I'm sitting and staring at my project box (glumly) and thinking about Packaging (the worst part of every project!). Just about decided to use a Mega/Due protoshield. But as I stare at my Due I see that the small headers inside the board perimeter (ICSP, SPI, JTAG and DEBUG) have pins sticking up plenty far enough to contact the pins of components soldered into the shield board above.
I was going to leave those component pins long, see, so I could wire wrap on the back of the shield. Hmm.
If I use extra long female header pins can I perhaps elevate the shield high enough so that component/socket pins will miss the conductive stuff below? Or alternatively, is there any reason why I shouldn't take a pair of sharp di-cutters to my Due and chop off all those pesky unused pins?
A shield would definitely be the best way to package everything compactly, but I don't want to get all my components soldered onto the shield board and then find out there are dangerous mechanical conflicts with the Due board below. Hrrmph. Any advice from those who have already stuck shields on Dues/Megas would be welcome.
[afterhought] oh DOH! although everyone shows female long-pin headers being used to attach shields, there's no reason I couldn't use regular M/M pins which would elevate the shield somewhat... since I'm not planning to stack any further shields on it. I've been looking around for even longer m/m header pins but so far no luck, can only find the standard length.
IMO the SPI header is the only one you will have to access. If you want to access all pins when there is a shield above the DUE, this Mega/Due shield that you can find at crossroadsfencing.com may be handy:
You can buy protoshields with unsoldered headers.
Mount regular M/M strip as required.
If you want to stack, buy stackable header strip.
The Due is low profile with micro USB. The Mega has the monster USB socket which requires a bit of insulation.
Personally, I find protoshields to be a neat and tidy way to build a prototype. It is both electrically and mechanically robust. I have point to point wiring on the underneath of the protoshield. It does not interfere with the Due. I do not mount components on the underneath. Check clearance first.
Anything is better than breadboards with trailing wires.
You can mount any external sockets or connectors on the protoshield. I doubt if many projects want or need 40 screw terminals. But that option is available from crossroads.
At the moment I am considering two different Mega shield boards (they both appear to be pin-compatible with the Due); one is the black board from NKC. available from Adafruit, and the other is a cheaper (green) offering from "electronics salon" which doesn't have prefab bus bars. The fancy one from crossroads with all the screw terminals is way kewl but I think overkill for my immediate need.
To figure out the pin conflicts, I put a Due on the bed of my scanner and scanned it (horrible fuzzy image, but good enough for the purpose); also scanned the ES board and then used GIMP to overlay the two. Thus trying to determine which areas of the shield board should not have pins sticking down, for fear of contact with pins sticking up from the Due. It's a bit tricky. This is my very first shield board so I'm doing a lot of thinking before soldering
Originally I was going to solder the i2c components into the shield but then thought, that's stupid... now planning to fit the shield board with sockets, so that breakouts like my rtc, FRAM etc, can be replaced easily. Planning to wire wrap on the underside of the board (this is why I want to leave the pins long and am concerned about clearance). Scratching my head over wire routing, trying to avoid noise/crosstalk...
This is the first time I've tried to package this project neatly, rather than in a sprawling oversized messy box. It's a serious challenge! The key seems to be repeated layout drawing -- many revisions, until I get it right. Also test-fitting before soldering to make sure of those pin clearances... I live in dread of a barely-audible Zot and a whiff of smoke...
UPDATE: To my amazement and relief my soldered and wire-wrapped shield worked the first time! Everything (3 i2c components) is still talking, despite being banged around on the bench during the wire wrap ordeal. I'm chuffed. First shield I ever built.
The biggest packaging challenge appears to be getting signals into the project box from outside. I don't know where to find nice-looking connectors; I use a clunky RJ45 breakout and cat5e for some of my incoming lines, and others, well, they're just jumper ribbons... I know the robotics and RC folks have all kinds of connector standards but I've never got familiar with them.
Right now I'm kind of wishing I had used one of crossroads' killer screw-terminal shields. That makes it soooo easy, no head scratching at all.
