Written by: Martin Rowe – October 09, 2015 – EDN Network – http://www.edn.com
Over the last few years, USB oscilloscopes have certainly grown in usefulness and in popularity. Unless you need the highest speed, you can probably find a USB oscilloscope to meet your need at prices from around $100 to several thousand dollars, depending on speed, bandwidth, and features. The SmartScope from start-up company LabNation may come in at the low end of that price range, but is has an array of features that go beyond just a basic oscilloscope. With some improvements, it could make a worthy tool for your home bench or toolbox.
Touted as an oscilloscope by and for makers, the SmartScope’s claim to fame is its ability to operate under a wide range of operating systems: Windows, Linux, Mac OS, Android, and iOS. I tried it on a Windows 7 laptop because I don’t have an Android device (using my wife’s phone is out of the question) and to use iOS, you first have to “jailbreak” the device. Plus, many engineers would rather use a laptop computer for real work, anyway.
Over the next few pages, I’ll show you how the SmartScope looks, feels, and works. I’ll look at it feature by feature.
- Analog channels
- Logic analyzer & bus decoder
- Waveform generator
- FFT and waveform math
- Observations and conclusions
The SmartScope comes in a solidly-built metal case that should act as a good EMI shield for both emissions and immunity. One end of the unit holds the usual BNC connectors for its two analog channels. The opposite end contains a mini-USB connector that communicates with the host device. A micro-USB connector lets you attach a power bank should you need additional battery power in a portable application (the SmartScope is bus powered) and for synchronizing additional units when you need more channels. A 16-pin AUX I/O connector provides access to an external trigger input, the AWG (arbitrary waveform generator) output, eight logic inputs, and four general-purpose digital I/O lines. Two pins provide ground connections.
The box (Figure 1) contains two 60-MHz analog oscilloscope probes, eight clip leads for the digital inputs, and a ten-line ribbon cable that lets you connect to the I/O connector. You also get a mini-USB cable and a micro-USB cable.
Figure 1. The LabNation SmartScope comes with probes for analog and digital inputs.
Software installation and startup
Before connecting the SmartScope to my laptop PC, I downloaded the software and tried to install v4.1.2. LabNation requires that your Windows PC have Microsoft .NET 4.0 or higher, which mine didn’t. The SmartScope software attempted to download and install .NET, but failed. I downloaded the latest .NET version manually. After that, the SmartScope software installed without a glitch.
On initial startup, the SmartScope software displays a help menu (Figure 2) that shows you how to control basic oscilloscope functions such as time and voltage scales, viewfinder, and waveform movement using touch, mouse, and keyboard operations. You can invoke the help by pressing the F1 key. I found myself referring to this screen several times during my tryout. If you need more help, you can view the manual online.
Figure 2. The help screen shows you how to operate the SmartScope’s basic controls.
Take note of how to change voltage and time scales with a mouse. The software designers assumed you’d use an external mouse because to change those settings—you must use the scroll wheel. When I started this evaluation, I was using the laptop’s mouse pad. Without the external mouse, you must use the keyboard to change voltage and time settings. At that point, I connected a mouse.
The heart of any multifunction oscilloscope is, well, the oscilloscope. The SmartScope has two analog channels with the ability to add more channels by adding more units through the micro-USB port. When you start the software, it defaults to a light shaded screen, which you can change to a dark screen. After you clear the help menu by clicking somewhere outside of it, you’ll see a screen something like that in Figure 3. The waveform shown is just stray 60 Hz AC, which the probe and cable picked up.
Figure 3. The basic screen lets you view analog channel specifics by clicking on the ChA or ChB buttons as well as seeing system characteristics.
The screen in Figure 3 shows the oscilloscope grid consuming the entire PC screen. Clicking on the LabNation icon in the lower-left corner brings up a configuration menu, shown in Figure 4. I started testing with a basic signal, a 1 kHz, ±2 Vpk-pk sine wave generated by an old HP oscilloscope demo board.
Figure 4. The analog oscilloscope lets you see the portion of the waveform that’s displayed on the screen.
Note the colored “band” that highlights the minimum and maximum peaks. No other oscilloscope I’ve used shows this band, which seems to indicate which channel you’ve selected. Clicking outside the waveform’s peaks turns the band off. Is it a feature or a bug?
For triggering, the SmartScope has three options that are accessible from the trigger menu on the bottom left side of the screen.
