Tomu Hardware

I'm Tomu a tiny ARM microprocessor which fits in your USB port. I have two buttons and two LEDs.

Contact

We're available on mailing lists and IRC:

• IRC Channel - irc://irc.freenode.net/#tomu - IRC channel for discussing anything related to the project.
• Announcement mailing list - Low traffic list for announcements.
• Discussion mailing list - List for discussing development / new features / etc.

About the PCB

Built out of a 3D printed part + 2 layer "thin" PCB. LCA2018 and Crowd Supply boards are 0.6mm.

Designs and documentation are available in:

• pcb/: KiCad design files
• docs/: PDF schematics, pin-out diagrams, and 3D renders

The board requirements are very lo-fi:

• 6mil traces
• 6mil clearance
• 0.3mm drill / 0.6mm vias

The primary MCU is a Silicon Labs EFM32HG309 (datasheet, reference manual).

The important features are:

• Available on Digikey
• QFN24 - 5mm x 5mm package
• Inbuilt 5V to 3V3 regulator.
• Crystal-less USB

These make something which is almost hand solder-able fit into the tiny size.

BOM

All parts are available from Digikey, and are readily available from other suppliers.

• Kitspace Page has links to buy from multiple retailers and download the Gerbers
• Digikey BOM in CSV format
• Digikey Shared Cart

Individual Parts

• Resistors
  • 2 x 0402 - 15 Ohm - Digikey
  • 2 x 0402 - ~50 Ohm (Depends on LED choice)
• Capacitors - Digikey Capacitors 0402, >1uF
  • 2 x Capacitor 1uF 0402
  • 1 x Capacitor 4.7uF 0402
• 2 x LED 0402
  • You choice of two different colors (might require adjustment of R1/R2).
  • 5mA LEDs are better choice.
  • Get highest millicandela rating you can.
  • Digikey Search of LEDs in 0402 package
• 1 x EFM32HG309 or EMF32HG308

Case

The PCB is thinner than a USB socket, and has exposed contacts on the reverse side, so it needs a case in order to make proper contact with the USB pins, and to not short on the shield of the USB port.

Early prototypes used a business card that had been folded over, however the crowd funding campaign made enough to cut steel and make a case.

Designs are available in the case/ directory. Cases for earlier board versions tend to require higher tolerance on 3D printers.

FAQ

Why did you create this?

The aim was to prove that a device which fits in your USB port could be created by hobbyists in small quantities extremely cheaply.

Where does the name Tomu come from?

TOMU comes from the abbreviation "Tim's Open Micro USB".

What can I use this for?

What ever you want! If you do create something, please send me the info!

License

The contents of this repository excluding third_party directory is released under your choice of the following two licences:

• the "Creative Commons Attribution-ShareAlike 4.0 International License" (CC BY-SA 4.0) full text of this license is included in the LICENSE.CC-BY-SA-4.0 file and a copy can also be found at http://creativecommons.org/licenses/by-sa/4.0/
• the "TAPR Open Hardware License" full text of this license is included in the LICENSE.TAPR file and a copy can also be found at http://www.tapr.org/OHL