if done right, should get around many of the problems associated with other small instrumentation devices.

I’d read good things about the Discovery 2, so I was anxious to put it through its paces. I will say it is an impressive piece of gear. There are a few things that I was less happy with, though, and I’ll try to give you a fair read on what I found both good and bad.

Up Front: The Price Tag

Let’s get one thing out of the way up front. This thing isn’t cheap ($279, list price). You have to look at it from the standpoint of value. You are getting a lot of instruments in one and — unlike some others — you can use them (mostly) at the same time. The other thing I was surprised about is that it came with the usual plug with lots of little wires ending in female header sockets. The reason this surprised me is the scope is pretty capable (see below) which means you really want a good set of probes on it. They do sell a $20 board that has BNC connectors on it (but be sure to get it at the same time as the cheapest shipping is almost $20).

I understand the unit is already pricey for this market, so adding another $20 to it (and more if you included cheap probes) might not be very attractive. But for what the scope is capable of, it really ought to include the BNCs. Looking at the Digilent web site, it appears that they are targeting the education market with this device. That means they’ve priced it high and probably offer educational users discounts, especially in quantity.

The Specs

The scope can do 100 megasamples per second and uses a 14-bit A/D. If you have the BNC connectors, you can get 30MHz. The inputs are actually differential (although the device isn’t ground isolated). The waveform generator can go to 12MHz.

Speaking of the capabilities, here’s what Digilent says about it (with a few edits):

• Two-channel USB digital oscilloscope (1MΩ, ±25V, differential, 14-bit, 100MS/s, 30MHz+ bandwidth – with the Analog Discovery BNC Adapter Board)
• Two-channel arbitrary function generator (±5V, 14-bit, 100MS/s, 12MHz+ bandwidth – with the Analog Discovery BNC Adapter Board)
• Stereo audio amplifier to drive external headphones or speakers from waveform generator
• 16-channel digital logic analyzer (3.3V CMOS and 1.8V or 5V tolerant, 100MS/s)
• 16-channel pattern generator (3.3V CMOS, 100MS/s)
• 16-channel virtual digital I/O including buttons, switches, and LEDs
• Two input/output digital trigger signals for linking multiple instruments (3.3V CMOS)
• Single channel voltmeter (AC, DC, ±25V)
• Network analyzer – Bode, Nyquist, Nichols transfer diagrams of a circuit. Range: 1Hz to 10MHz
• Spectrum Analyzer – power spectrum and spectral measurements (noise floor, SFDR, SNR, THD, etc.)
• Digital Bus Analyzers (SPI, I²C, UART, Parallel)
• Two programmable power supplies (0…+5V , 0…-5V). The maximum available output current and power depend on the Analog Discovery 2 powering choice:
  • 250mW max for each supply or 500mW total when powered through USB
  • 700mA max or 2.1W max for each supply when using an external wall power supply

So even they think the BNC board is important. They also left off one of the coolest features — there is a scripting language all over the place for things like custom triggers or orchestration.

I mentioned you could use most of these things at the same time. There are limits, but they are easy to understand. For example, the network analyzer uses the scope channels and the waveform generator. So if you are using the analyzer, you will tie up those resources. That makes sense.

The device is built on an FPGA so it doesn’t suffer from the problem micro-based ones do with respect to sharing timing. All the instruments work fine at the same time. They do, however, share buffer memory. When you connect, you can select from several configurations. Want a 16K buffer for the scope channels? Ok, but it will cost you memory on some of the other peripherals. It makes sense that there is a fixed amount of memory and it is nice that you can make your own choice for how to allocate, within certain parameters.

Basics

Since the device is just a box with some wires coming out of it, the software is everything. Luckily, the software is cross-platform (thank you for that). It is very busy, because there are a lot of features, so you have to explore things. Most items have balloon help (although some don’t, like the UART trigger dialog). The online help is rudimentary and not likely to help you unless you are really new to this stuff.

Still, you can figure most of it out with a little work. For example, here’s the waveform generation screen with a sine wave that has some noise at the extremes:

The main screens have lots of little buttons like the ones on the scope screen:

See the buttons at the top right? The leftmost one shows an overview of the entire buffer. The second one turns on the hot track cursor (the red automatic cursor visible on the waveform). The gear sets some options and the Y button sets the labels.

The gear button is especially annoying. Look down the right-hand side of that screen. There are three more gear buttons! Granted, those are easy because, obviously, those are options for channel 1 and 2, but in some cases, it is hard to remember exactly which gear button is hiding some obscure option you are looking for.

Digital

The digital section works about the same. You can trigger across instruments (so you can trigger the scope when an SPI value comes in the digital ports). There’s fair protocol conversion for things like UARTs and the like. The documentation on these is pretty sparse, though (or I didn’t find it) so expect to experiment. For example, my normal scopes let me invert an RS232 signal before decoding it. I didn’t find an option for that. Maybe it is smart enough to figure it out. Or maybe I could just flip the scope leads. But without trying it, you can’t tell.

