I'm building a small laptop-ish device in a briefcase. Imagine the green wires aren't there. The LCD half lies somewhat deeper in its case than the keyboard part.

For now, testing and programming, I'm using four wires (2x I2C, ground, 5V) to connect the both parts. However, that isn't that neat. When closing the case for example, you should look after the wires in order for them to stay in the case. First solution of course is shorter wires, but that wouldn't be that neat either.

So what I'm looking for is a neat way to do the inter-board communication. It should be easy to handle and robust.

The normal way to do this in a laptop is to wire it through the hinges. This isn't a possibility with this case, unfortunately.

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    \$\begingroup\$ What's up with all the downvotes?! Is this question just too awesome for you to handle? ;-) \$\endgroup\$ – DrFriedParts Jan 20 '13 at 10:06
  • \$\begingroup\$ Not sure, I upvoted to cancel one of them. Maybe due to "Laptop" being mentioned and the assumption it's a consumer type question. \$\endgroup\$ – Oli Glaser Jan 20 '13 at 11:10
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    \$\begingroup\$ The picture should make clear it's not a consumer product I'd think :-) anyway, thanks for the upvotes. \$\endgroup\$ – user17592 Jan 20 '13 at 11:42
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    \$\begingroup\$ One thought that comes to mind is to use two connectors, and a cable jumping between them, with the idea that the cable could be trivially replaceable if it becomes damaged. \$\endgroup\$ – Chris Stratton Jan 20 '13 at 15:52
  • \$\begingroup\$ I also thought about that. What kind of connector would you recommend? A common header isn't solid enough, is it? \$\endgroup\$ – user17592 Jan 20 '13 at 15:55

The obvious and silly approach is to put a battery in each half of the design and communicate wirelessly...

This is called a "clamshell enclosure" and there are two basic practices for routing wiring through the hinge. The first, you alluded to, use cabling bundled into a minimum cross-section (round bundle) and route through the actual hinging mechanics. The other is to use Flexible Flat Cable (FFC/FPC).

Numerous mass produced cable systems for this exist (due to cell phones, monitors, laptops, etc). For starters, you could check out the Hirose FP19 series.

  • \$\begingroup\$ Very nice solution! I'll wait with accepting it for others to reply as well though. It made me think of IDE connectors from computers - I have a lot of them and they can be soldered easily. Is that okay too? I also posted a follow-up question on interference on the I2C bus. \$\endgroup\$ – user17592 Jan 20 '13 at 9:57
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    \$\begingroup\$ Yup! IDE uses stranded conductor ribbon, which is just another type of flat cable. Cheers. \$\endgroup\$ – DrFriedParts Jan 20 '13 at 10:04
  • \$\begingroup\$ Searching for "FP19" on www.Hirose-connectors.com gives me nothing. Are you perhaps thinking of the Hirose FH12 series or Hirose FH19 series? \$\endgroup\$ – davidcary Sep 29 '13 at 11:47
  • \$\begingroup\$ @davidcary -- Typo. My apologies. Corrected. \$\endgroup\$ – DrFriedParts Sep 29 '13 at 15:58

Use the rainbow coloured ribbon cable in a short arc between the halves. A clear plastic sleeve will help to ruggedise it, and an IDC connector on each end lets you replace it in minutes if it wears out (make up two cables!) The design constraints you face on a project like this are different from commercial manufacturers - you can take advantage of this to make maintenance actually easier around vulnerable areas like cables and connectors.

Plus, that ribbon cable looks awesome.

I built one of these in mahogany and brass. It was Z80 based and, unfortunately, was getting obsolete faster than I could finish it!

  • \$\begingroup\$ +1 for building a laptop from mahogany and brass, I bet it looked rather cool indeed. Now imagine if you could get a mahogany/brass Sony Vaio - I'd buy one of those without a second thought (regardless of specs, which are usually the only concern for me) \$\endgroup\$ – Oli Glaser Jan 20 '13 at 16:25

If a cable or case change is absolutely not an option, then communicating wirelessly is the only option.

To avoid a battery in both halves, I'd think about putting everything in the LCD side, then use a small IR comm link between the keyboard and other half. The power for the keyboard should be minimal, so could be provided via resonant inductive coupling (though the placement and angle of operation depending on the angle of the open case would need careful consideration, but efficiency is probably not so important as long as you keep the keyboard side power consumption down)
It shouldn't be too hard to rig up something to give it a quick test, so you can quickly verify whether it's a viable option.

Or a small solar cell and little rechargeable battery in the keyboard side could be used - solar cell on the outside of the case obviously :-)

  • \$\begingroup\$ +1 for a climate neutral solution :-) I probably won't go with wireless though, I'm hesitating on two energy sources and DrFriedParts gives a nice solution with one cable. But thanks anyway, I'd go with your solution when I really didn't want wires! \$\endgroup\$ – user17592 Jan 20 '13 at 11:48
  • \$\begingroup\$ No probs, thanks for the upvote - if a cable is an option then a small bundle or IDE/FPC/FFC is definitely the way to go (I went from the last line of your question, but I see now you are just referring to specifically through the hinges rather than any cable at all) \$\endgroup\$ – Oli Glaser Jan 20 '13 at 11:59

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