[Bill Porter] has a tip for designing circuits that have multiple connections ... but also called for an FTDI chip in order to reprogram via USB and a bootloader. Unlike the schematic above ...

[David] is here to help with his isolated versatile FTDI circuit. Our computers are ... Today it’s almost always USB, specifically serial over USB. USB has some safety features built-in ...

Add or Remove Programs entry for FTDI USB Serial Converter Drivers. This is a driver pack that allows USB ports to be used to connect to Serial bus devices with a USB - Serial adapter cable.