[sdiy] PCB extenders with a flexible ribbon cable - looking for suggestions on construction method

Sat Feb 3 21:30:39 CET 2024

https://imgur.com/a/92ZLqvf

On Sat, Feb 3, 2024 at 5:23 PM Ben Stuyts <ben at stuyts.nl> wrote:

> Yeah, in the Netherlands I got this 😏:
> [image: PastedGraphic-2.png]
>
> On 3 Feb 2024, at 17:13, Mike Bryant <mbryant at futurehorizons.com> wrote:
>
> Well you've confused Google.  In the UK that shows the 2cent Euro coin :-)
> ------------------------------
> *From:* Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of cheater
> cheater via Synth-diy <synth-diy at synth-diy.org>
> *Sent:* 03 February 2024 15:24
> *To:* Ben Stuyts <ben at stuyts.nl>
> *Cc:* synth-diy <synth-diy at synth-diy.org>
> *Subject:* Re: [sdiy] PCB extenders with a flexible ribbon cable -
> looking for suggestions on construction method
>
> I guess this isn't easy to google, so here's the exact thing I mean:
>
> https://www.google.com/search?q=eurokopplung+&tbm=isch
>
> On Sat, Feb 3, 2024 at 4:20 PM cheater cheater
> <cheater00social at gmail.com> wrote:
> >
> > On Sat, Feb 3, 2024 at 4:16 PM Ben Stuyts <ben at stuyts.nl> wrote:
> > >
> > > You don’t mention the length of the cable, but perhaps some other
> possibilities are:
> >
> > between 10cm and 2m, usually 15-50 cm. Thanks for asking!
> >
> > > - rigid/flex pcb (but could be expensive depending on length of the
> tail, panelising will help here)
> > > - FPC cables (e.g.
> https://www.we-online.com/en/components/products/em/connectors/fpc_connector_and_ffc_cab/wr-ffc_flat_flexible_cable_0_50mm)
> >
> > I'm not looking for a connector! I already have one. I'm looking for a
> > good way of quickly and reliably soldering ribbon to a pcb, and I'm
> > also looking for an enclosure.
> >
> > > Consider 3d-printing the case.
> >
> > I did! It's mentioned in the OP. It's better to find something that
> > already exists. Currently I'm thinking about whether a cable mount
> > europlug receptacle will be good for that, it seems to have the right
> > dimensions, and i can just remove the mains related inner life.
> >
> >
> > > Ben
> > >
> > > On 3 Feb 2024, at 12:26, cheater cheater via Synth-diy <
> synth-diy at synth-diy.org> wrote:
> > >
> > > Hi all,
> > > I need to build a bunch of PCB extenders. Basically, they're two PCBs,
> > > connected with a ribbon cable. I have to build like a 100 or so. Both
> > > sides have gold finger PCB edge connectors, there is no slot on either
> > > side.
> > >
> > > I was wondering if anyone had suggestions on how to best do this to
> > > keep the cost, assembly time, and rejects to a minimum.
> > >
> > > The specs are:
> > > - The signals carried are up to 35Vpp, tiny current, sub-500kHz,
> balanced
> > > - Each pcb is 25mm wide (but can be a little wider) and can be
> > > anywhere between 10 and 80mm long. No logic, purely 1-1
> > > straight-through connection. They can have vias if needed, but
> > > hopefully not needed. Produced in a pcb house, not at home.
> > > - The card edge is on the 25mm long edge and the ribbon would be going
> > > out of the opposite edge
> > > - 32-36 pins need to be carried by ribbon. 32 is the minimum, but more
> > > is fine (I'd just carry ground)
> > > - The ribbon needs to be as flexible as possible. what is the most
> > > flexible ribbon you've ever seen? I'm looking to keep BOM cost down
> > > but if the thing is tough to bend like a stick then that doesn't help.
> > > Are more core strands better? Mouser lists a few stranding options:
> > > ones that start with 7 and ones that start with 19. The options seem
> > > to be: 7, 7x34, 7x36, 7x38, 19x40, solid. I assume the left number is
> > > the number of strands and the right number is the AWG. What's better
> > > here for flexibility? The cable isn't going to be moved a lot or
> > > strained, but up to 2 meters of it are going to hang off the
> > > connector. I assume higher AWG (=smaller strand diameter) is better,
> > > and more strands is better, but is 19x40 not going to be, in
> > > aggregate, thicker than 7x38, and therefore less flexible?
