Here is some INFORMAL documentation on the main Arduino Mini by a fan. It might be totally wrong, until this page says otherwise.
Note (02/05/2014): FIRST Thing: Determine which version of the Mini you have: 3, 4 or 5. Some newer versions had the ATmega168 or (now) the ATmega328, so check closely which MCU you do have. If you arrived here somehow other than from Arduino Web Site, please refer back to Arduino Mini Site to get the latest information and schematics and: See the guide to the Arduino Mini and the Arduino Mini hardware page.
Warning: Don't power the Arduino mini with more than 9 volts, or plug the power in backwards: you'll probably kill it.
Chip Refs:
Here's a picture of the mini in a bare-bones circuit, with just power, reset, and an LED on pin 13. Click to see larger image, which I have annotated on flickr:
As with the other ATmega chips, the basic idea is this:
Reset is done by taking the reset pin low briefly, then taken back to high. It should then be held high, normally. If it is left to float unconnected, it may cause unplanned resets. Immediately after you take the reset pin high again after it has been low (i.e. immediately after you release the reset button) pin 13 will blink rapidly for a second. (for me, 3 pulses in about 1 second)
Wiring a reset switch:
See also this forum thread on adding a reset button.
The main page already details this, pointing at this diagram.
Here's an annotated photo (on flickr) of a mini along with a usb connector:
March 26, 2009: The circuit in the photo seems to be wrong. 10K resistor not connected between RESET and +5V
Note however, that:
You don't need a Mini USB Adaptor to program the Arduino Mini. You can also program the mini through an Arduino NG board, as follows:
Binary sketch size: 4816 bytes (of a 14336 byte maximum).
Atmel AVR ATmega168 is found. Uploading: flash Firmware Version: 1.15 Firmware Version: 1.15
There's already a page on troubleshooting. But here's some mini-specific stuff.
My program uploads ok, but the mini does crazy stuff (e.g. pin 13 led blinking in a fast dim blur).
You may have uploaded with Arduino IDE set to work with an atmega8. Make sure that Tools:Microcontroller is set to atmega168. I think it'd be better if such comms were simply rejected between the IDE and the Mini, or at least if Arduino IDE gave a warning after such a mismatched upload.
Like many playground pages, this is user-contributed info, not formal documentation. Use it at your own risk. The mistakes are neillzero's - the correct bits, Gianluca's and Mellis'.