SparkFun Forums

[gruvin]

Let's say I had an existing product that used an AVR ATmega64A. Let's say that chip was in a TQFP package (splayed out leads) and soldered to the product's PCB. Now I want to hack about with said product. (Specific example can be found at Google Code project gruvin9x -- http://code.google.com/p/gruvin9x/)

What if there were unused pins I wanted to make use of -- and pins I wanted to change the function of, involving some external re-wiring.

The attached image shows what I've had to do without any Spark Fun magic. Now ...

What would be cool would be if I could de-solder the stock chip, throw it away and replace it with a socket. Then I'd love to have a Spark Fun break-out PCB with at ATmega64/128/whatever AND a plug on the under-side that slots into the new socket on the original PCB. Following me so far?

Now I can readily access all the pins on the MCU, routing the original wiring to the original locations and re-wiring those I want to do new stuff with. There could be a convenient ICP connector on the board already of course -- just like your existing break-out board product.

Can it be done? I found at http://www.winslowadaptics.com/ that they have a solder-down board that can replace the original TQFP component and break-out to 64 pins in a compact multi-dimensioned array. See here http://www.winslowadaptics.com/product/14679. Good start!

That product itself plus a nifty SparkFun PCB to plug on top of it could well do the trick. But I'm sure you geniuses could work out something much better using just the solder-down part off the bottom and do the rest yourselves, no? (If it's available separately.) And I'm pretty sure there are "plugs" to go in sockets as I described above. That same company does have PLCC plugs like that. But I don't think there are any PLCC sockets that will readily solder to existing TQFP pads.

Cheers!

[gruvin]

If there's just no such thing as a 64-pin QFP plug to fit a QFP socket, then what about adapting 0.8mm pitch SIP pin strips (they exist, right?) to solder to the original PCB? These could be bent at 90 degrees and soldered to a suitably sized carrier board where they then just stick straight up. Now we have a "plug" on the original PCB.

Then all we'd need is an adaptation of your existing AVRmega128/103 break-out board with 0.8mm pitch SMD DIL sockets on its under-side and we're away!

Or, I guess you could put the SMD sockets on the lower PCB and have pins out the bottom of the break-out.

Go on! You know you love it. Let's get hacking!