Miniature USB to serial PCB

Description

A small FT232 USB to serial adapter built to fit directly in the USB port

Features

Integrated USB header
Standard FTDI cable pinout
Single sided PCB (easy to manufacture)
Rx,Tx led’s
Miniature size

Development

Lately I have been developing several projects that use a FTDI chip to provide USB interface to a computer. Instead of using a Sony Ericson dss-20 sync station all the time, I figured it was time to develop a dedicated solution that fits directly in the USB port. I have a bunch of FT232BL chips that I bought extremely cheap in Huaqiangbei last time I was there, so I based the layout around that chip. On the serial side I used the same pin-out as the de-facto standard FTDI cable (GND, CTS, VCC, TXD, RXD, RTS). It was a little challenging to manually route the traces (using this method), but I think it came out quite well. You can see the whole process here in 10 times the speed:

watch in full resolution

I could have avoided the single bridge wire by routing the 3,3v (pin6) signal under the 0603 1k5 resistor, but it would have increased the risk of short-circuit. After a bit of tuning I managed to fit everything within 35×18.5mm, which is smaller than most USB memories. I manufactured the PCB by milling it using the HTML CAM to generate the g-code, but toner transfer or UV mask should work just as great. I hope that this design can come to use for others as well!

Assembly

This is not a project for the very beginner since all components are SMD (surface mount) and the LQFT 32 package has a 0.8mm pitch. However if you have access to decent equipment they shouldn’t cause any problem (solder station with a narrow tip, tweezers and a microscope). Start with the 0603 components, then the chip and switch and solder the crystal, wire bridge and pin headers last.