Hi,
I have locked myself out of a few ATMega8's. Searching around I have found the open source rescue shield -
Looking at the schematic it looks as if the only pin that gets the high voltage is reset, everything else is simply a case of pin mapping between a good chip installed with the related sketch and the bricked chip.
Am I missing something ? If not I will setup a 12V supply from 8 AA Batteries and hopefully unlock some chips.
Thanks
Duane B
it looks as if the only pin that gets the high voltage is reset
yes, that's correct. HV ONLY on RESET.
Plus needing a full "parallel port" worth of connection between the programmer and the target.
For many "lock out" scenarios, you may only need to provide an external clock and perhaps slow down the SPI used to drive the ISP port... See Adafruit's modifications of ArduinoISP here: Arduino Hacks -Burning bootloader chips using an Arduino
(the main modification is that they set up the "programmer" chip to provide clock to the target, instead of counting on it having some sort of working clock of its own.)
Hi,
I successfully used your (I think its yours ?) optiloader to get the bootloader onto some of these chips, but have subsequently locked myself out. Do you think a slowed down optiloader would work as a first try at resetting the fuses ?
Duane B
Seems you are not missing anything.
Hi,
With a big thank you to optiloader, I have six chips programmed, I am still locked out of another four but they can wait for now.
The problem appears to have been with my USB Port. I damaged it yesterday, I only discovered this because my phone is not charging properly and I know that at one point I shorted it yesterday. I was not able to program my UNO through the port today and so I have reinstalled the driver on another port and its all good now.
Anyway another shout out to optiloader for being such a great tool.
Duane B.
The problem appears to have been with my USB Port. I damaged it yesterday,
That's why I always have a powered hub between the computer and the Arduino. I already destroyed a hub thus I am pretty sure that this is a good idea.
Hi,
I have to agree with you, having a hub as a buffer was a top priority when I first got my Arduino, but then it just worked and kept on working and sometimes I made mistakes and it still kept working so the hub was soon forgotten about.
Until today.
Duane B
Have you rebooted and power-cycled your PC? Some USB implementations will notice over-current conditions and shut off the port (and at least perhaps, not turn it on again. Since once it's off, it's hard to tell whether anything is there.)
My Windows 7 laptop did this. I just heard the USB disconnect sound, and then nothing worked. On a whim, I went into Device Manager and found the port was shut down because it "reported a problem", so I disabled it, re-enabled it, and everything's fine.
And I use a hub now.
Hi,
All good suggestions, in my case I did reboot, the port appeared as a generic com port, the IDE was not able to communicate with the Arduino. I reinstalled the Arduino driver and its all good for now.
This is on a very old laptop running Windows 2000 server
Thanks
Duane.
On my little Win7 laptop I've encountered the "USB disconnect/reconnect" sound many times while experimenting with the Aruduino and I've never had to reboot and never damaged any ports so I guess I'm lucky 
Now that you mention it though, a hub would be a good idea. But -- would it need to be a powered hub to provide protection to the PC's USB port?
Yep, powered. Some passive hubs might have a fuse in them that would blow if the current exceeded some specific limit, but that's a last resort failsafe, and chances are you'll shut down the power transistor in the USB port first. Perhaps permanently.
You might still sacrifice the hub -- but that's presumably cheaper than whatever hardware you'd have to replace in / like your computer.
