Thursday, November 5, 2020

feegle XS


A tinier Feegle. This is the same design as the Feegle but using 4.5x4.5mm tactile switches instead of 6x6mm. The only functional difference is the lack of a RESET button. There is only a USBASP button. Holding the USBASP button while plugging in the USB cable will enter bootloader mode.

Originally planned to use the same through hole PTC fuse I use on most V-USB boards, but with it overlapping the resistors. This turned out to be too thick and would require 6mm spacers. To keep to the 4mm spacer thickness I used a surface mount PTC fuse.

Uses the same blue LEDs for the V-USB circuit and miniature 16MHz crystal.

The switches are tiny. 6mm height for the keys and 5mm for the USBASP button. I used the top plate to hold the switches in place while soldering. It would be impossible to keep them all aligned without the plate holding them in place. Since the base of the switches are shorter than most of the other components I soldered them on first, so the plate could rest against the switches firmly.

Wookie for scale. 63x46.5mm. The holes in the top plate are 2.5mm for the switches. 3mm holes for the LEDs. Flat laptop style M2 screws.

With 4mm M2 spacers the total thickness is about 9mm. I found some aluminum M3 spacers on Digikey that look much better than the transparent nylon ones and fit right over the M2 brass spacer.

I sanded one the top plates to expose the copper layer.

6mm switch on the left, 4.5mm on the right. 4.5mm through hole switches are not very common. Surface mount versions are easy to find. I found these at They are available in a few different heights and in two different actuation weights (160g/250g).

The 4.5mm switch is only 3mm tall at the base. The mini USB connector and ATmega328 are both about 4mm tall so the board can't be made any thinner.