MightyOhm.com

Hi!

This is just exactly what I was looking for, to make setting fuses a breeze.

Recently "bricked" some Atmega168s while I was poking around with fuses, and Avrdude doesn't make it that easy.

However, I have a lot of the parts lying around already, and was thinking of just purchasing the PCB.

But I do not have components for the DC-DC convertor and wish to use a 12V supply instead as I already have one.

How should I go about "bypassing" the DC-DC convertor and using my 12V supply instead?

Thanks so much!

edwardchuajh -

Yes, it is possible to bypass the onboard DC-DC converter. See the schematic I created to illustrate this below.

The 12V supply needs to be switched on at just the right time during the programming process, so you'll need a couple NPN transistors and some 1/4 or 1/8W resistors. Almost any NPN should work, 2n2222, 2n3904, etc. You'll need to pick up a couple signals by soldering wires to various points on the PCB - hopefully this will be clear from the schematic. The new components could be placed on a small breadboard. The new circuit is outlined in the schematic. It may be helpful to compare this with the original schematic here (http://mightyohm.com/blog/products/avr- ... nd-layout/).

I haven't tested this new circuit, but I don't see any reason why it shouldn't work. You will need to make sure that your 12V supply shares a ground with the rescue shield - this is easily achieved by wiring the ground wire of the 12V supply to one of the GND pins at the bottom of the shield (pins 4 and 5 of the Power and Reset header, as shown in the schematic).

Let me know if this helps or if you have any more questions.

Thanks!

Thanks for the schematic! It seems clear, I'll be ordering the pcb in awhile and will try the modification and post my results here.

Thanks again!

Hello Jeff
Personally I'm using device like from this project
http://diy.elektroda.eu/atmega-fusebit-doctor-hvpp/
This is project made by Polish colleque. Bellow the Polish part of description You can find also English translation so I think everybody will be satisfied.
A count of AVRs possible to rescue with this device is very huge. HVPP and HVSP modes are available. Some uP You my recover just with using this circuit, others require a simple adaptors to be "pinout compatible". As I'm dealing mainly with ATmega 8/16/32 - I need no additional adaptors.

I'm posting this information just to propagate that other project exists - I'm not about showing no respect to Your solution.

Regards
Pawel