bypassing DC-DC converter?

[edwardchuajh]

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!

[mightyohm]

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!

[edwardchuajh]

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!

[Loslobos]

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