Review of the Wittig / Welec W2022A Digital Oscilloscope (July 2009)
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Quick summary: potentially a great value, but lousy factory firmware renders it barely usable.
The new beta replacement firmware is a good add-on, and makes the device worthwhile.
Late July-2008: Scope source code now available.
There are two very active groups currently working on reverse engineering
these scopes, with a view towards producing better firmware for it someday.
One Russian forum is very
busy analyzing the hardware and FPGA components (and their site defies any attempt
at auto-translation by Google/Babelfish, but one can translate it the hard way
using cut/paste of text into the translators). They seem to believe that the scope
should be capable of around 60 refreshes/second, instead of the current 2-10 refreshes/second.
Meanwhile, a German group has actually
managed to get the Wittig brothers to release (most) source code for the scope,
and the code is now available on SourceForge.net.
But this is still missing a rather important hardware description component,
so it cannot be used or recompiled yet. The C++ code looks like it was written by a 10-year old
with a TRS-80 BASIC programming background. Ugly and unreadable as hell, with little hope of
being salvageable.
25-July-2008: Firmware v1.3 was released.
The only reported change from v1.2 is that the PC software connection (broken by v1.2) was apparently fixed.
The User Guide has also been updated, and is much smaller than before,
reflecting the removal of documentation for features that don't actually exist.
The remainder of this review is still (for now) based upon the original March 2008 firmware.
I have not yet taken time to perform an in-depth re-review,
so some of the bugs described below may no longer be present,
and there may be new bugs not yet listed.
14-July-2008: Firmware v1.2 was released.
I have downloaded and installed the update, and some differences are immediately obvious:
The vertical gridlines are now correctly drawn with five (5) sub-divisions per division (yay!).
The FFT menu item has been completely disabled (ho-hum).
Scrolling through captured traces appears to work more often than before,
though it is still painfully slow.
The PC/Windows software now completely fails to communicate with the scope (yawn).
The Good
For less than US$600/EU400 new/delivered
(eBay),
with two quite decent 200Mhz probes included,
this ultra-compact scope boasts of +/- 3% vertical accuracy, 1 billion samples/sec, and 200Mhz analog bandwidth.
It has cushy silicone buttons, some with coloured backlights to indicate current status,
well laid out controls, and a potentially great soft button menu system.
There is also a USB 1.1 interface, and a serial port.
It powers up into a usable state in under 15 seconds or so,
and can even manage a passible 3 frames/second (acceptable for a storage scope) on the
YouScope Demo.
The controls layout is a near exact clone of the Aligent DSO6012A, which costs around $5000 in a typical configuration.
But beauty is only skin deep in the $600 Welec knock-off of it.
The Bad
It seems to have an inherent noise floor of perhaps +/- 3-6% on many signals,
depending on the volts/div setting. This, combined with firmware bugs in virtually every
single aspect of its operation, make for a somewhat dicey purchase.
There are a lot of bugs. Pretty much every button and function seems
to have at least one noticeable bug, and some measurements look off.
The highly touted "16KB/channel" buffer (really only 4KB in many modes) is useless, because one cannot navigate through it in a captured trace
(see scrolling bugs below).
The unit I received has two hot pixels on the display,
one of which is visible in the photograph above if you look hard enough
(second grid from bottom, fourth grid from left).
The company (just three guys as far as I can tell), does release firmware updates
every few months or so, but most of the bugs listed below have been around
for at least the past year. So don't count on anything ever being fixed.
Eric Wittig is apparently responsible for some of the software.
Michael Wittig (sales dude) and Thomas M. Wittig (hardware, firmware) did respond
to a couple of my early emails, but nothing was fixed.
They stopped conversing as soon as the 14-day return window slammed shut.
Not that they might have honoured the return window anyway,
or at least that's what other users have suggested (see the German discussion threads linked below).
And besides, numerous flaws and all, I'm keeping this scope.
Returning it to Germany would be too risky/expensive for me.
Bugs Observed in Firmware Version 1.10.03 (25-March-2008):
The vertical grid lines are drawn incorrectly, showing 6 sub-divisions per division,
rather than the intended 5 sub-divisions. This makes reading any kind of
measurements from the display rather difficult, as most of us are not
used to base-6 arithmetic.
Quick Meas voltage measurements do not appear to match the onscreen waveforms.
This could be related to the base-6 arithmetic bug above.
Average Voltage appears to actually show average peak voltage,
which is high by about another 3% (beyond the +/- 3% quoted accuracy)
due to the inherent noise levels of the scope.
The horizontal zoom knob function is flaky when viewing captured traces.
Sometimes it works, sometimes not.
When horizontal zoom does function (a rare event), it is usually only good
for two or three zoom levels.
When using horizontal zoom, the display seems to jump scroll horizontally
to a random point of the captured trace. This random point changes with each
level of zoom.
The horizontal scroll knob often does not work at all on captured traces,
making the 4KB/16KB trace buffers rather redundant.
