Vermes
Advanced Member level 4
This programmer is equipped with buffers at the output 74LVC125, so it can operate with two voltages +5V and +3,3V.
The processor is powered from 3,3V (stabilizer LM1117-3.3), so it is separated from drops and rises of voltage during connecting/disconnecting from the target systems.
Schematic:
Another important and basic assumption was that the device should be as small as it is possible. As you can see in the picture below, the PCB is almost of the SD memory card size.
You can use an old housing from a card reader as a miniature housing for the USB. As it is already a hole in the housing, you only have to put a LED in the right place. The other two diodes are red one in the bottom left corner for indication of the programming process and green LED in the upper right corner – it indicates presence of voltage at the output – because it can be turned on by a jumper derived outside.
Pictures:
Link to original thread - USBASP dwunapięciowy klonik - wersja mini