In fact, I had a lot of trouble with the protocol decoding. I wrote a really simple Arduino program just to generate a test pattern:

void setup() {
 // put your setup code here, to run once:
 Serial.begin(9600);
}

int ct=0;

void loop() {
  if (ct++==1000)
  {
    ct=0;
    Serial.write("B");
  }
  else if (ct==1)
  {
    Serial.write("C");
  }
  else
  { 
    Serial.write("A");
  }
  delay(1);
}

My idea was to trigger on the letter B and maybe even watch it with the scope. At first, I didn’t have the delay at the end of the loop. I was sending as fast as I could. I could decode the data, but triggering didn’t work. I didn’t realize it at first, because it was in auto mode, so it would eventually trigger itself and I was perplexed that I couldn’t find the “B” in the data stream.

Once I went to normal triggering, it simply didn’t trigger at all. I theorized that it wasn’t able to figure out which bit was a start bit in the middle of a stream like that. In all fairness, my Rigol DS1154Z couldn’t figure it out either. However, a very brief delay (1 or less) allowed the Rigol to grab the data reliably and trigger. I never got it to work with the Discovery.

In all fairness, a new version of the Analog Discovery software appeared right after that and now it works, although it requires a longer delay between characters than the Rigol does. In addition, the manual trigger button at the bottom of the screen doesn’t appear to work — at least, not while waiting for a serial trigger. Turns out, I later figured out that unlike a manual trigger button on a conventional scope, this button only works if you have the trigger set to manual. You can’t override a normal trigger with the button. Seems like the button ought to be disabled if that is the case.

The UART trigger, it turns out, is just a wizard (see right) that sets a complex trigger for you. You can also trigger on a break or an idle condition. Obviously, you can’t (with this dialog) do multiple characters or anything else exotic. You might be able to do it with the actual complex trigger that it defines for you.

Here’s the actual letter B trigger. There is not much help for some of these screens, including this one. Most of it is easy to figure out, but still, it would be nice to have the balloon help, at least.

The Verdict

It may sound like I’m being harsh on the Discovery 2. I guess I am, but I am actually mostly impressed. The hardware seems to be great. The software needs some work, though. If this were a $50 product, it would be a no-brainer. If the software were open, it would get fixed and enhanced very quickly.

However, it isn’t. For the price of the unit — especially adding in the BNC connectors — you could buy a pretty nice 2-channel scope. True, the Discovery is a lot more than that, but it also has its limitations. We’ve seen cheap function generators, power supplies are a dime a dozen, and there are plenty of logic analyzer options. The network analyzer — if you need it — might be the one game changer. The ability to script everything together could be a big deal, too, if you do a lot of automated testing. It isn’t quite like having GPIB keeping a rack full of gear working together, but in some ways, it is similar and maybe even better for most of us.

On the plus side, it is compact and portable. It is everything in one package at one price. If you really bought all the things the Discovery can do, you’d spend more. But you’d also probably get a little more, too. For example, the largest buffer you can field for the scope is 16K per channel. That’s not much these days.

I was intrigued with the network analyzer and I’ll post when I’ve had some time to play with it. That is the one piece of gear you’d be hard pressed to replace at the price.

Is it good? Yes. Is it perfect? No. Should you buy one? That’s going to be a personal decision. It is too pricey for an impulse buy. It is definitely useful but only you know if it is useful enough to part with a few hundred dollars. Maybe a hackerspace or other group could put together a group buy and negotiate a better bulk price–I don’t know, but it never hurts to ask.

I’ve looked at cheap scopes before, and some of them were PC-based too. They aren’t in the same class as the Discovery 2, but they are also a fraction of the price. The closest thing I can think of to the Discovery 2 is LabTool (which I mentioned obliquely in an earlier post). It is cheaper but suffers from using a microprocessor, so it can’t do everything at once, and the more you do, the fewer samples you can take. On the other hand, it comes with BNC connectors.

Further Review

This review shared my thoughts on the Analog Discovery 2 but I didn’t actually demo it. For more on that you can see a video from Digilent that shows you a lot of the features below. There’s also a video from [Nezbrun] that compares it to the older Discovery that this unit replaces.

Editor’s Note: The review unit for this article was given to Hackaday by Digilent without charge.

What happens when you throw a ball into a box? In the real world, the answer is simple – the ball bounces between the walls and the floor until it eventually loses energy and comes to rest. What happens when you throw a virtual ball into a virtual box? Sounds like something you might need a program running on a digital computer to answer. But an analog computer built with a handful of op amps can model a ball in a box pretty handily too.

OK, it takes quite a large handful of op amps and considerable cleverness to model everything in this simple system, as [Glen Kleinschmidt] discovered when he undertook to recreate a four-decade-old demonstration project from AEG-Telefunken. Plotting the position of an object bouncing around inside the virtual box is the job of two separate circuits, one to determine the Y-coordinate and bouncing off the floor, and one to calculate the X-coordinate relative to the walls. Those circuits are superimposed by a high-frequency sine-cosine pair generator that creates the ball, and everything is mixed together into separate outputs for an X-Y oscilloscope to display. The resulting simulation is pretty convincing, with the added bonus of the slowly decaying clicks of the relay used to change the X direction each time a wall is hit.

There’s not much practical use, but it’s instructional for sure, and an impressive display of what’s possible with op amps. For more on using op amps as analog computers, check out [Bil Herd]’s “Computing with Analog” article.

Thanks to [Frank] for the tip, and for helping [Glen] patch the dodgy Google translation.