According to Stephan, the new card stackup fits perfectly into a USB connecter, measuring 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,” Stephan wrote in a recent blog post.
“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.”
Nevertheless, says Stephan, not much has changed between the two versions in terms of function, except the number of PWM channels. Meaning, the card is still recognized as an external USB drive and can be reprogrammed using an integrated bootloader.
“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,” he added. “Two groups of 2 LEDs will therefore always have the same duty cycle.”
Interested in learning more? You can can check out the project’s official page here.