- auto triggering
- require trigger
- single trigger
“Require trigger” is an odd choice of name. We’re used to seeing “Ext. Trigger” as a trigger option.
To select the trigger type, such as edge trigger (rising or falling), click on the trigger circle to the right of the grid. You can then move the circle to raise or lower the trigger level.
I found the waveform trace difficult to see on the light (standard) background; I prefer a dark oscilloscope grid. The System menu in Figure 4 lets you change to a dark display. Figure 5 shows the same waveform using the dark display. Unfortunately, you’re stuck with orange color for ChA and blue for ChB, but at least they are both visible on the light and dark displays, more or less.
Figure 5. I much prefer the dark display. Unfortunately, you can’t change the waveform color.
Next, I generated a signal using a National Instruments VirtualBench system, which served as a “sanity check” for the SmartScope. The 1 kHz sine wave looked essentially identical on both screens.
While a 1 kHz sine wave let me see that the SmartScope worked, it’s not all that useful. Using the VirtualBench function generator, I set up a 5 MHz square wave. Remember that the SmartScope’s rated bandwidth is 30 MHz, which is enough to retain the fifth harmonic of the square wave, with some margin. I used a BNC-to-BNC cable to connect the VirtualBench function generator to the SmartScope’s input channel B. Here’s the waveform displayed first on the VirtualBench screen (Figure 6). You can see what looks like ringing.
Figure 6. A 5 MHz square wave shown on a National Instruments VirtualBench system.
Figure 7 shows the same waveform on the SmartScope screen. Here, you can see how its lack of bandwidth distorts the signal, rounding off the corners. As expected, the SmartScope’s low bandwidth produced the same result at 1 MHz. That’s because it still filtered out the high frequency content in the waveform’s rising and falling edges.
Figure 7. The SmartScope’s 30 MHz analog bandwidth distorts even relatively low-frequency signals.
Figure 8 shows a close-up of the waveform as measured on the VirtualBench, Here, ringing on the square wave’s rising edge is clearly visible, not so on the SmartScope.
Figure 8. Ringing on the waveform was lost with the lower-bandwidth SmartScope.
The LabNation Smartscope provides eight logic inputs for debugging digital designs. Here, I found the software easy to use for both the logic analysis and serial-bus decoding functions, but the provided hardware was awkward to use.
To get eight logic signals, I returned to the old HP demo board. Because the board already had a pin header, I used the SmartScope’s ten-wire ribbon cable (Figure 9) to connect between the AUX connector and the demo board. While the color coding is helpful, I can just see myself separating the wires for the next application, then losing a few.
Figure 9. This ribbon cable provides access to the SmartScope’s AUX connector.
Figure 10 shows a nice feature of the SmartScope software, for it displays the time between transitions. If you click on any channel, you’ll get those measurements. Moving the mouse over another channel displays the measurements for that channel while retaining the clicked-on channel’s measurements. Before taking the image, I had clicked on channel 4, then scrolled the mouse over channel 3 to channel 2, then captured the screen image.
Figure 10. The SmartScope automatically displays the time between transitions when using the digital inputs.
You can set up a pattern trigger based on the digital inputs. Clicking on the right side of each signal unfolds a menu where you can select logic 1, logic 0, rising edge, falling edge, or don’t care condition.
Serial bus decoder
The SmartScope has several serial bus decoders that you can apply to analog or digital channels. I tried the decoder using digital channels. My test bus came from a Rohde & Schwarz demo board, which generates SPI, I2C, CAN, and UART signals. I used the board’s SPI output and connected the board to the SmartScope through three wires. Here’s where making the connections was difficult.
Figure 11 shows four clips connected to the demo board. While it looks easy to do, the jaws that extrude from the clip’s housing are at an odd angle to the housing. They will force you to rotate your hand by 90 degrees from what is most comfortable. The same applies when using the clip to connect to an SMT IC package lead. Connecting to the board was even more awkward because I didn’t want to separate the individual wires from the supplied ribbon cable. The clips fell off several times.
Figure 11. Connecting the clips to a target may look easy here, but it was awkward.
I used one analog channel to verify that the demo board was producing signal, which it was. Then, I connected digital channels D0, D1, and D2 to the board’s SPI port. At first, the SmartScope didn’t show anything until I realized the ribbon cable wasn’t on the right AUX connector pins. Once properly connected and with the decoder set to SPI through the main menu, the SmartScope displayed the following decoded waveform (Figure 12).
