We've recently built a highly miniaturized Arduino (pictured below) that may be interesting to some of the members of this forum. It's in the form of a 10mm x 10mm x 1.5 mm encapsulated module attached to a 25 conductor polyimide flex cable with conductor pitch of 0.3mm.
The module includes an Atmega 328P chip with a 2.8v LDO regulator, an inverter that is useful for interrupt management, a dedicated I2C interface, an SPI interface and several other digital and analog I/O options. Schematics and an Eagle layout are available at www.potomacmeso.com
. We built this setup for wireless sensing applications, but it probably would be useful in other areas where miniaturization is important. If there is enough interest, we may offer this as a product. Right now we're comp'ing a few of these to advanced users with miniature applications.
Comments and suggestions are always welcome.