Joe Saavedra writes:

This tutorial will go through the steps involved in fabricating your own Arduino-compatible circuit using just ~$8 of parts (this includes the ATMega chip!). This is perfect for installing and embedding in permanent pieces , as you don’t need to waste a full $30 Arduino board in a project you will never need to reprogram or touch ever again. It is also great because you can solder any custom circuits (LEDs, other ICs, any external analog circuit) on the same board, and customize in terms of shape and size.

He purposfully makes all the connections on the top side of the board to make it easier to learn how to wire this circuit up yourself! The photos are great, the language is accessible, making this a tutorial you’ll go back to over and over for lots of projects!