My Business Card v2
At the end of this month, I'll be leaving my current job. I therefore thought it'd be a nice occasion to build a new business card for my future interviews:
You may remember the first version of my business card made more than one and a half years ago (time flies!). It was basically made of two PCBs soldered together :
So why not simply assemble more of them? Well I wasn't completely happy with the way the two PCBs were assembled and wanted to try a new technique I had used for the top PCBs of the Mooltipass project:
As you can see the PCB was slightly milled so reverse mounted LEDs may be directly soldered on the board. Well for this new business card the only difference is that the LEDs are soldered on the bottom PCB:
The new card stackup perfectly fits into a USB connector as it is 2.4mm high (1.6+0.8). The old version was actually thinner so I had to apply solder on the USB pads, which was not so pretty in retrospect. You'll be surprised to know that the new card can still fit in a normal wallet as it is completely flat.
However, the hard part was to solder the two PCBs together as a 1.5mm wide exposed copper 'band' was put near the cards' edges to this goal. Using a reflow oven with the card facing up turned the soldermask yellowish so I ended up soldering them by hand with a hot air gun.
Schematics and functionalities
Pratically nothing changed between the new and the old version except the number of PWM channels. I therefore decided to switch to the ATMega32U4 from Atmel (quite costly I know) as I could re-use all the code I had made for the v1. The card is still recognized as an external USB drive (2MB!) and can be reprogrammed via the integrated bootloader (launched by sliding some aluminium foil on the 3 exposed pads on the PCB shown above). You may also have noticed that the flash isn't exposed to the outside as I wanted to keep some kind of central symmetry.
I migrated the old schematics and layout to Kicad :
For a detailed schematics explanation and performance analysis, please head out to my card v1 blog post. The only thing worth mentionning here is that given the ATMega32U4 only had 7 PWM channels I had to use a given PWM channel complementary output and two extra I/O pins to enable/disable these given LEDs. Two groups of 2 LEDs will therefore always have the same duty cycle.
End result and resources