Smallest Arduino with at least 20 pinouts

I'm building a surround sound speaker system with an Arduino, but want to know if there's a really small Arduino version i don't know about with at least 20 pinouts?

Arduino Nano e.g.

How small?

The m328 in a 32CC1 or 28M1 package is 4mm by 4mm. You will be hard pressed to find a 20 pin anything in a smaller package.

There was http://staging.femtoduino.com/
It doesn't look like it is available as a product, but the design files are supposedly published.
If you don't need it quite that small, there are a lot of "Arduino Nano" (with USB) and "Arduino Pro Micro" (with FTDI Serial connector) boards available that are still quite compact compared to the original Arduino.

I offer a small card, 1.3" x 1.3", no regulator or USB connector.

But a $3 promini will do the same at ~1.2" x ~.7"

and a Nano is not much larger

and both are less than I pay just for parts.
I just bought 5 of the promini's, they say Deek Robot on the back and look to be well manufactured for a simple 328 and resonator, button, and a couple Rs & Cs. They don't have the extra power & gnd signals of mine, so will not be quite as convenient to use.

CrossRoads:
They don't have the extra power & gnd signals of mine, so will not be quite as convenient to use.

Also you have mounting holes. If you're not going to socket the Arduino into another board via headers, mounting holes are such a plus imo.

Geoff

CrossRoads:
I offer a small card, 1.3" x 1.3", no regulator or USB connector.

No crystal?

Paul__B:
No crystal?

The crystal is on the underside of those boards. The boards in that picture were built by me using CrossRoads PCBs. I wish I would have positioned one board upside down.

I currently have three boards that I have used for projects. The extra grounds really help when powering lots of LEDs!

Mark

I just bought 5 of the promini's, they say Deek Robot on the back and look to be well manufactured for a simple 328 and resonator, button, and a couple Rs & Cs. They don't have the extra power & gnd signals of mine, so will not be quite as convenient to use.

I've used many of those cheap units; never a dud. They also work well (yes, I know the caveats) at 3.3V. Mount to the back of a 2.2" 320x240 GLCD with double-stick tape.

Ray