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USBasp - MV


USBasp designed by Thomas Fischl is a very nice and cheap AVR ISP programmer. However the original version theoretically does not allow to program AVRs powered from voltages lower than 5V.
Because I wanted to use it to program new AVRs working at c.a. 2V, I had to modify the original circuit.
To keep design as simple as possible and to avoid using integrated level converters (which are sometimes difficult to buy), I have decided to use simple transistor keys with Schottky diodes to convert logic levels.
The schematic diagram of modified USBasp is available as the kicad project (sorry, I haven't designed the PCB - my device was finally mounted on an universal PCB). You can also download it as the PDF file produced from PostScript generated by kicad.
The transistor keys change polarity of signals, and therefore some changes in the firmware were necessary. Additionally I have used different AVR (ATmega88) and changed use of some pins. My firmware was based on the original usbasp.2009-02-28.tar.gz written by Thomas Fischl. You can download my modified sources, or just my patch (which may be usefull if you would like to patch another version of firmware).
Please note, that due to delay introduced by the transistor keys, you may need to add the "-B" (e.g. "-B 3") option wen invoking avrdude with this version of USBasp.
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Last modified: Mon Apr 26 21:51:15 CEST 2010