Using Cheap Asian Electronic Modules by Jim Rowe
USB Logic
Analysers
This 8-channel USB logic analyser is essentially a clone of the original
version of the well-known and respected Saleae Logic unit. It’s
completely compatible with the Saleae design, but you can get this
one for as little as £8 – less than one-fortieth the cost!
S
ome of you may be familiar
with the range of Saleae USB
Logic Analysers. Although most
models only have eight channels, on
the whole, they are excellent performers and probably suitable for 95% of
the analysis work done by hobbyists,
technicians and designers.
They start from several hundred
pounds – not nothing, but still only a
fraction of the cost of getting a ‘professional’ logic analyser, which makes it
an attractive purchase – particularly
since Saleae allow you to download
the matching control and analysis
software for free.
I bought an early 24 megasamples
per second (MS/s) eight-channel ‘Logic’
model, and when Saleae brought out
a 16-channel version, I bought one of
those too. And I’ve been very happy
with them both, especially as Saleae
has kept their software up to date.
But recently, USB logic analysers
like the original Saleae Logic began
to appear on the world market, at a
much lower cost. They all seem to be
made in China, and many of them are
virtual ‘clones’ of the original Saleae
Logic. They’re all 8-channel units with
a maximum sampling rate of 24MS/s,
and in most cases, they work exactly
the same as the Saleae Logic when
hooked up to your PC.
Even Saleae’s software can’t tell the
difference. What was that old saying
about, ‘imitation being the sincerest
form of flattery’? However, Saleae’s
‘Terms of Service’ says that you may
not use their software with unauthorised clones of their products (www.
saleae.com/terms-of-service). But
there is a alternative, which we’ll get
to a bit later.
At the time of writing, there are
quite a few of these Saleae Logic clones
available on various online sites, at
prices varying between £6 and £20
depending on the supplier and their
location. Sources include Banggood
in China, Sparkfun in the US, Sparkfun’s suppliers in the UK and quite a
few others you can find on eBay (item
174534651401) and AliExpress
I should point out that Saleae no
longer makes the original 8-channel 24MS/s logic analyser, the one I
bought. Instead, they offer the Logic
8, which samples at up to 100MS/s,
priced at £299 direct from Saleae in
the US (www.saleae.com). They also
offer the Logic Pro 8, which provides
500MS/s sampling (£529). Plus they
sell the Logic Pro 16, offering 500MS/s
sampling of 16 channels (£749). (The
above prices are plus VAT and shipping). So Saleae has moved up-market,
leaving the lower end to the clones.
Cheapest and most popular
Unsurprisingly, the most popular of
these clone logic analysers is one of
the cheapest. It’s available from Banggood for approximately £8 (Banggood
1177821; https://bit.ly/pe-feb21-bg).
Inside the logic analyser (shown enlarged for clarity), we found a board
with a 56-pin Cypress Semiconductor USB-capable micro, a 24C02 EEPROM,
octal bus transceiver chip, regulator, crystal, transistor, two LEDs and a handful of passive
components. The bus transceiver operates as a level shifter and also protects the micro inputs.
Practical Electronics | February | 2021
39
For comparison, here’s the original Saleae Logic, purchased a few years ago,
along with the supplied (functional!) USB cable and high-quality test clips.
This includes a USB type-A to mini
type-B cable (the analysers are powered via the USB cable) and a set of 10
ribbon cable test leads, with female pin
sockets at each end.
The US$19.95 Sparkfun clone appears to be identical (www.sparkfun.
com/products/15033), apart from a
more attractive label on the top.
This device is housed in a plastic
box measuring 55 × 27 × 14mm, which
appears slightly smaller than the original Saleae Logic unit. That came in a
nicely finished machined metal box
measuring 41 × 41 × 8.5mm. Apart
from this, the main physical difference
is that the cheap unit has a 10-pin DIL
connector for the test leads, whereas
the original Saleae Logic had a 9-pin
SIL connector.
Another difference is that, while
the original Logic (and the later Saleae
models) came with a set of nine high-
quality E-Z-Hook Micro test clips, the
clone units just come with female-tofemale ribbon cable leads. If you want
test clips, you have to buy them separately – more about this a little later.
Finally, whereas the original Saleae
Logic (and later versions) came with a
sturdy little storage case for itself, its
USB cable, test leads and clips, the
clones come without a case.
Electrically, the clones seem to
be virtually identical to the original
Saleae Logic. When you connect them
up to a USB port of a PC, they are recognised as a Saleae unit. And if you
fire up Saleae’s software, it behaves in
precisely the same way as it does with
a genuine Logic (but you’re not really
allowed to do that...)
Alternative software
If – like me – you’re not willing to
violate Saleae’s terms of use and use
An end-on view of the clone logic analyser showing
its 10-pin DIL box header and the supplied USB
cable, which was missing a pin.
