My take on the classic Little Wire USB stick: surface mounted parts, as small and flat as possible, with an option for 3.3V operation, and optionally a micro or mini USB connector. Still solderable by hand!
Notice: I’m selling some of these on Tindie.
The idea is not new in any way - the basic schematic + VUSB library, popularised by Little Wire, has been adopted by some successful projects: DigiSpark, Adafruit Trinket, as well as some perhaps less well-known ones like picoDuino and USBasp-t.
The design of this board is directly inspired by the latter two. The differences are:
- USB connector directly on the PCB, with the micro and mini USB sockets option.
- An option for 3.3V operation (in which case the bottom side of the PCB needs to be populated and the zener diodes can be omitted).
- Standard AVR ISP header, like Little Wire. This can be used initially for programming the attiny85 (with the micronucleus bootloader) and after disabling RESET via fuses, it functions as a normal ISP header with attiny85 acting as a programmer.
- A solder jumper to select between 3.3V and 5V.
- Selecting whether to supply power to the ISP header is done also via a solder jumper.
The board in between the two little2wires below is my AVR ISP level translator, based on GTL2003 chip, with 3V3 regulator and designed to be as flat as possible.