Method To Reset Bricked AVR

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The Floating Brain

Joined Mar 7, 2018
16
Hello, I have been trying to figure out the best way to reset the (clock) fuse(s) on my Atmega8 which I bricked when trying to set up an external clock (no idea what I was doing in terms of the settings to be honest). I set it to be a low frequency external crystal oscillator with the highest delay setting possibly, but I don't remember which one.

I have heard of primarily 2 methods to reprogram the avr


Option 0:
The first is to have another AVR output a 1 MHz clock signal (I am using this guide as I cant find the settings shown here [I dont see a CKOUT fuse as an option]). The problem being here I have no idea how to set this up in terms of the hardware: what pins do I need to connect, what goes to them, etc. after I do connect them, what resets the fuse? Also I have a tiny breadboard and don't want to rip up my whole project, but was thinking about buying a new breadboard anyway.

Option 1:
The second option I know of is HVPP. I do have an Arduino UNO I could use to do this as I have seen, but Im not sure I have all the parts, however I did see the schematic of one person here. To be honest, I have no idea what is happening to the right of this schematic, however on the left I am thinking I may be able to rig up my Pololu USB AVR Programmer v2.1 to make a circuit like this, in fact it seems like he has one in the background of his video on this topic. (Side note/side question: The 12V connected to the NRES pin makes me nervous, can someone explain why this wouldn't fry it? It is connected in series and before the transistor. Does it have to do with how he is getting power from the Arduino board?) Also, in Atmel Studio, it recognizes the Pololu as an STK500 (though it looks no where near as fancy) and has an option for HVPP


(clarification on the image, this is a different Atmega8)
debug2.PNG


Of course there doesn't seem to be enough power to do HPVV

debug1.PNG


I don't know if this mode is a weird remnant of it thinking its an STK500 (which notably also has a JTAG mode where as this does not, so maybe it is distinguishing between the two and is just based on the original STK500 software), but if not, maybe it is possible to rig the Pololu to reset the fuses on my Atmega8?

Option 2:

I found this I don't know what most of these settings do, I modified them to work with an Atmega8 and STK500 but nothing else. I tried and got nothing, is this a viable approach?


I am looking for the cheapest, easiest, fastest approach to reset the clock fuse (doesent have to be all the fuses), preferably without buying parts specifically to do this.


Thank you, for reading
- TFB
 
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