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finding the right connector for I2C

A project log for LAMEBOY - another ESP12 handheld

fully portable ESP12 project with battery charging and power muxing

davedarkodavedarko 11/17/2017 at 10:3419 Comments

The whole reason I'm looking for something else: I wrote seeed studio about getting the SMT version of the grove connector and they told me that they're sold out / not in stock anymore. I tried a JST 2mm 4 pin connector, but it's just a pain to connect. To be continued, but please, feel free to comment ideas. I need to find a connector that is: 


USB

there's already a usb port on the LAMEBOY and I don't want people to mixup stuff


TRRS 

would be nice, but I don't want to short stuff by accident or have users mistake it for the headphone plug - especially if there's no audio on board. 


RJ12 / RJ25 / RJ10

that was actually already proposed to me in a twitter comment () use the same stuff that LEGO, http://wiki.makeblock.cc/index.php?title=RJ25_Wiring_System and probably others. So right now I'm leaning towards RJ10, a 4P4C cinnector, that is also used to connect phones to the speaker+mic part.


MOLEX / 2.54mm connectors

Down in the comments Molex adapters and CD rom cables (basically 2.54mm headers) were suggested, I like the hacker-ready approach, but it doesn't feel like a "finished" design that I want to achieve with revision 4. The current boards have the grove connector still on them.


Sparkfun QUIIC connectors

@Patrick Van Oosterwijck suggested https://www.sparkfun.com/products/14417 sparkfuns QUIIC connectors, 1mm JST connectors - a wee bit too tiny and the same problems as bigger JST connectors. BUt it features a lot of sensors that one could use.


Spring connectors

another suggestion from twitter, use spring connectors. interesting, easily plug and play ready and probably accepts pcbs, if done right. using pcbs as connectors is the cheapest thing I can think of :D https://t.co/taDxle3lOT

Discussions

danjovic wrote 11/18/2017 at 00:16 point

How about a WII nunchuck connector? It is I2C already and can be done on the board, no parts involved. You can even use a nunchuck controller for some games :D

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davedarko wrote 11/18/2017 at 15:35 point

probably tough to source though and cables aren't that easy to get.

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Franck GALLIAT wrote 11/17/2017 at 16:25 point

maybe you could try good-old audio cable for CDROM drives (it had 4 pins 2.54 female-female) and generally only 3 wires (red, white, black) you could plug SDA,SCL,GND ... ?

as an example : http://www.cableleader.com/18in-mpc-4-cd-rom-audio-cable.html

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Franck GALLIAT wrote 11/17/2017 at 16:10 point

maybe you could try good-old audio cable for CDROM drives (it had 4 pins 2.54 female-female) and generally only 3 wires (red, white, black) you could plug SDA,SCL,GND ... ?

as an example : http://www.cableleader.com/18in-mpc-4-cd-rom-audio-cable.html

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davedarko wrote 11/17/2017 at 16:29 point

that's probably the same like ajlitt mentioned below, like a molex connector (maybe without the hook)

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Franck GALLIAT wrote 11/17/2017 at 16:33 point

it's the same system effectively (sorry for redundance), the only advantage of CDROM cable is that connector + cable is very easy to find... but ok

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davedarko wrote 11/17/2017 at 16:38 point

I'm more confused by the second comment, that is the same as the first :) but don't apologise, it's just brainstorming and technically something different.

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jaromir.sukuba wrote 11/17/2017 at 14:26 point

Or perhaps mini-DIN connectors, once commonly used as PS-2 connectors in 6-pin variety. There are 4-8 pins IIRC, so you can choose other pin count to minimize "user interferences".

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davedarko wrote 11/17/2017 at 16:37 point

might feel a bit big because of the height and I guess there aren't so much point to point cables for connecting modules with the same connector though. But still, good call :)

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jaromir.sukuba wrote 11/17/2017 at 19:38 point

Yes, it's a bit bigger than RJ-11, for example. I'm just throwing random ideas at you :-) I battled this problem on all my portable computers and found exactly -wait for it - zero solutions. Available connectors are either:

1, Already used (or purposely built) for something (USB, HDMI, RJ45), but small and rugged.

2, Rugged and suitable for generic use, but too big (Cannon, DIN)

3, Small, suitable for generic use, but not rugged enough for daily use (all sorts of pinheaders, edge connectors)

You have connector that is small-rugged-generic, but you can choose not more than two at once. I think this call for connector is similar to your call for keyboard, where you have a few different options and all of them wrong, or at least full of compromises.

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davedarko wrote 11/18/2017 at 15:37 point

I appreciate you throwing things at me :) it definitely looks like the call for a keyboard :) I should get one or two of the blackberry keyboards that @WooDWorkeR uses, btw. 

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davedarko wrote 11/17/2017 at 14:15 point

Almost normal dupont / 2.54mm pins, hm kinda working and also highly "hackable" because you can use breadboard stuff. but also look a bit unfinished, can't say why but it doesn't work for me.

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ajlitt wrote 11/17/2017 at 14:48 point

Yeah, a backshell would be nice to pretty it up.  There's no strain relief with that sort of connector, so the signal wire crimps are the only things holding it together.  Best I can think of is to use glue lined heat shrink between the back of the connector and the cable.

If RJ11/RJ12 won't work because of confusion with POTS, how about MMJ: https://www.digikey.com/product-detail/en/stewart-connector/940-SP-3066R-OST/380-1238-ND/2257010 https://www.digikey.com/product-detail/en/stewart-connector/SS-6466-NF-OST/380-1314-ND/2257320

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ajlitt wrote 11/17/2017 at 15:01 point

What about abusing a SATA connector?  It's relatively low profile, keyed, and cables with latches and overmold strain relief are cheap.

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davedarko wrote 11/17/2017 at 16:35 point

sata is 7 pins, but I like the size and availability of cables! In terms of confusion I think it's a bit more problematic than 4P4C / RJ 10, but it ranks high, thanks!

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ajlitt wrote 11/17/2017 at 17:46 point

SATA is capacitively coupled so it shouldn't destroy the Lameboy or the SATA device if someone does confuse the two.

The other thing is considering how much volume the connector adds to the Lameboy.  Right angle SATA and alt-USB are low profile and shallow, while RJ*, DuPont, and TRRS take significant PCB space or height.

If you can find the Wiimote PCB mount connectors, that would be ideal. The Wiimote carries 3.3V power and I2C.  And there are prefab controllers out there already...

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jaromir.sukuba wrote 11/17/2017 at 12:36 point

Just throwing random idea:

Maybe you can find some older weird USB connector, like 4-position USB mini B. There were a few very seldom used and nowadays almost nobody uses them, so there is small to none chance of interfering with real devices. There could be a problem with sourcing the connectors, though. It has 4 pins as you need and it you keep connection of 5V (insert schottky diode in series to prevent "backcharge") and GND pins, it will not break everything if you actually connect valid USB peripheral. It is also smaller than RJ11.

When going the RJ11 route, don't forget somebody can plug it to telephone line. You can't do totally foolproof design. Just can't. Never.

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davedarko wrote 11/17/2017 at 14:17 point

I thought about those too, but I think it get's tricky to buy cables then. Right now RJ10 seems nice. I've ordered some sockets in RJ12 / RJ25 size and RJ10 to get a feeling for the size and relations. Maybe 

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