by Sutajio Kosagi

An ARM board that fits inside your USB connector

View all updates Feb 02, 2018

Final Week of the Campaign: Plastics and Bootloaders

Hi everyone, and welcome to the final week of the Tomu campaign! The campaign will be wrapping up at the end of the week, but since we’ve already met both stretch goals, every Tomu we ship as a reward will include a plastic case, as well as an easy-to-use DFU bootloader. I’d like to take a moment to discuss these two stretch goals, and how we’ve been working on fulfilling them so far.

Tomu is on Twitter! Tweet us @tomu_im.

DFU Bootloader

The DFU bootloader V1.0 was released at LinuxConf Australia 2018, and we’ve received a lot of feedback. We’ve put together a document describing API V2.0, which we’ll load onto every Tomu that we make. V2.0 is more flexible in how programs get loaded, and adds the ability for a program to indicate sensitive areas that need to be erased before a new program is loaded.

We’re still considering features to add, so if you have feedback on the bootloader or features you’d like to see, get in touch!

Plastic Case

The case is designed in FreeCAD, and is available on GitHub. We’ve modified Tomu to make it fit into a case better:

  • Tomu is now 10 mm wide instead of 11 mm wide
  • The lanyard hole is larger

FreeCAD rendering of the Tomu case (top)

If we make the case top transparent, you can see that the EFM32 microcontroller sits inside of a cavity, and space has been carved out for the resistors and capacitors. The LEDs are covered, but that’s okay because we’ll use clear plastic for the case! A combination of the component cavities, endcap, and mounting peg all serve to prevent the PCB from moving around too much.

FreeCAD rendering of the Tomu case (bottom)

If we look at the case from the bottom, one thing becomes very apparent: there is now a mounting peg that runs through Tomu. The idea here is that in order to permanently install Tomu inside the case, the peg would be "heat-staked" down. That is a process where a hot iron is used to press down on a piece of plastic to melt it into a flat rivet. Because the case makes debugging impossible, we’ll ship Tomus and cases in the same bag, but not melt the rivet for you. This gives you the option of making the case permanent if you want a more secure fit.

Final Week

It’s the final week of the Tomu crowd campaign! Six days left to back Tomu, and receive fun, tiny USB computers to play with. Six days left to help us put a computer in every USB port!

$86,595 raised

of $100 goal

86,595% Funded! Order Below

Product Choices



A computer in your USB port! One Tomu board with two buttons, two LEDs, and a 25 MHz CPU, all fully assembled and tested.


Sutajio Kosagi

Sutajio Ko-usagi supports and produces open hardware products designed by bunnie and xobs.

Tim Ansell


Sean Cross


OSH Park

Prototype PCB Manufacturer

See Also

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