[Blog]

My first prototype 134.2KHz RFID reader used a MAX232 level converter to connect to a host computer by RS232, but my laptop doesn't even have old-style serial ports so thanks to a micro-USB USB-to-UART bridge supplied by Dontronics (thanks Don!) I put together a reader with a USB interface.

I hadn't used the micro-USB modules before but I'm totally impressed. The module is incredibly small: it's basically just a B-type USB socket with a microcontroller mounted directly on the bottom and some header pins. They're totally plug-and-play: the device enumerates itself as a standard serial port on the host computer so you can talk to it with bog-standard tools like GTKTerm just like any other serial port, and at the other end it presents TTL-level serial I/O lines. It even provides pass-through ground and +5V connections from the host computer so you can power a device straight from it if you don't need much power.

So in the end all I had to do was rip the MAX232 off the reader, pop the micro-USB device in its place, remove the 5V voltage regulator and use the regulated output from the micro-USB instead, and plug it in. Linux recognised the device, GTKTerm connected straight through to the microcontroller in the reader, and it Just Worked.

Rock!