This one definitely falls into the "yea

[G+_Chris O'Riley]

This one definitely falls into the "yea.... but why?" category. A microcontroller on the back of a ClickMate connector!

 

I picked up some ATmega32u4 ICs for a project I'm working on. But as my only experience so far is with Tiny85's, I thought it'd be good to breadboard out a circuit before designing a PCB and having one made up. This was much easier with the Tiny85 and it's 8 pins, but I managed to get it working. Once I verified my circuit worked and was able to flash a bootloader and program the chip, I didn't know what to do with it. Some of the pins were bent and one broke off pretty close to the package, but I didn't just want to throw it away.

 

So I thought I'd see how small I could make a fully functional microcontroller out of it. I started by soldering two caps to the back of the crystal, and then glued the crystal to the chip and wired it to the appropriate pins. I linked all the grounds together, then vcc's, then added RX/TX leds and pullups for reset, etc. Then I wired all the IO pins to two female pin headers, one for analog pins/5v/ground, and one for all the digital pins. The ClickMate connector connects to the USB and serial programming pins, and I made up a cable for each to plug it into.

 

I'll probably encase the whole thing in some epoxy to hold everything in place. If wires get pulled off the pins it would be pretty tough to fix at this point.

 

I'm not entirely sure it was worth the effort to save a $4 IC. Actually, I'm entirely sure it WASN'T worth the effort just to save the chip... but it was more of a "just to see if I could" kinda thing.

 

Here's some pics for your amusement!

 

[G+_Jeff Gros]

Wow, that is pretty neat! Good job! Looks like you've got bypass caps, pullups and everything! I am definitely amused!

 

But I do agree it fits in the "Yea... but why?" category. I understand that not everyone can design a PCB in order to make a QFP breakout and then PCB express it. But for a few bucks you buy a breakout board.

 

I know, I know. You were just having a bit of fun! :)

 

And its good practice if you ever quit your day job and become a tech!

[G+_Black Merc]

That's called skills...

[G+_Chris O'Riley]

Thanks guys.

 

Buying a breakout board would have definitely been quicker and easier... but what's the fun in that! ;)

 

It was mostly just an exercise in fine soldering and just for the heck of it. This morning, I noticed I forgot the 22ohm resistors on the USB data lines so I added them in. Now I'll encase it in epoxy.

 

I think I could do a much cleaner job next time... not that I plan on there being a next time! Any finer and I'll need a microscope. The one I have flips the view... It makes soldering really difficult when you have to reverse everything your eyes are seeing.

[G+_Paul Hutchinson]

Brilliant! The blank area on the back of the QFP is a perfect size for the other components.

[G+_Chris O'Riley]

Thanks, I initially thought of gluing a micro USB connector on back, but then I had to figure out how to get all the I/O pins broken out. I could have probably snuck 5 and 3.3 volt regulators on back between all the wires, but that would have been going just too far! ;)

 

I did this with a Tiny85 and it worked out great. The legs of the '85 lined up perfectly with the ClickMate pins. I was testing something and this let me pop off the chip, plug it into another cable for programming, and then back into my little wiring harness with a few sensors.

 

Here's a pick of the Tiny with a 5 volt regulator on top.

 

 

[G+_Chris O'Riley]

Here's a photo of the 32u4 incased in some clear resin, which won't yellow as much as epoxy would.