USBasp
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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.
Such keys however invert the signals, so I had to modify the firmware. Final result (schematic diagram and modified sources) are available on my website
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.I hope that someone may found it useful.