Soon I come across a free software called “PWM Logic“. Supposedly it will turn Saleae Logic Analyzer into a PWM generator. An original Saleae Logic is somewhat too steep for my pocket right now. But I do have a cheap Chinese clone lying aroung. So I hook it up. Not surprisingly it does not work.

Knowing that Saleae Logic hardware is nothing but a Cypress CY68013A chip (that is why it is so easy to clone),  I decide to take a further step to reverse engineer the board and check why.

Some more googling leads me to the schematic of a cloned USBEE AX. USBEE AX is basically the same as Saleae except for two analog channels with limited function. On the schematic there is a 74LCV245 octal bus transceiver in between the testing terminals and CY68013A. The direction pin is connected to “DIR” net, but does not seems to link to anywhere else.

Tracing the board, the culprit is found immediately. On my Saleae clone, the 74245 direction pin is grounded, which means it can only receive signal from the terminals, not output to them. While examine the original Saleae teardown, there is no 74245 at all, the terminals are directly connected to CY68013A (with some schottky barrier, maybe). So the Chinese copycat actually did some “innovation” to include a buffer chip, for protection?

Since the reason is found, the next step is simple: break the 74245 direction pin and install a jumper to select input/output function.

Now I have a dual function Logic Analyzer / PWM Generator

P.S. CY68013A based logic analyzer is as good as its companion software does. Saleae have put a lot of efforts into its Logic software. Buying a clone and pirate the original software is not legal.

Update 28/09/2013: The PWM Logic homepage seems to be down at the moment. I have a local mirror here: PwmLogicSetup 1.0.1.3

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In the quest for alternatives I’ve tried Element14, RS Components, DigiKey, Robot-r-us, and some random ebay shops. All have their pros and cons. My personal favourite goes to China’s taobao.com. To those who are not familiar with Chinese B2C/C2C, this website is a Chinese fusion of amazon and ebay. There are millions of manufactures and private sellers setting up store front there. Virtually anything can be found, and usually without  minimal quantity. The only thing prevents overseas users from buying from taobao is you need a Chinese Alipay (copycat of paypal) account and a China mainland address. Obviously you must understand Chinese too to be able to browse the website and communicate with sellers. Dealextreme.com ventured into the communication gap. They collect orders and divert them to respective taobao suppliers, with a pretty decent margin, of course. In the early years SingPost has also looked into this market. They setup VPost, a concierge service which provides a virtual China address for delivery and then they forward to you using their SpeedPost service, at Fedex-alike charge. I used to use this often but feel too expensive for bulky items and usually I do not need the parts in a hurry.

With the huge influx of Chinese immigrants these years, other small concierge services pop up. And I finally found my playground… Oh sorry this is supposed to be a blog not a shopping guide. So today I collected my recent shipment from 65daigou.com. Here is a partial list:

ATTEN AT8586 2-in-1 SMD rework station with TONS of freebies at RMB275 (S$57). I used to have an AOYUE 8032A portable hot air gun but it has serious heat controlling problem. I hesitated between AT8586 and AT858D (as recommended by EEVBlog, again), and finally choose AT8586 because it is more compact for my limited work space. Although I’m not a fan of ATTEN brand due to the incident of their reckless copying of Rigol digital scope, their soldering equipment seems to be pretty decent quality among Chinese products.

A LCD bracket at RMB109 (S$21.8). As I mentioned in previous blog I’m not totally satisfied with the iPad clip. The flex arm is too stiff to be bent into the shape I wanted. So I get this LCD wall mount bracket. After some modifications I’m able to mount the iPad clip onto the ball head and now I have a super steady iPad mounting solution.

Some SMSC USB2514 chips at RMB10 (S$2) each to repair the USB hub on my Dell U2211 monitor.

100 pieces PCB heat transfer paper at RMB30 (S$6).

6000x50mm cooper plated kapton tape for making flex PCB, at RMB25 (S$5).

Some small USB connectors, at RMB0.2 (S$0.04) each.

A set of small spudger tools, two rolls of Kapton tape and some solder mask oil at RMB62.5 (S$12.5).

Everything weights up to 6.5KG, and I paid S$127 for the products, S$13 for agent fee and S$26 for shipping by sea. It only takes 1 week to reach Singapore, same as normal airmail (woot!)

So next time I know where to shop.

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