Adafruit's Trinket is a tiny $8 development board that packs a punch.
People often lament that leaving an entire Arduino inside a project is not very cost effective, nor space effective. While creating an entire custom circuit is an option, another is just to find a smaller and cheaper replacement. Adafruit has just announced their tiniest and cheapest Arduino-compatable development board for exactly this purpose.
The Trinket is tiny. Its dimensions are 31mm x 15.5mm. It could literally be hidden in a hem or cuff. You could mount this in a baseball cap and never notice the weight; too bad the same can't be said for batteries. The Trinket comes in two versions. The 3v model, which runs at 8Mhz and the 5V model that can run at either 8Mhz or 16Mhz. Both versions cost $7.95.
Here are the features from the Adafruit website:
ATtiny85 on-board, 8K of flash, 512 byte of SRAM, 512 bytes of EEPROM
Internal oscillator runs at 8MHz, but can be doubled in software for 16MHz
USB bootloader with a nice LED indicator looks just like a USBtinyISP so you can program it with AVRdude (with a simple config modification) and/or the Arduino IDE (with a few simple config modifications)
Mini-USB jack for power and/or USB uploading, you can put it in a box or tape it up and use any USB cable for when you want to reprogram.
We really worked hard on the bootloader process to make it rugged and foolproof, this board won't up and die on you in the middle of a project!
~5.25K bytes available for use (2.75K taken for the bootloader)
On-board 3.3V or 5.0V power regulator with 150mA output capability and ultra-low dropout. Up to 16V input, reverse-polarity protection, thermal and current-limit protection.
Power with either USB or external output (such as a battery) -- it'll automatically switch over
On-board green power LED and red pin No. 1 LED
Reset button for entering the bootloader or restarting the program. No need to unplug/replug the board every time you want to reset or update
5 GPIO -- 2 shared with the USB interface. The 3 independent IO pins have 1 analog input and 2 PWM output as well. The 2 shared IO pins have 2 more analog inputs and one more PWM output.
Hardware I2C / SPI capability for breakout & sensor interfacing.
I got my hands on one when I ordered a bunch of LED toys and was able to get it up and running, powering a ring of LEDs in less than five minutes thanks to the Adafruit tutorial system. I did have to solder the header pins on, so maybe we'll say 10 minutes. Having it on my work bench, I couldn't help but get a picture to compare the size between this, the teensy 2.0, and the Raspberry Pi. These are not products you would usually compare, but they were available.