• Padauk "3¢ MCU" resources

    8 hours ago 0 comments

    I've been reading about these "3¢ MCUs" and thought I'd publish the links I have.

    The "terrible" 3 cent MCU. Padauk's products are on this list.

    An in-depth look at the Padauk line and the Hackaday writeup with links to example projects. The 3¢ MCU is a SOP8 OTP part with offline programming, the MTP parts are several times more. So you would normally simulate it first. And if you make a mistake, well it's only 3¢.

    An early exploratory project and the Hackaday writeup.

    The Padauk product page. The OTP PMS150C is the low end of the line and the one most discussed. You can also drill down to find the Padauk IDE download (quite lightweight) for Windows (even XP) and even runs under Wine on Linux. This interfaces to Padauk's ICE and programmer, for which the open toolchain project below is trying to create substitutes.

    The epic EEVblog thread discussing reverse engineering the MCU and creating a free programmer and toolchain.

    The Github Free PDK "organisation" with many projects: software tools, open programmer hardware and software, MCU instruction set documentation, code examples, SDCC code examples, and more. As of Feb 2020, I don't know of any ready made programmer for sale yet.

    Small Device C Compiler from 3.9 onwards has support for the Padauk MCUs.

    You won't find Padauk's products on eBay. You can buy them from LCSC (with minimum order surcharge and shipping costs so you'd have to make a large purchase to make it worthwhile), and here's a deep link to Padauk products; or some Aliexpress vendors with considerable markup.

  • A review of Ocean Smile (formerly LocoPCB) PCB service

    12/04/2019 at 23:34 0 comments

    Update 2020-01-15: Got email from them saying they have merged with Ocean Smile (who thinks up of these names?) with a new site. As far as I can tell the pricing structure is unchanged and my old account works so my next 4 5-board orders are still $2.

    The story is finished: LocoPCB was offering 5 100x100 mm boards for $2 + shipping. Gerber files were uploaded and after one to and fro with the customer rep, it was sent to processing and then manufacture. I misunderstood the difference between those two stages, read the Order Status section below. It was shipped. I received the board just before the new year and I reviewed the quality below as well as the V-cut feature.

    Ocean Smile PCB

    I saw ads from LocoPCBOcean Smile on PCBShopper many times and when I saw that they were offering 5 100x100 mm boards for $2 + shipping I decided to give them a try because they offered V-cut panelisation for free. Their office is in Shenzhen but the factory is in inland Guangzhou.

    The loco referred to locomotive as you can see from their logo. I wonder how people react to the name in Spanish speaking countries. I suppose it's still publicity.


    The board is actually under 100x48 mm so I made 2 panels per board by using the Append PCB operation in pcbnew, then adjusted the outline (Edge Cut). V-cuts must be from edge to edge. Both top and bottom of the PCB are scored, leaving about 1/3 FR4 material. Should be interesting to see how hard it is to separate the halves compared to breaktabs and mousebites.

    To ask for V-cuts in the form you tick the Customer Panel option, and the V-cut should be an edge to edge line in the Edge Cuts layer. This confuses the 3D viewer once added, as the outline is no longer a closed polygon, so you will not be able to view the board outline there, though the rest can be viewed. One complication is that I wanted to preserve the rounded corners so I had to leave 2 mm bays so that the router could cut that. Here's what the board looks like:


    While consulting their support pages for requirements I found that the images wouldn't display in Chrome. The reason is that the page are served by https but the images are served by http. Chrome considers this insecure. Firefox will display it with a warning in the location bar. I sent a bug report to their IT department. (2020-01-01: Their order pages have been under refurbishment since mid-December, hopefully fixing the http/https problem.)

    Like other fabs you fill in the form and upload the Gerber archive. You have to pay (Paypal or Visa) before it is checked.

