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image userial board v1.0


userial is a project building a free USB to I²C/SPI/GPIO bridge, using the Atmel AT90USB647 chip. Hardware and Software are released under an Open Source licence. It supports the following interfaces:

The board communicates with the host computer using a CDC (USB communications device class). This makes it easy to use userial without installing a device driver or special libraries. Due to the ASCII based command interface it is easy to control devices manually with just a terminal emulation. This makes it easy to obtain quick results, to configure devices on-the-fly or to control prototyping boards in a straight-forward way.

Schematics and firmware are available to the public. The firmware is released under the terms of the MIT license and the hardware is released under the terms of the Creative Commons Attribution-Share Alike 3.0 Unported License.



If you don't want to build your own hardware, then you might find the micropendous worth a look. The userial firmware should run on an micropendous board with minimal changes.


Firmware v1.1023 July 2013

userial firmware v1.10 released. The changes in this version are:
  • Fixed a bug in setting up the ADC. Thanks to Petr Kolesnikov.
  • Fixed some compiler warnings with the current GCC.

Firmware v1.925 March 2010

userial firmware v1.9 released. The changes in this version are:
  • Updated LUFA to version 100219.
  • Added support for bumble-b board.
  • The actual SPI clock divider was never written to the clock divider. Thanks to Erik Schönewerk.
  • Fixed a bug in the GPIO driver: the GPIO read command returned the value of PORTx but not PINx. Thanks to Dave Fletcher.

Firmware v1.831 October 2009

userial firmware v1.8 released. The changes in this version are:
  • Fixed a bug in the calculation of the SPI frequency divider. Thanks to Zoran Stojkovic.

All news can be read in the userial news archive.

To Do

userial is considered stable (some might call it finished). Bugs in firmware are fixed, but no new features or versions are planned.