> > > - What sort of material should the insulation be made out of to be
> > > (and remain over a few, say 5, years) the most flexible? The options
> > > are: EPDM, PO, EVA, FEP, PFA, Polyester, PE, PP, PUR, PVC, TPE. Am I
> > > right to assume that PVC and Polyester are going to be the least
> > > flexible?
> > > - Are there tools that can strip all wires of a ribbon at once? Are
> > > they good? Are they expensive? Can someone suggest such a tool?
> > >
> > > Here's are some construction methods I was considering:
> > >
> > > Method 1. Take a ribbon that's been stripped and pre-tinned in a
> > > solder pot with 7mm bare wire sticking out. using a press, pre-bend
> > > the bare wires so if the ribbon is placed flat on a surface, the wires
> > > aren't "up in the air", and clip the leads to size (think something
> > > like the surface-mount leads of a QFP or something). The pcb has
> > > surface-soldering lands on it that will mate those 3mm bare wires.
> > > Take the pcb and lay the ribbon parallel with it, so the tips of the
> > > wires align with the pcb. However, the ribbon should go from that edge
> > > *towards the card edge connector side* which is "the other way" than
> > > you would expect. Then, you stick the whole thing in a solder pot, and
> > > after a few seconds, it's all soldered in place. Add a mechanical
> > > brace around the pcb+ribbon for retention. Finally, bend the ribbon
> > > 180 degrees so it's going in the right direction.
> > >
> > > Method 2. similar to above, but instead of using a pcb ribbon, use a
> > > hot bar soldering iron tip. Mount the soldering iron in something that
> > > looks like an arbor press, put the pcb and ribbon in, press down while
> > > feeding solder.
> > >
> > > Method 3. Everything's through hole, put the wires through the holes,
> > > and put the thing in a solder pot; add a mechanical brace.
> > >
> > > One thing that's kind of questionable is whether the pcb is wide
> > > enough to comfortably solder a 32-wire ribbon without microsoldering
> > > needed for bridge removal. If not, I considered putting the ribbon on
> > > a diagonal across the PCB.
> > >
> > > Do you think any of that would work? Which method is the best? If
> > > yes/no, what's necessary to make it work better? Does anyone have
> > > better suggestions?
> > >
> > > Finally, I'd have to find some sort of enclosure. Basically, I'm
> > > trying to make something that will look like the "cartridge" in this:
> > >
> > > http://devkits.handheldmuseum.com/IS-CGB-EMU/index.htm
> > >
> > > ...but obviously I'd need some sort of cartridge casing. I'd prefer to
> > > buy something that's ubiquitous and can be repurposed for what I'm
> > > doing. Sadly gameboy cartridges are just too wide for my use, at 60mm
> > > (vs 28-30mm being perfect), and I'd like to find something thicker
> > > because I'd like to fit the ribbon inside them for mechanical
> > > retention. I considered DB-15 connector back shells, but they have
> > > those "wings" on the side that the mounting screws go through which I
> > > guess I would have to cut off or something, plus idk if these cases
> > > would be easy to mount a pcb in. 3d printing is an option, but I'd
> > > really like to avoid it, given the cost + maybe they're not as
> > > mechanically durable (it's a connector after all). Essentially i'm
> > > kind of looking for something shaped like the rectangular container of
> > > a PEZ dispenser, so I'd welcome suggestions. It's fine if I have to
> > > lop off one of the sides to make an opening.
> > >
> > > Also, after assembling the extender, I guess it would be nice to have
> > > a test harness (pass/fail on all signals indicated by LEDs plus
> > > per-wire LEDs).
> > >
> > > PS does anyone know why PCIE slot connectors (like on motherboards)
> > > have those slanted "rasps" on one side? Always found that weird. What
> > > are they for? Some sort of retention mechanism? Curious.
> > > ________________________________________________________
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>
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