Figure 12. The SmartScope decoded data from an SPI bus input.
The SmartScope has a function/arbitrary waveform generator that you can use to create test signals. Accessible from the AUX connector, the waveform generator produces the usual sine, square, triangle, and sawtooth waves plus sawtooth+sine and multisine signals. It also lets you upload arbitrary waveforms from a local file or from Dropbox. From the AWG menu, you can use sliders to set the signal’s frequency, amplitude, and amplitude modulation. In addition to using the sliders, you can activate a virtual keypad to enter your desired values. Invoke the keypad by double-clicking on any of the numbers in the AWG menu. If you use the dark color scheme, the keypad’s numbers will be invisible. The software should know which color scheme you’re using at adjust colors accordingly. Figure 13 shows the keypad, but with the numbers invisible.
Figure 13. A keypad for entering waveform values is partially hidden when using the dark color scheme.
After setting up a sine wave, I was ready to try it, but the SmartScope gave no output. I checked the AUX connector three times and I was using the right pin. There was no indication of how to enable the AWG. At that point, I had to refer to the online manual for help. To start the waveform, you must click on the “Upload function” choice in the menu, shown in Figure 13.
The SmartScope has rather limited math functions, which should be expanded in future software revisions. All you get for math is ChA+ChB. The LabNation engineers should at least add A-B and A×B functions.
I then went back to the analog oscilloscope to try the FFT (Fast Fourier Transform) feature, which is essential for almost any kind of troubleshooting. I used the 5 MHz square wave to try the FFT. The resulting frequency plot was almost as expected.
With the SmartScope, you get a nice selection of windows to apply to a time-domain signal before converting to the frequency domain. Windows include Blackman-Harris, Hamming, Hanning, Flat Top (rectangular), Kaiser-Bessel, and Uniform.
After you set the FFT parameters, a frequency plot appears below the time-domain plot. As expected, I saw peaks at the fundamental 5 MHz frequency and odd harmonics, 15 MHz, 25 MHz, etc. But the peaks were much wider than I expected (Figure 14). Changing the window function didn’t help. When I stopped the oscilloscope, the peaks became narrow spikes, more like I expected. See Figure 15.
Figure 14. While the oscilloscope ran, FFT peaks were wider than expected.
Figure 15. Once the oscilloscope stopped, FFT peaks became narrow.
The $229 SmartScope has potential as a troubleshooting tool, but it has its quirks and needs some improvements.
- The oscilloscope needs something on the screen to let you adjust vertical and horizontal resolution. With the PC version (no touch screen), you must use your mouse’s scroll wheel or keyboard. LabNation needs to add onscreen boxes that you can click or touch to change voltage and time settings. Most oscilloscope users expect that. Some PC-based USB oscilloscopes even have virtual knobs.
- There is no Autoset feature. Oscilloscope users expect that now.
- Users need the ability to change waveform colors.
- Add a DMM (digital multimeter). That software upgrade will add value to the SmartScope.
- The logic probe clips are hard to use. They come apart easily.
- Add a pulse-width trigger.
- Add a button to save a screen image to disk. You shouldn’t need to use print-screen to get an image.
- Add a 16-pin connector to the kit with easy-to attach wires or pins instead of having the ten-wire ribbon cable. That will make connecting to the AUX connector easier and prevent the loss of wires once they come apart from the others on the ribbon cable.
- The digital-signal clips have a sharp pin on their top that extrudes from the housing. It’s for attaching the connectors on the ribbon-cable’s wires. When cleaning my bench after the evaluation. I grabbed the clips in my hand. Those pins can puncture your skin.
In a conversation with me held prior to the SmartScope’s release in September, LabNation’s Reimer Grootjans said “To appreciate the SmartScope, you need to use it with a tablet or smart phone and the pinch interface.” He also claimed that the SmartScope is a tool for makers, who tend to be software developers. “If they can’t use the touch screen,” he said, they will think the device is broken.” Perhaps, but anyone who has ever used an oscilloscope before will have expectations that the SmartScope doesn’t meet at this time. In some ways, I had the distinct feeling that the LabNation user interface was designed for touch screens, with the traditional PC interfaces as afterthoughts.
Established in 2004, NorthTree Associates (Cologne, MN) is a North American distributor that specializes in providing unique Electronic Test & Measurement tools for design engineers, test engineers and production engineers. You can visit our website at http://www.northtreeassociates.com for more information on the LabNation SmartScope