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Electronics => Repair => Topic started by: KaneTW on March 22, 2019, 08:34:28 pm

Title: Low-profile, 2.54mm connection between two boards
Post by: KaneTW on March 22, 2019, 08:34:28 pm

I'm replacing a LCD on a home appliance with a new one. Since the appliance is pretty old, the original LCD is unavailable.

The original LCD has a through-hole pin header that mates into a SMD receptacle on the main board, with a total clearance between the two PCBs of about 3-4mm. Increasing that distance would make some buttons on the main PCB unpressable.

Now the new LCD also has a 2.54mm pin header footprint (unpopulated), but it's offset by about 5mm vertically. There's not enough space to just shift the entire LCD.

Any ideas on how to connect these?

Some pictures here (gallery): https://imgur.com/a/oOGxAb0

Title: Re: Low-profile, 2.54mm connection between two boards
Post by: T3sl4co1l on March 22, 2019, 08:50:48 pm

Oh no worries, those are plenty available. Shop for bottom-entry, SMT female headers/sockets.

Tim

Title: Re: Low-profile, 2.54mm connection between two boards
Post by: KaneTW on March 22, 2019, 09:16:23 pm

There's already one of those on the main board. The problem is the offset between the existing LCD's header and the new LCD's.

Title: Re: Low-profile, 2.54mm connection between two boards
Post by: LateLesley on March 22, 2019, 09:20:18 pm

I think in that situation, i'd just use ribbon cable, and solder between the two boards, leaving a little extra ribbon for manoeuvrability,, and so you can fold it flat, level with the PCBs. It's about the easiest way I can think of. Maybe others will have a better suggestion. 

Title: Re: Low-profile, 2.54mm connection between two boards
Post by: wraper on March 22, 2019, 09:20:28 pm

Replace female connector on PCB with male connector. If space allows, solder male connector on LCD as well and connect boards with cable which has female connector on both ends. If space does not allow it, solder cable on LCD end directly to PCB.

Title: Re: Low-profile, 2.54mm connection between two boards
Post by: KaneTW on March 23, 2019, 12:20:31 am

Good idea, and probably what I'll go with. I've been trying to find a low-profile ribbon cable connector (cable -> socket) but the best I found was Samtec ICSD at ~9.5mm height. Probably going to have to make do with that.

Most likely will have to solder the cable to the LCD, but that's not too big of a deal.

Title: Re: Low-profile, 2.54mm connection between two boards
Post by: T3sl4co1l on March 23, 2019, 08:56:17 am

Oh, so the socket is the main board, and the header is the LCD?  Ah, so then the last picture is comparing old and new?  (This would've been more obvious with captions..)

Yeah, you aren't going to find something commercial to shift the centers.  Best bet, interposer board, with SMT pins (could use an SMT header and pry off the plastic body after soldering), and the LCD connections will have to be SMT pads, soldered through the header holes (the solder equivalent of a plug weld joint).  Barring that, just wire it one at a time, ribbon cable would be alright, or loose wires.  Preferably thinner wires (28ga wire wrap style?) so it doesn't get too in-the-way.

Bonus points for wiring to a header, as a top-side plug?  Mind the reversed pinout of course.

Tim