Fullscreen HTML5Med Res (??MB)HTML4

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 A$12.40 – less than one-tenth the cost! I n the September 2009 issue, we published a review of the then-new Saleae USB Logic Analyser, written by Geoff Graham (siliconchip.com.au/Article/1558). Although Geoff pointed out a few limitations (like only having eight channels), on the whole, he found it an excellent little performer. He wrote that it was probably suitable for 95% of the analysis work done by hobbyists, technicians and designers. In 2009, you could buy the original Logic direct from Saleae (www. saleae.com/) in the USA for US $149 plus delivery, which ended up being about AU $250. This was still only a fraction of the previous cost of getting a ‘professional’ logic analyser, which made it an attractive purchase – particularly since Saleae allowed you to download the matching control and analysis software for free. Prompted by Geoff’s review, I bought one myself. Then 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 24 Megasamples per second (MS/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, their “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 $12 and $36 depending on the supplier and their location. Sources include Banggood in China, Sparkfun 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. siliconchip.com.au Australia’s electronics magazine February 2020  75 For comparison, here is the original Saleae Logic unit which I purchased a few years ago, along with the supplied (functional!) USB cable and high-quality test clips. in the USA, Sparkfun’s supplier Core Electronics in Australia and quite a few others you can find on eBay and AliExpress (www.ebay.com.au/ itm/193121890194). I should point out that Saleae no longer makes the original 8-channel 24MS/s logic analyser. Instead, they offer the Logic 8, which samples at up to 100MS/s (priced at $639) and the Logic Pro 8, which offers 500MS/s sampling ($1119). They also sell the Logic Pro 16, offering 500MS/s sampling of 16 channels. So Saleae has moved up-market, leaving the lower end to the clones. Cheapest & most popular Unsurprisingly, the most popular of these clone logic analysers is the cheapest one. It’s available from Banggood for approximately $12 (Banggood 1177821; siliconchip.com.au/link/ aax7). 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. 76 Silicon Chip The clone from Sparkfun for US $19.95 appears to be identical (www. sparkfun.com/products/15033), apart from a more attractive label on the top, as is the one which Core Electronics sells for just over $35 plus delivery (siliconchip.com.au/link/aax8). This device is housed in a plastic box measuring 55 x 27 x 14mm, which appears slightly smaller than the original Saleae Logic unit. That came in a nicely finished machined metal box measuring 41 x 41 x 8.5mm. Apart from this, the main physical difference is that the ‘el cheapo’ 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 highquality 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 Australia’s electronics magazine 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 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, macOS etc. 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 this using software siliconchip.com.au Screen 1: the free PulseView software working with one of the ‘el cheapo’ clone logic analysers to decode SPI serial data. It’s easy to use and can decode a great many different digital protocols. 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. siliconchip.com.au Australia’s electronics magazine February 2020  77 called Zadig (http://zadig.akeo.ie/), which we have used in the past for driver installation (eg, in the Banggood SDR kit, reviewed in November 2017; siliconchip.com.au/Article/10879). 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 (October 2019; siliconchip.com.au/Article/12018). 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 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 siliconchip.com.au/ link/aaxa USB cables and test clips 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. 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 $40 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 $6, so I ordered a couple of them. But when they arrived, I found that the micro hook test clips were not nearly as well 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 better-looking set of low-cost test clips at Banggood (see text). 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 78 Silicon Chip 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; siliconchip.com.au/link/aaxb). These sets of leads were priced at just over $7 for 12, or over $11 for 20. So if you don’t want to invest in a set of genuine E-Z-Hook clips, these would probably be your best alternative. You can also try Jaycar Cat HM3037 for SC $1.75 each. Australia’s electronics magazine siliconchip.com.au