40
their software with one of these clone
units, there is an alternative.
The open-source software website
http://sigrok.org has a software package for download called PulseView.
This comes in three versions, to suit
Windows, Linux and macOS.
For PulseView to be installed on a
Windows machine (XP or later), the
WinUSB driver must already be installed. If this isn’t already installed,
you can install it using software called
Zadig (http://zadig.akeo.ie/), which
we have used in the past for driver
installation (eg, in the Banggood SDR
kit, reviewed in PE, November 2018).
I downloaded and installed PulseView, and found using it to be quite
similar to the Saleae software in operation. You can also download a 24-page
PDF user manual from the sigrok website, to help you figure out how to use
it (https://sigrok.org/doc/pulseview/
unstable/manual.html).
PulseView worked equally well
with both the Saleae Logic and the
clone, and offers an even larger range
of protocol analyser options (54 in all),
including all the popular ones like I2C,
SPI, UART, CAN, I2S, 1-wire, S/PDIF,
HDMI CEC, JTAG, MIDI, PS/2 Keyboard/Mouse, USB LS/FS, RGB LED
(WS281x) and PWM.
Most importantly, there is no limitation on using PulseView with the clone
logic analysers! That, and the fact that
it has more features, makes PulseView
the way to go.
You can see a typical display from
the PulseView software in Screen 1,
which again shows the SPI signals
on one of my Arduino-based Audio
Millivoltmeter prototypes (PE, October 2020).
As this software works with both
the original Logic and the clones (as
shown in Screen 2), I was able to make
a direct comparison when analysing
The genuine E-Z-Hook test clips,
shown at right, are much easier to use
and more reliable than the cheap test
hooks I initially purchased, at left.
I eventually found a much betterlooking set of low-cost test clips at
Banggood (see text).
Practical Electronics | February | 2021
Screen 1: the free PulseView software working with a clone logic analyser to decode
SPI serial data. It’s easy to use and can decode many different digital protocols.
both I2C and SPI signals on one of the
prototypes of my Audio Millivoltmeter. I’m glad to report that the results
were identical.
Sparkfun have a short tutorial on
using their USB logic analyser with
PulseView at: https://bit.ly/pe-feb21-sf
USB cables and test clips
I ordered two of these low-cost analysers to check them out for this review,
and when they arrived, I tried connecting them to a PC using the supplied
USB cables. But neither of them were
identified by Windows when plugged
in. It was only when I tried using another, known-good USB cable that they
sprang into life.
When I looked inside the type-B
mini plugs on the end of the supplied
cables, they were both missing the pin
4 contact! Presumably, that’s why the
analysers wouldn’t work with those
cables. That was a bit disappointing,
but luckily this type of cable is readily
available for only a few dollars (and
you’re likely to have a few already, as
they’re pretty common).
As mentioned earlier, these ultralow-cost USB logic analysers don’t
come with any test clips – just a set of
female-to-female ribbon cable leads. So
unless you’re only going to be testing
signals already routed to pin headers,
you will need a set of test clips as well.
The E-Z-Hook XKM-S micro test
clips originally supplied by Saleae
are available separately, but at a fairly
steep price. For example, you can buy
a set of 10 from Digi-key (461-1012ND), but they’ll set you back about
£20 plus shipping. This doesn’t seem
all that attractive, since it’s around
three times the price of the USB logic
analyser itself!
I found some likely-looking sets of
10 ribbon cable leads with micro hook
test clips on eBay for just over £3, so
I ordered a couple of them. But when
they arrived, I found that the micro
hook test clips were not nearly as well
made as the genuine E-Z-Hook clips.
The female connector on the end
of the lead would not attach securely
to the pin at the back of the clip, and
the hook tips didn’t seem to have the
right shape to mesh properly and attach securely to an IC pin.
So it was ‘back to the drawing board’
– or more accurately, back to the web.
On the Banggood website, I found sets
of ‘logic analyser test leads with hook
clips’ that looked more promising.
These have the lead wires soldered
to the rear of the hook metalwork inside the plastic housing, removing the
problem of connecting the clips reliably
to the leads (Banggood 956251; https://
bit.ly/pe-feb21-bg2). These sets of leads
cost just over £5 for 12, or £7.50 for 20.
If you don’t want to invest in a set of
genuine E-Z-Hook clips, these would
be a good alternative.
Reproduced by arrangement with
SILICON CHIP magazine 2021.
www.siliconchip.com.au
Screen 2: the official Saleae logic software operating with one of their logic analysers to decode the same bus as shown
in Screen 1, although there’s slightly different data this time. While there are some visual differences, the two pieces of
software work similarly.
Practical Electronics | February | 2021
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