OpenS­cope MZ

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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

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