    I had noted that unlike many other fabs they want PTH (Plated Through Hole) and NPTH (Non-PTH) in one file. This is an output option in Kicad/pcbnew. But I had failed to note that Include Extended (X2) Attributes should not be selected. And Protel file extensions of course. Must be older software that they are using. As a result, the customer rep asked me to resubmit. The redone archive worked. So to summarise:

    • Protel file extensions
    • Enable PTH and MPTH in a single file
    • Disable Include Extended (X2) Attributes

    Order tracking

    Each account has a page for tracking orders, Naturally I had only one order in the table. The usual details are shown. Some of the GUI elements like View Detail and Invoice can be clicked on, some show popup windows when moused over, such as Ship To. The Tracking element becomes live when tracking information is available. But since it's obtained from the carrier, some lines are in Chinese and you will need a translator if you don't read Chinese and are really interested in where your package is.

    Order status

    First the status showed processing. I thought this meant it was being made, but it turns out that this is probably just the stage where they prepare the design material such as files to drive the machinery.  It stayed in this stage for 3 days.

    After that it went into manufacturing. This should be where they actually make the board, i.e. the chemical...

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  • A review of 3 electronics bazaars in China

    11/18/2019 at 13:36 0 comments


    2020-01-31 Aliexpress/Warranty: Personal experience successfully getting a refund.

    2019-12-23 Aliexpress/Shipping: Some Aliexpress stores will allow you to combine shipping for multiple items.

    2019-12-06: Added a placeholder section for Banggood.

    2019-12-04: Aliexpress/Shipping: Aliexpress uses a single number for orders combining > 1 seller.

    2019-12-01: LCSC/Specifications: Symbols and footprints for Kicad can be obtained from the LCSC product pages. Explain how to extract information.


    First of all let me define the topic of review. By electronics I mean things that makers use, for example active components like chips, as well as passive components like resistors, electromechanical and optical devices, as well preconstructed modules like MCU platforms. But I exclude consumer electronics like phones. I also include materials and tools for working with electronics, like heat shrink tubing, soldering stations, multimeters, and so forth. Services like PCB manufacturing and assembly are also found in these bazaars. For these sites if you search under electronics, you end up seeing phones and that sort of thing. Usually it's the industrial category you want.

    Next, the caveats:

    • My assessment is individual. I am a hobbyist and just want to get adequate quality materials at acceptable cost. Projects that have more stringent requirements will have to do more homework. I can write about only my experiences. Feel free to comment and add your experience.
    • The situation varies a lot depending on where you live, payment methods, shipping costs, customs procedures, import duties, shipping times and so forth. I can write about only my situation, be sure to check yours. Again feel free to contribute.
    • The situation varies by time too, exchange rates go up and down, special sales may benefit you.
    • These are not the only 3 sources for electronics from China, there are many others. I may extend my review in future.
    • China is not the only place to buy components, but probably is the largest source. Also you may prefer to patronise a local shop for one reason or another, e.g. quick delivery or consumer protection laws.

    The three sites I review are eBay, Aliexpress and LCSC. The first two are seller platforms that host many shops while the third is a major component supplier to the trade and makers.


    Usually this is the first place people head for as it's well known. Chinese sellers are well-represented here. They are usually based in Shenzhen, Shanghai and other coastal cities. Some have operations in Hong Kong. A few are found inland. But it really doesn't matter, for more than the obvious reasons.

    Choice: You will be spoilt for choice. Competition is cutthroat and prices often differ by a few cents. Besides price I also look at how many stars the shop has acquired, and the rating. I also tend to prefer shops that specialise in the kind of stuff I'm looking for. To some extent this is self-adjusting; you are less likely to see a home lighting shop sell Arduino workalikes, but they may sell bulk bags of LEDs. However the caveat is choice is good only for items in demand. The sellers here don't like holding inventory that doesn't move quickly. If you want that specialised chip you will need to go to a well-equipped stockist.

    Specifications: One problem with listings is that it's often difficult to work out exactly what you are getting. Does that WiFi dongle have a Linux driver? You may have to look through several similar listings before you see mention of the chip used which you can then go check for compatibility. This sort of research is time-consuming, sometimes a little enjoyable, but it comes with the territory.

    Price: eBay allows you to sort by price+postage lowest first. However many shops counter with the trick of advertising several items in one listing, and it turns out the cheapest price is for some related item. For example an Arduino board listed for $1 may...

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