• Make 5V power supplies from surplus power adaptors

    2 days ago 0 comments

    If you are like me you will have accumulated surplus power adaptors for all kinds of things, modems, external hard disk drives, and so forth. Here's how to put them to use and avoid causing more 5V power adaptors to be made.

    5V has become a common standard for chargers and digital circuits. On eBay you can buy buck voltage converters that take 6-24V input and output 5V at 2A or more for about a dollar. As a bonus they have a USB A socket on the board ready to receive a USB cable. They are small, only a little longer than the USB socket. You just need to solder the input wires onto the board (double checking polarity first) and it's ready to use. Here's one powering a Raspberry Pi 1B.

    The primary current drawn depends on the input voltage and the output current. Assuming 90% conversion efficiency, the formula is:

    So for a current draw of 2A and an input voltage of 12V, the input current is just under 1A.

    One thing to be aware of: If you are using the input voltage for other purposes at the same time, the negative lines of the input and output are common, there is no isolation.

  • My experience using a PCB fab service (Pcbway)

    02/25/2019 at 14:00 1 comment

    When I counted a dozen 8085 CPUs in my retro tech stash, I decided to do a SBC project with them. The goals would be to learn to order PCBs online, and several other things. Coincidentally about this time a Pcbway rep contacted me asking if I would like to sample their service and post public feedback.

    The design I submitted is not mine, it's a completed 8085 SBC design published by Sergey Kiselev, see my project page for the links. This means I am confident that there are no mistakes in the placement and routing. It is not a complex design, only a handful of ICs due to the use of a GAL to replace a lot of discrete logic, two layers, 0.1 inch pitch ICs, and through hole components. One step at a time; I'll learn to use Kicad/pcbnew for my own designs later.

    A personal note: A PCB fab service over the Internet is something only dreamt of back in the days when I started making PCBs, first with resist pens, then later with photoresist, while dealing with noxious chemicals like ferric chloride and xylene. Well the Internet didn't even exist then. The disadvantage of course is the turnaround time so you should be fairly sure of your circuit before you commit to PCB. The old tailor's or carpenter's adage measure twice cut once is very apt here.

    Submitting the order through the website

    Like many fabs, registering an account on the Pcbway site will get you starter credit.

    At this point assume you have breadboarded and debugged your circuit, have laid out the PCB and are ready to generate the Gerber and drill files.

    The website is attractive and the steps are easy to follow. Just click on the Quote and Order button and it will take you through the steps. There are help buttons for the various entry fields. Pcbway seems to offer a great variety of options for the boards. I accepted the defaults as I have no special requirements. Maybe one day I'll design boards requiring advanced features. Like other fabs, the magical size 100x100 mm (from the limit of the free version of Eagle EDA, Kicad EDA is always free and has no limit) has special pricing, so usually people start with 5 or 10 boards within this limit.

    I noticed that Pcbway offers to upgrade you from HASL (Hot Air Solder Levelling) to the more expensive ENIG (Electroless Nickel Immersion Gold) at their discretion for no extra charge. This Pcbway page explains the two technologies. Searching on those acronyms will find you more explanations. You can veto giving them discretion if you wish.

    For Kicad 5 the documentation of pcbnew explains how to generate Gerber and drill files and can also be found in Pcbway's tutorial. For other EDA software there are abundant tutorials on the Internet. Package the generated files (usually 9) as a zip archive and upload to the website.

    At this point Pcbway will do a review of the files. Now I uploaded on a Sunday night so either they have software doing the checks, or there are reviewers working shifts which is plausible as a big fab like Pcbway must get a continuous stream of orders from all over the world, thanks to the Internet. In any case it was finished within an hour and...

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  • Things I want to learn, a wishlist

    02/02/2019 at 00:37 0 comments

    I hope to move things from this list to the one below.

    • Designing PCBs in Kicad
    • PIC MCUs
    • AVR MCUs
    • GALs
    • CPLDs
    • Use the nixies I have
    • SMD boards
    • Use up the retro components in my stash
    • Make things with the discarded technology I scavenged
    • ...
    • A robot that will do all the housework. I mean that would be the greatest step towards world peace. 😁

    Things I have done

    • Restored past projects in my junk box
    • Arduino
    • 8042/8048 MCUs
    • 8051 MCUs
    • TM1637 two wire interface
    • I2C
    • SPI
    • Various displays: LED, OLED, LCD, TFT screen
    • Rotary encoders
    • Kicad/eeschema
    • Small Device C Compiler
    • Ordering PCBs from a fab