Every I²CMini has a unique name

SPIDriver, I²CDriver and I²CMini all use FTDI USB interface chips. Specifically, they all use the FT230X. These parts come with an 8-character serial string, assigned by FTDI and guaranteed unique. You can change it - there's a utility to do that, but I prefer to leave it as-is and use the string as the device ID.

As part of the SPIDriver and I²CDriver program-and-test step, the QA program prints a label with the serial string on it. If you have one, it's on the bottom of your unit:


(The tiny Dymo 450 thermal printer that I bought do do the original Gameduino 1 labels in 2012 is still going strong. Super-reliable and Dymo properly document the complete protocol. Good stuff.)

This string is shown by the GUI when you connect to your I²CDriver:


And it's accessible from Python as well:

>>> from i2cdriver import I2CDriver
>>> print(I2CDriver("/dev/ttyUSB2"))
<i2cdriver1 serial=DO01ILFP uptime=322911, SCL=1, SDA=1>
>>>

So it's quite useful having a serial number on the thing itself, especially if you have more than one. Doing this for I²CMini caused a rethink -- at 18x18mm it's too small for a sticker, and in any case the bottom has silkscreen on it already. What was needed was a way of printing the serial number on every unit, hopefully quite quickly and cheaply.

I first wondered about small print heads, and couldn't find anything. But then it struck me that my trusty K40 laser cutter (this model, from ebay) could probably write text on the solder resist. A quick test confirmed that yes, it can, and the effect with the black ENIG boards was quite readable.

So here's the result. After making a little fixture to hold the PCB steady, and hacking up a script to turn the Hershey vector font into SVG, a few seconds in the cutter and a rather nice gold number is printed on the back. Here's DO029IBC, printed this morning:
This is just a test, for production I'm making a tray that holds 100, so they can be printed in a batch.

Thanks for reading.