Cable options for lots of connections to PCB? - Page 1
Forum section: electronics / projects

author: stereodanny
author_rank: Newbie
timestamp: November 29, 2021, 03:32:02 am
content: I am working on a project that involves connecting hundreds of outputs via very small gauge wire to the PCB (26 AWG or thereabouts) and I need to be able to disconnect the board from these connections periodically. The connection must also be as small a profile as possible because there is not much room in the case for a bulky connector (I can maybe spare a half-inch of height between the PCB and the case lid).The best I've been able to come up with is the biggest IDC ribbon cable I can find (even that has only 64 pins) which can plug into standard 2.54mm pitch header pins on the PCB. However, the connection is incredibly stiff (to get the plug on and off is a real hassle) and I have to separate and splice each individual wire in the ribbon to each device, which takes hours. And if I have to go over 64 connections, that's two cable headers on the PCB and it starts to get difficult to fit in the profile of my project. I'm thinking there has to be a better way. Anyone have any better ideas?

author: ajb
author_rank: Super Contributor
timestamp: November 29, 2021, 04:07:57 am
content: How many hundreds? There aren't a ton of connectors that take discrete wires and have more than a couple dozen pins, and need a certain amount of contact force so there's only so much that can be done to reduce the insertion force. (There are some headers for IDC connectors that have levers that help eject the connector, which might help though.) Can you rework the project to allow some of those hundreds of wires to go to different boxes so you're not so constrained? Like IO expander 'pods' that connect back to the main box with some sort of serial link with only a few signals?

author: james_s
author_rank: Super Contributor
timestamp: November 29, 2021, 04:23:42 am
content: Could you use several FPC cables? You can get those at quite large pin counts. They're a bit fragile though.

author: TomS_
author_rank: Frequent Contributor
timestamp: November 29, 2021, 09:29:48 am
content: Is something like RJ21 a workable solution? 25 pairs or 50 individual conductors.May not be the most dense solution, but would likely be a lot easier to disconnect and reconnect.

author: tszaboo
author_rank: Super Contributor
timestamp: November 29, 2021, 11:23:31 am
content: DIN 41612Standard has 96 connections on one connector. The connectors are cheap, and wire to board connector parts have shrouding, you can use multiple conductor cables, and so on. And it exists in flatcable version.

author: Ian.M
author_rank: Super Contributor
timestamp: November 29, 2021, 12:17:36 pm
content: Yes, DIN 41612 in its 3x32 format is one of the densest 0.1" pitch connector systems that are readily available. If the devices already have leadout wires attached, you can get DIN 41612 female crimp shells and contacts, which although a PITA requiring specialist tooling (i.e. a ratchet crimper with the correct die for the contacts and wire size, an insertion tool and a removal tool for your inevitable mistakes) is preferable to having to do wire to wire splices.Also for either ordinary 2 row IDC or DIN 41612, consider getting right-angle male connectors and mounting them at the board edge. It resolves the vertical clearance issue and provided you leave 'finger space' behind the ends of each connector, lets you use a two handed pinch grip to provide the insertion force, without bending the PCB. Another refinement for IDC connectors would be to mate them with latching box headers on the PCB not ordinary pin headers, as cams on the latch arms partially eject the cable connector when you fully open the latches, reducing the risk of damage when disconnecting.

author: CaptDon
author_rank: Super Contributor
timestamp: November 29, 2021, 02:06:55 pm
content: Hundreds of outputs??? Tell us more.......What would have hundreds of outputs, yet be inside a small constrained package? If each output controlled one leg of a bionic spider you would still have a lot of spiders and a shit load of wires. I love how the U.S. measures things, on the small end there is 'a boat load', then scaling up you have 'a crap load' and finally 'a shit load'. I have done some insane audio panels back in the days of snake cables and only ever made it to 'crap load' of wires and connectors. Cheers!!

author: stereodanny
author_rank: Newbie
timestamp: November 29, 2021, 08:27:11 pm
content: Quote from: james_s on November 29, 2021, 04:23:42 amI was thinking about exploring that—I could make a breakout board with solder pads and connect it to the main board via FPC. Like you said they are not very robust.Quote from: CaptDon on November 29, 2021, 02:06:55 pmI design LED displays with hundreds of individual LED arrays illuminating lightpipes. I'm trying to establish a design that removes as much work as possible and increases reliability, so I can get to the "creating" part, which means less time splicing wires, hopefully.Quote from: tszaboo on November 29, 2021, 11:23:31 amQuote from: Ian.M on November 29, 2021, 12:17:36 pmI think this is it! This is exactly what I was wondering about. I am impressed at how cheap they are too. Thanks

author: EPAIII
author_rank: Super Contributor
timestamp: November 30, 2021, 12:00:17 pm
content: I had to build a one-of-a-kind controller with a large number of connections once. It controlled a 6 meter satellite dish and a number of receivers used with it.I used standard ribbon cable with insulation displacement connectors ON BOTH ends of the cables. The individual breakouts were done on the circuit boards, not by soldering the wires in the cable individually.Yea, yea, I will bet you are stuck with with existing devices on the other ends of those cables. I would still think about designing some PCBs to do the breakout. You can at least use larger wire sizes for the individual connections if really needed. But you can probably design those loads into those PCBs.PS: Because that project was one-of-a-kind and that was several decades ago, I did not use PCBs. I used wire wrap and that can go faster then soldering if done right. And although the project was a one-fer, I did make spare circuit boards which all connected via the header connectors and ribbon cables so change-our would be easy in case of a failure.