An oscilloscope is one of those tools you don’t think you need, then when you finally cave in and buy one, you wonder how you ever managed without it. Sadly, they’re typically bulky, so they’re not ideal for anyone without a proper workshop. However, the march of technology allowing for the abandonment of cathode-ray tubes (CRTs) in favour of liquid-crystal displays (LCDs) has certainly helped in that regard. They’re also usually expensive, heavily proprietary and awkward to use, which is why I was so interested to find the Digilent OpenScope MZ raising funds via Kickstarter earlier this year.
As the name suggests, the OpenScope MZ – a replacement for the company’s older OpenScope design – is open in terms of both its software and hardware. The company makes all the designs and source files readily available, even down to an optional housing, which is made to be 3D printable on even modest hobbyist printers.
Unlike rival devices, the OpenScope MZ lacks a display, relying instead on a connected device to act as both the user interface and the display. In its most basic mode, the scope acts as a simple USB-serial device, listening for commands and spitting back data. Plus, if you fancy a bit of bare-metal interaction, it can be addressed programmatically and integrated into other scripts. Most users, though, will be relying on Digilent’s open source WaveForms Live software.
Designed to mimic the interface of a more traditional oscilloscope, WaveForms Live runs entirely within a browser window and connects to the OpenScope MZ either via USB through a small translation application that’s compatible with Windows, Linux, and macOS, or over the network via the OpenScope MZ’s built-in Wi-Fi connection. In the latter mode, the OpenScope MZ becomes truly crossplatform: within minutes of unpacking it, I had the device connected to my smartphone, although the compact display was undeniably cramped.
WaveForms Live gives you full access to the OpenScope MZ’s capabilities – an advantage of Digilent’s open approach. None of its abilities is locked away behind licensing keys, as with proprietary devices, and the list includes two oscilloscope channels, a signal generator and digital input-output pins that can double up as a logic analyser. It’s all shown on a large and attractive waveform display, which takes up the bulk of the screen.
Anyone who has used an oscilloscope before will be immediately at home with the OpenScope MZ. You can capture data based on user-configurable triggers, and you can zoom, pan and scroll the resulting data, set up cursors and even perform automatic mathematical functions, such as frequency analysis and root-mean square (RMS) calculations. There’s a fast Fourier transform (FFT) function too, and the data can be exported in comma-separated value (CSV) format, or in PNG image format, at any time.
That’s not to say you should immediately throw away your Agilent or HP oscilloscope if you have one though. The OpenScope MZ is built to a budget, and it shows in the specifications – a PIC32 MZ microprocessor running at 200MHz limits its capabilities to 2MHz of bandwidth and 6.25 megasamples per second (MS/sec). If you need major
bandwidth, the OpenScope MZ isn’t for you, but as a low-cost introduction to oscilloscopes and audio-frequency usage, or as a quick diagnostic aid for hobbyist electronics, or even for educational use, it truly shines.
There are also reasons to reach for the OpenScope MZ over higher-powered devices, even with its limited bandwidth. The Wi-Fi connection, in particular, is a major boon; I could hook up the oscilloscope to a device on my workbench at one side of the office, then begin taking measurements from the comfort of my main desk at the other side. What’s more, by powering the OpenScope MZ via a USB battery pack I had absolute freedom of movement, without the awkward fumbling of a hand-held oscilloscope such as my Velleman HPS140, which, painful user interface aside, does admittedly beat the OpenScope MZ’s specs with its 10MHz of bandwidth and 40MS/sec sampling rate.
A feature sadly missing – and a sign of the OpenScope MZ’s hobbyist nature – is a BNC connector for a real probe. While the bundled 2.54mm female-to-female cable loom – cleverly keyed so you can’t connect it upside down – provides colour-coded access to all the various features of the OpenScope, the ability to connect a proper probe with 1x/10x switching and fine-point spike would have been welcome.
Digilent is selling the OpenScope MZ from its US website at http://store.digilentinc.com for $118 (around £91 ex tax), or at $89 (around £69 ex tax) without the accessory kit, which puts it into direct competition with devices such as the SainSmart DDS-120 (which costs £50 inc VAT from www.amazon.co.uk). While the SainSmart might boast higher specifications and proper probes, Digilent’s software is significantly better, it’s properly cross-platform and the Wi-Fi connection is a real boon. If the company can follow up with a higher-bandwidth model in the future, I’d be hard pushed not to upgrade.
The board is designed to be used bare, or it can be fitted into an open source 3D printed case
The OpenScope MZ may not be the best-performing oscilloscope, but it’s certainly compact
The WaveForms Live software is attractive, easy to use and it works in any modern browser
The low-power PIC32 powers the OpenScope MZ, but limits its performance
The Wi-Fi connection is a killer feature – more oscilloscopes should include it
The basic cable bundle is functional, but there’s no option to use a real oscilloscope probe