In many microcontroller projects you might want to add an USB interface which is based on USB to serial converter. There are many chips available that does this job well. Most popular is FT232R or similar which is quite expensive and in some projects it can be too pricy. If you look around, you will find that there are tons of alternatives that cost cents. Ian suggests to take a look at CH340G chip which costs as little as 40 cents. Of course it comes from China market.
He purchases several of these and built eagle part so everyone could easily include in project. Since datasheet of this chip is scarce, he’s done the hard work by finding pin-outs and drawing typical schematics for 5V and 3.3V circuits.