When it does work, horizontal scrolling is way too slow to be usable.
The vertical zoom knob functions only when the scope is in continuous capture mode ("Run" mode).
Captured traces can only be viewed at the vertical resolution from the time of capture.
Zooming in/out is not possible at all.
The controls sometimes lock up and the scope stops capturing traces.
Pressing either the Power button or the Auto-Scale button
appears to be the only way to escape this mode.
The Run/Stop button normally shows green for Run, and red for Stop.
But sometimes it shows green while stopped.
After exiting Quick Meas, the soft key menus still show Quick Meas menus.
This happens for other functions, as well.
Power on zero drift. If you turn on the unit and observe the zero level, you may notice that it drifts quite a bit over time - probably due to the lack of thermal compensation.
Occasionally, the trigger will lose sync and you need to stop and start the capture again for it to re-acquire the trigger.
The video triggering doesn't work at all.
Many more minor bugs, not yet listed here.
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The Ugly
There are several noticeable differences between claimed capabilities
and actual implemented functionality. Someday, somebody is going to sue these folks into
bankruptcy -- oh, wait, that already happened once, which could be why they
changed the company name. :)
Missing Features that are Claimed to be Present:
The documented feature to trigger on individual video scan lines is missing from the product.
The Horizontal Roll function, described in the manual, is not implemented.
Missing advanced (aka. "useful") FFT functionality:
Pages 5-22 through 5-25 of the User's Guide describe a comprehensive set of FFT
(Fast Fourier Transform) controls and menus. The illustrations there show menu
entries for Span, Center, Preset, More FFT, Scale
and Offset. Additional mention is made of interactions between FFT and the
Quick Meas menus.
These imaginary functions/menus simply do not exist in the shipping product.
The only FFT function in the product is a simple frequency overlay plot,
which also slows the scope down to one screen refresh every 2-3 seconds or so.
There are no scale/units labeled on the simple FFT plot, which makes it nearly 100% useless.
Poorly Implemented Controls:
When it works (not often), the horizontal scroll knob is too tiny, too clicky, and way too slow.
The vertical scroll knob is also too tiny, too clicky, and even slower than the poor horizontal knob.
The Quick Meas functions slow the screen refresh down to about 1/5 normal speed.
The useless FFT function slows the screen refresh down to about 1/30 normal speed.
The Probe Comp ouput contact is some kind of funky fragile gold plated recessed fitting,
rather than the usual probe-friendly clippable tab. It is very difficult to hold the probe
onto this signal while manipulating the scope controls. What were they thinking?
The vertical sensitivity/resolution is implemented as three ranges of three voltage levels
each (with 1:1 probes, these are 5,2,1V, 500,200,100mV, and 50,20,10mV).
A mechanical relay goes *click* when switching across ranges, presumably as a cost
saving measure. The best accuracy and lowest noise is on the highest voltage level
of each range (5V, 500mV, 50mV). The other levels within each range suffer
from considerably higher noise levels.
The included probes are of very good quality.
But there are no instructions on how to use the three separate adjustments on them.
Windows Software Application:
The scope includes a basic MS-Windows-only software application
which communicates over USB. This application provides remote control
of the scope from the PC, and can be used to print trace captures
from the scope.
But just like the firmware, this application is also riddled with bugs.
Live display viewing doesn't work for me here, so that ruins any concept of remote control.
And printed screen captures do not have grid lines, which makes them similarly useless.
Prints are also abruptly cut off at the page bottom for some reason.
The software randomly stops working at times,
requiring the USB cable to be removed and reinserted to regain communications
(or maybe that's just a general Windows thing).
Relevant Links:
SourceForge Site for Welec W2000a
The original Google-Groups site
Discussion of scope internals (Russian). (Neither google nor babelfish correctly translate this site. Sad.)
Best discussion of scope internals and current software development (German/English).
Source code, now compiles!.
eBay Link to seller's current items.
My YouTube video demo of the scope.
YouTube: aliasing issues.
YouTube comparison with other brands.
YouTube: Ringing on W2000A (fixable someday, but only with new VHDL).
Similar site from a German reviewer.
EmpegBBS Discussion thread.
mikrocontroller.net thread about the Wittig/Welec scopes>
mikrocontroller.net thread about developing a Linux USB interface (using Qt) to the scope
(english translation here)
progforum.com review thread
(english translation here)
Welec Company Web Site.
April Fools Day Joke Announcement (do NOT believe it!).
A Note From Another Purchaser
After this site went up, I received email from someone else
who had purchased, and successfully returned, a scope for full refund:
"Welec, is the same company previously called Wittig Electronics that went
bankrupt. I purchased a W2012 (note no "A") that looks identical. it was a
POS. I use PayPal for eBay purchases, and was able to get refund. Perhaps
you can too. These guys are very shady. I'm not sure how they get such high
ratings on eBay, they must be gaming the system. I ended up buying a used
Tek DSO on eBay, and I'm satisfied."
