ATtiny12 fuse

  
Plug an ATtiny12 into the 8 pin socket and hold down `GO!` button. The LED will come on at the end of the programming process, which only takes a couple hundred millisecond. The fuses are now restored to their factory default states. This picture was taken before the voltage doubler, made with the 1N916 and 100 uf capacitor were added. The second 2N4401 -the one with the emitter grounded is only there to make sure that pin 1 of the ATtiny12 is pulled to ground when its supposed to be grounded. Note that D9 is set up with a weak pull-up of about 100 uA so that a base resistor is not needed in series with the 2N4401 base. I didn't use a 2N2907 as the PNP in the circuit I built because I have a bunch of similar transistors with a strange part number (if you have a data sheet for a 2NSA1020Y please contact me) so this aspect has not truly been tested, though the circuit was designed for a 2N2907.
ATtiny12 fuse - schematic

For the details of the programming algorithm, see the Atmel ATtiny12 data sheet. All of the necessary signals are generated by the AT90S1200A . which is clocked by its internal oscillator. If you wan to use an AT90S1200 (non-A) you will have to add a crystal or ceramic resonator and load capacitors. The +12v programming voltage is developed in the switched analog regulator made up of the 2N2907 and the 2N4401 that serves as the error amplifier. +17 Volts to supply the switched analog regulator is generated from a 9 volt power supply, in my case, a 8.4 volt Ni-MH transistor radio battery. The 100 uF capacitor charges to the battery voltage through the 1N916 and the internal circuitry inside the 7805. If you have any doubt the capacitor will charge fully, you can place a 1K resistor from the regulator's input to ground. When the "Go" button is pressed the charged 100 uf capacitor is placed in series with the 9v battery supply and the battery is applied to the 7805, thus providing +5V to the logic and +17 volts to the switched 12V supply simultaneously. Since the +12v is only on for a few milliseconds, the voltage on the capacitor does not droop enough during the programming period for the switched 12 volt regulator to go out of regulation. The AT90S1200 and ATtiny12 sockets must be empy for this procedure. If there are parts in these scokets, remove them before startring this procedure. 2. Temporarily but securely jumper...



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