tinyK20: New Board with micro-SD Card

Thanks for all the feedback and suggestions so far on the tinyK20 project! I’m proud to present the next iteration of the universal microcontroller & debugger board based on the Freescale Kinetis K20 USB microcontroller:

tinyK20 Board

tinyK20 Board

Changes from the earlier version (see “tinyK20 Open Source ARM Debug/Universal Board – First Prototypes“):

  1. Replaced the K20 crystal with one having a smaller footprint.
  2. Added Micro SD card socket on the back (same socket as on the FRDM-K64F or FRDM-K22F).
  3. Because SD cards can draw more than the 120 mA the K20 internal 3.3V provided, there is a footprint on the backside of the board to add an extra DC-DC converter.
  4. Moved reset button and headers.
  5. First version with transparent enclosure.
tinyK20 Thumb Drive Version

tinyK20 ‘Thumb’ Drive Version with transparaent Enclosure

USB Cable Version

tinyK20 ‘Cable’ Version

The new version includes a micro-SD card socket on the bottom side of the board. Because the 3.3V DC-DC converter of the K20 only can drive 120 mA, there is a footprint on the back to add a 5-to-3.3V DC-DC converter.

tinyK20 Thumb Drive Bottom side

tinyK20 Thumb Drive Bottom side

tinyK20 with SD Card Inserted

tinyK20 ‘cable’ version with SD Card inserted

If the breakable debug part of the board is removed, the SD card can be easily removed. But it works well with the ‘full’ board, but of course is not that user-friendly.

One thing we will probably do for the first ‘production’ run is to move the capacitor under the SD card. Personally, I prefer the ‘USB cable’ version: I have a mini-USB cable already, that makes it easier to move the board, say to the robot to be programmed, as the SWD flat cable should be only a few centimeters long. My vision is to use a transparent shrink-tubing around the board instead of a special case. What do you think? Which version would you prefer: the ‘cable’ or the ‘thumb’ version?

Happy tinying πŸ™‚



36 thoughts on “tinyK20: New Board with micro-SD Card

  1. Hi Erich!
    Nice one project! For me cable version is more universal. As i can see it is doublesided project. Ho did you make layers interconnection?


    • Hi Alexey,
      yes, it is a dual layer board. The vias/interconnections are done outside the university. They put a materil into the holes, and then transform it in a bath to cupper connections.


  2. Hi Erich

    Cable version +1

    Is it practical to add an option to connect a serial port to the target board in the way that the FRDM boards do? Then your new board could act as a console to the target board while developing. Even if you leave the software till later.

    Can the target be powered from this board? e.g. using the optional regulator?

    AFAIK the schematics in GitHub must be for an earlier version.

    FYI I have been using this connector for SWD, power and UART on my targets – it is small and low profile and surprisingly robust. tinyurl.com/oyk5kbd If it was my design, I’d add one to the K20 board – I’ll provide pinouts if you like, and we can set the new standard πŸ˜‰


    • Thanks for voting πŸ™‚
      About that serial port: you mean to use the board as UART(3.3v)-to-USB CDC bridge? Yes, absolutely. Same functionality as the FRDM board do.
      The 3.3V are provided on the SWD connector, but this is not intended to power lots of current. Of depends on the optional regulator.
      Schematics: yes, I had no time to update the files yet. About that connector: so this is what you put on your boards as debug and serial port? So you build a SWD-to-ThisConnector in order to debug the board? My current thinking is that the normal SWD connector (5×2 pins) is more of the standard, and if I want serial over it, I could use e.g. the Segger Realtime terminal functionality instead?


    • Hello,

      Very nice project. And it’s awesome you are releasing the source files. Do you also plan to release the gerber files so one can make the boards at home or using an online fab service ?

      I would be really interested to try to make a small batch, eventhough it’s still a prototype.

      Cable version is easier to use on desktop (most common use), but having an USB-stick version is easier when travelling. If you could keep both footprints, that would be great.

      Thanks you also for all the posts on this blog, they’re really helpful


      • We plan to produce an initial batch of 50 boards populated with the components, with solder-stop mask, etc. The project is made with Eagle, so the plan is to share the Eagle files so everyone could make his own board.
        It could be interesting to produce a higher amount of boards (maybe after the 50 initial ones), if there is enough demand. But not sure if there will be enough demand?


  3. I prefer cable version ! πŸ˜€ .

    I will surely buy more then one if you go in production . Do you have an idea when it will be release ?


  4. At the risk of becoming boring – if you’re doing another PCB iteration, why not hook up a K20 UART to the 10-way connector pins 6 and 8, through series resistors so you can choose whether to use this functionality or not…


      • Hi Charles,
        here is what we are looking into: adding two vias/holes on the detachable programming PCB part, connected to SWD pins 6 and 8 (or could other pins be used?). Then you can connect yourself these vias with two wires to the UART RX/TX of the K20 which are available on the two outer side rows of the board. That way you can connect/debug your own target board with the Rx/Tx lines from your target board routed to the K20. Would that work for you?


  5. Hi Erich,

    Nice tight design! +1 cable version.

    I have not looked at the IO logistics, but it would be optimal if you could use 1 2×5 SWD as dual pupose, self debugging – target debugging. Looking at the schematics, it appears that the same SWDIO, SWCLK are used in both cases.

    Very nice addition of the uart to debug header.

    I have been using freedom boards as an mbed loader for my custom boards using the SWD connector. Perhaps if you added some marketing to this project with mention of mbed, it could increase your order volume?

    You never know what might happen with a kicstarter as well – could be a hit!

    Nice work.


    • Thanks πŸ™‚
      As for a dual-use SWD connector: yes, we looked at that one, but this was really hard to get implemented, especially with a dual layer board. At the end it was simpler and cheaper simply to ask that second connector on the board.


  6. Hi Erick, Nice work!
    I missed this FTF2015 and the chance to see you there, but maybe next year.
    I tried to avoid this package during prototyping but size is really attractive, Are you soldering the K20 by hand? I guess this is the first component to mount..


    • Yes, soldered by hand. It is actually not that hard if you have a little practice. The next board batch will be pick&place and a board with soldering mask. Not having a soldering mask mask hand soldering of course harder.


      • Low-cost plastic solder-paste stencils could be part of a solution to hand soldering, though I have not used them. Google shows this: http://www.smtstencil.co.uk/ but there will be others.

        Then you could probably melt the solder paste with a hot-air gun, or perhaps place the PCB on a hot plate and wait. Of course, a professional assembly job is best.


      • Thanks for the link. Yes, we do have a reflow oven, and for some boards we have stencil masks too. But not such a nice stencil-mate. Probably not worthwile, as typically there are only a very few boards in a series.
        And about the ‘dark side’: oh yes, that already happened several times :-). Not a bad thing at all, if software engineers are getting familiar with the world of hardware engineers πŸ™‚


    • Hi Mark,
      you must have been looking over my shoulder today? We discussed and finalized today the manufacturing of the boards. I think we will be able to submit the order tomorrow, and then it might take a few weeks until we have them in our hands.


  7. Pingback: Added Micro SD Card Socket to FRDM-K22F | MCU on Eclipse

  8. Pingback: tinyK20 Board in Manufacturing | MCU on Eclipse

  9. Pingback: Production tinyK20 Boards arrived! | MCU on Eclipse

  10. What is the part number of the smaller 8Mhz crystal on this board? slowly working on KiCAD version of the board, creating a Digikey shopping cart for it. I actually think the through-hole 1.27mm programmer headers will save a bit of space still, but potentially add more vias


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