DIY i2c cables


Hey All,

So im looking at running the new poly earthsea in my system, but my cases are split by design. My JF is in the top case and my Ansible, powered i2c busboard and 301 are in the bottom case. I know there is the txb in development but i was wondering if its possible to just drill my case and add a stereo jack to each and connect the cases that way? What would be the best way to wire this up?


Theoretically it could work. Since I2C is 3 pins, I think you’d just have to make sure the jack wiring matches up on both sides. You might have read up more on I2C around here than me, but my impression of it is that it’s not amenable to hot-plugging (particularly since one of the pins is ground), so you might have to take care there as well.


Thanks for the tip on hot-plugging, something I wasnt awar of. If I did go ahead with my idea it would be always plugged in. The case folds in half so I’d only remove it when traveling.


Made some i2c cables that seem to work great, thanks for all the info here!

I used and

I had some difficulty with applying pressure and broke 5 of the connectors in the process of building these. Needle-nose pliers weren’t a good fit for the job as they apply pressure at an angle. you need to be able to apply quite a bit of pressure to get the socket connectors to close on the wire. I ended up using the back of my multimeter and just trying to be careful to push directly downward.


I use an adjustable jaw pipe-wrench sorta thing. You want something with a wide-jaw with flat-ish surfaces on the inside…

Found something on amazon - they called these “water pump pliers”



at my hardware store I found a “crimp tool” that worked like a charm. I think I used the “wire cutter” bit.



I do have a tool like this, will try if I run into this again.


I have to connect TXb to ER-301 (i2c ready, I know I need a reversed cable), Just Friends – and later two Ansibles, when I can find any. I have two questions:

  1. If I use female-female jumper wires, how would I connect the headers in sets of 3? I assume heat shrink tubing, but which size should I order for this purpose?

  2. The TXb has pins in sets of 2 x 3. I think the rows are just in parallel, so I would use any 3 pin row for one connection?


Should these cable work as connectors between Teletype and Just Friends?

Thank you for your help!


Yesterday I fried a case’s power supply and a powered TT i2c backpack trying to set up a small system with TT i2c’d to JF and W/.

I’m fairly sure it fried because the TT backpack’s pins made contact with something inside of the case, but just to rule out all possibilities could it have been some problem with the i2c cables I had used?

the cables


those cables look totally fine.

shorting the pins on the backpack is definitely a problem. The SCL and SDA pins are 3.3v so it those touch ground that’s not good.

Best bet might be to pull everything from the case and check the voltages on the power supply. Then check if there are replaceable fuses or anything like that (Not too familiar with PSU designs).


Thanks for the reply.

Hearing that makes me feel a lot less scared to attempt this again.
I’m in contact with the case maker and am trying to see if it’s salvageable… At least none of the module’s seem to be damaged so feeling grateful for that.


FYI - I use 7/16 or 1/2 inch shrink tubing around the 1x3 connectors on F-F jumper wires.