I'm far enough along that I can be posting about this thing.To the left is a PCB board I designed to be the platform for the "Nex10" - the next level of the "X10 Book".
The goal is to create an X10 controller that is user configurable without the need to change the software. The Nex10 is configured through text files copied to it's SD card. More on the functionality later. This post is about the hardware!
A larger picture of the board is here.
In order to support reads and writes of the SD card, I went with a larger microcontroller - the ATmega644P. This has twice the program space of the ATmega328 used in the X10 Book. The board also has an external EEPROM, RTC (real time clock), piezo, and IR detector. It also has a difficult to solder FTDI chip that allows it to be programmed via USB. I see this as totally optional. I just wanted one to make my development easier. Besides, it's pretty cool!
Other little goodies include a resettable fuse, ISP header, and jumpers for power, auto-reset, and ARef. It runs on regulated 5V and has a voltage regulator that supplies 3.3V for the SD card. It uses a 16MHz crystal or resonator.
I used CadSoft's Eagle to create the schematic and lay out the board and BatchPCB to fabricate it. This is Rev. 1, and amazingly everything worked. If I decide to make a Rev. 2 there are a few changes I'd make, but basically I'm pretty happy. (Eagle files here.)
This board will drive an 8x32 LED Matrix from Sure Electronics. This display is very easy to read, cheap, and uses SPI so no additional hardware is needed on the board.
There is nothing about the board that is dedicated to Nex10 application - it can be used for just about any microcontroller project.
If you'd like a board very similar to this one (with a serial interface), a fellow maker, Florin, sells an easy to solder kit. You can read about it here.