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This project allows to reset fuses of ATtiny AVR to factory default values even in case ISP programming has been disabled or RESET has been configured as I/O pin.
On ATtiny microcontrollers, you can set the fuses to use the reset pin as a
normal I/O pin, this gives you another I/O pin. But this also disables its
ability to reset the chip, as this is required to program the chip using ISP
This circuit uses the High Voltage Serial Programming method (HVSP) to reset the fuses to factory default.
This circuit is reduced to the bare minimum. The NPN Transistor is used to apply the +12V Programming Voltage to the target AVR. The components are not critical, it is possible to use a different NPN transistor or any AVR with at least 8 free I/O pins. The AVR clock is also not critical, it works with the internal 1Mhz clock or with any higher clock rate.
HVSP Fuse Restore circuit for ATtiny13, ATtiny25/45/85 (above) and for ATtiny24/44/84 (below)
First load the software into into the ATmega8 using your preferred ISP programmer. Then verify that +12V voltage supply is applied as well +5V supply. Then press button to start the fuse restore process. When the led turns on constantly the fuses of the ATtiny have been successfully restored to factory default values. A flashing LED indicates the fuse restore was not successful.
The AVR-GCC software runs unchanged on any ATmega8 or ATmega88/168/328, just adjust MCU type and clock frequency in the Makefile. The software can be easily adjusted to run on any AVR with at least 8 free I/O pins by changing the PORT and PIN definitions in the source file.
The AVR-GCC software with source code is available here: HvspFuseRestore.zip
© Copyright 2014 Peter Fleury http://tinyurl.com/peterfleury