Thoughts on this circuit (My first one)

As I said, it is likely more economical to buy a module off ebay or sparkfun (the entire module is likely cheaper than you getting a single board), however if you want to do it as a learning experience there isn't any reason not to do it other than cost (and learning always costs anyway!). Off the top of my head (meaning there are probably things I know you should do but have currently forgotten ): the reset circuit of only a resistor won't work in the real world. At power on the reset will go instantly high and not actually reset the chip. In a standalone circuit there is usually a largish capacitor (1 to 10 uf) from the reset pin to ground. That at power on holds reset low til the resistor charges it up resetting the CPU and then starting it.You should have bypass capacitors (typically a .1 uf ceramic in parallel with a 1 to 10 uf tantalum) as close as possible to the power and ground connections to the CPU (as when ports are switching there are high current draws on the power pins which can pull down the supply voltage and cause problems). You likely want a set of .1 inch connectors for each of the CPU I/O pins so you can connect things to it. You likely want to provide a method to program it (either via a serial port and the Arduino bootloader or via the isp pins) unless you are going to load the program externally with a programmer and plug the CPU in with a fixed program. Looking at the Arduino Uno schematic (available on the Arduino site ) should give you some hints about how they do it (although thats a lot more complex than what you are currently doing). If there are any pro mini schematics (check the sparkfun.com web site) that is probably closer to what you are trying to do.