This project started as a result of my frustration and consternation with etching my own PCBs. Now, if I could draw out a board to perfection in Eagle on the first try, I probably wouldn't have thought of doing this. However, my Eagle skills are somewhat lacking, as are my soldering skills. I needed a simple way for me to avoid having to build and debug large and complex boards for each project on my list. In addition to reducing the risk of me screwing up a large board, I found that it creates a bit of a "plug and play" environment where I can add and remove modules as needed for my various projects. Changing from a robot controller with motor driver and sensors to a temperature sensor with LCD display is as simple as swapping out the modules you need and reflashing the AVR. (I know, I don't have an LCD module yet, but I will!)
As I took a look at some of the projects I wanted to create, I realized that there was a common basis for these projects; what I will call the AVR baseboard. There was always a socketed AVR (atMega168 for me), a reset button w/ resistor, and a decoupling capacitor. I wondered if I could build a VERY simple AVR baseboard and then just create modules for the functionality I wanted to add to it. Hey! While I'm at it, I could make them all stack together in a nice neat stacking bus arrangement. At first, I thought it was going to be a bit ambitious for someone of my skill level. Well, I did it, it seems to work pretty well, and I want to share it so that I can inspire others and also (selfishly) get some good feedback from the community on improvements, errors, etc. Here's how it goes.
Note: In this tutorial, there are several pictures of actual PCBs that I etched for this project. In most instances, you can plainly see the traces on the under side of the PCB when viewing the PCB from above. This is because the copper clad I bought off Ebay was super, super thin. At first I was cursing myself for being ignorant and not knowing what I am buying, but now I kind of like the stuff. I can cut it with regular scissors. It also bends very nicely, so a strip of it could be used in clothing or in a rounded panel for mounting LEDs, etc. Its not so great when you are trying to create a structured project like this one, but I managed to work through it. I worry about the flexing causing weakness in the solder joints and causing pads to lift. Nothing like that has happened yet though.