IEEE Spectrum March, 2012 - 18

hands on
POCKET SCOPE
ROUNDUP

3

We put three miniature
oscilloscopes to the test

2

E

ver knelt behind-a-home-theater-
receiver,-tangled-in-wires,-trying-
to-figure-out-why-nothing's-
coming-out-of-the-stereo-speakers?-
Is-the-cable-bad?-Is-the-cable-box-even-
putting-out-the-digital-audio-signal?-
Oh,-if-only-you-could-whip-out-a-scope-
from-your-pocket-and-check.-As-it-
turns-out,-you-can.-Here's-a-look-at-
three-pint-size-oscilloscopes.
Perhaps-the-most-ambitious-pocket-
scope-yet-attempted,-the-DSO Quad (1),-
from-Seeed-Studio,-is-smaller-than-a-
smartphone.-It-offers-four-input-channels-
(two-analog,-two-digital),-a-gorgeous,-
high-contrast,-active-matrix-color-screen,-
and-measurements-galore.-Peak-topeak-voltage,-duty-cycle,-frequency-you-
name-it-and-this-scope-will-measure-it.-
That-is,-once-you-calibrate-the-thing!-The-
Quad-comes-completely-uncalibrated,-
requiring-you-to-adjust-tiny-trimmer-
capacitors-and-perform-a-multistep-
firmware-voltage-calibration-as-well.
All-this-power-is-wrapped-up-in-one-
of-the-most-convoluted-user-interfaces-
I've-ever-seen.-Eventually,-you'll-get-the-
18

NA * iEEE SpEctrum * mArch 2012

hang-of-its-four-push-buttons-and-two-
multipurpose-swivel-controls,-which-
move-back-and-forth-and-also-up-and-
down.-The-interface-will-surely-improve,-
because-the-Quad-is-an-open-source-
project.-Such-goodies-as-audio-frequency-
response-plotting-and-fast-Fourier-
transform-analysis,-as-well-as-bug-fixes,-
have-been-released-or-are-in-development.
Remarkable-as-it-is,-the-Quad-is-still-
more-of-a-hobbyist's-gadget-than-a-serious-
instrument.-Despite-its-admirably-fast-
sampling-rate,-the-op-amp-based-analog-
front-end-exhibits-quirky,-inconsistent-
response,-which-limits-the-bandwidth-
and-accuracy.-Some-of-the-displayed-
measurements-are-wildly-wrong.-The-
Quad-is-great-for-casual-waveform-
viewing,-though,-especially-if-you-need-
to-see-multiple-signals.-It-even-includes-
a-crude-but-useful-function-generator-
that-outputs-sine,-square,-triangle,-and-
sawtooth-waves.
The-Quad-comes-with-two-analog-
probes-and-a-USB-cable-for-charging-its-
internal-lithium-ion-battery.-You-can-
download-a-manual-at-Seeedstudio.com.

Offered-through-RadioShack,-the-
Velleman HPS140i (2)-is-a-much-more-
straightforward,-finished-product.-
With-only-four-buttons,-it-is-easy-to-
use.-There-are-only-two-menus,-and-
functions-are-logically-grouped.-Some-
key-settings,-including-voltage-scale,-
time,-and-input-coupling,-don't-require-
the-menus-at-all.-The-sole-input-channel-
has-a-standard-BNC-connector-on-top-
of-the-case,-right-where-it-should-be-for-
handheld-operation.-A-rubber-shell-
protects-against-drops-and-bumps.
This-unit-has-an-unusually-wide-
and-very-readable-screen.-Available-
measurements-include-peak-to-peak,-
dBm-(decibels-referenced-to-one-
milliwatt),-and-Wrms-(weighted-root-
mean-square)-for-speaker-impedances-
from-2-to-32-ohms.-Clearly,-this-scope-is-
aimed-at-audio-work,-but-it-has-enough-
bandwidth-for-low--frequency-pulse-and-
RF-applications-too.-
The-HPS140i-has-one-fantastic-
feature-every-scope-should-include:-
fully-automatic-setup.-It's-the-scope-
equivalent-of-autoranging-on-a-digital-
spectrum.ieee.org

Randi silbeRman klett

1
http://www.Seeedstudio.com http://spectrum.ieee.org
Table of Contents for the Digital Edition of IEEE Spectrum March, 2012
