V-USB is a software-only implementation of a low-speed USB device for Atmel’s AVR® microcontrollers, making it possible to build USB hardware with almost any AVR® microcontroller, not requiring any additional chip.

V-USB can be licensed freely under the GNU General Public License or alternatively under a commercial license.

A comprehensive set of example projects demonstrates the wide range of possible applications.


  • Fully USB 1.1 compliant low-speed device, except handling of communication errors and electrical specifications.
  • Example projects demonstrate device and host driver implementations on Linux, Mac OS X and Windows.
  • Supports multiple endpoints: one control endpoint, two interrupt/bulk-in endpoints and up to 7 interrupt/bulk-out endpoints. (Note that the USB specification forbids bulk endpoints for low speed devices, but V-USB supports them to some degree.)
  • Transfer sizes up to 254 bytes by default, more as configuration option.
  • Comes with freely usable USB identifiers (Vendor-ID and Product-ID pairs).
  • Runs on any AVR microcontroller with at least 2 kB of Flash memory, 128 bytes RAM and a clock rate of at least 12 MHz.
  • No UART, timer, input capture unit or other special hardware is required (except one edge triggered interrupt).
  • Can be clocked with 12 MHz, 15 MHz, 16 MHz or 20 MHz crystal or from a 12.8 MHz or 16.5 MHz internal RC oscillator.
  • High level functionality is written in C and is well commented.
  • Only about 1150 to 1400 bytes code size.
  • You can choose the License: Open Source or commercial. Click here for details.

For a comparison to other USB solutions for microcontrollers please click here.


This diagram shows a typical circuit for a bus powered device (click the image to enlarge).

D1 and D2 are a low cost replacement for a low drop 3.3 V regulator chip, such as the LE33. Operating the AVR at higher voltages exceeds the common mode range of many USB chips. If you need to run the AVR at 5 V, add 3.6 V zener diodes at D+ and D- to limit the voltage.

For a prototyping board, please see metaboard.

Documentation Resources

  • Download the V-USB package containing a short description and several simple code examples.
  • V-USB's git repository is on github.com.
  • V-USB Wiki is a public Wiki with lots of additional information.
  • There is also an excellent step by step tutorial by Code and Life.
  • Another third party tutorial can be found at workinprogress.ca.