Use & Power 128 x 128 OLED Display with Conductive Thread

Hi all,

I am looking to connect 3-ply conductive thread to the GND, Vin, SCK and Data pins (I2C mode) of this 128 x 128 px grayscale OLED by Adafruit:
Grayscale OLED

Board: Teensy 4.0
OLED: SSD1327 Grayscale

The constraint is that I need this whole thing to go into a wearable (hoodie), so it should be as slim and low-profile as possible.

I am looking to connect as much as 4 feet of the thread, and I understand that there is a certain resistance per foot for the thread of about 10-16 Ohms that could be limiting the current that the OLED requires.

I have already tried what I'm describing (connecting the thread to the OLED), and the results were unsatisfactory: OLED power light turns on, SSD1327_test.ino successfully uploads and Serial confirms that the display has initialized. Sadly the display shows a blank screen, but when I use jumper wires it lights up and performs the test.

I'm thinking I could find a way to boost the current travelling through the wires,

OR

Use a different material than the thread,

OR...

You tell me!

Any guidance, questions, concerns, comments, advice, expertise, help greatly appreciated.

Thanks!

How about stitching the conductive thread in a stitch that incorporates multiple threads, so that the threads are shorting each other out and so reducing the resistance. Try it for power and ground, the signals should be OK.

This is a picture of a Rope Stitch, but there are many other stitches like a Wheat Stitch that could be used. The stainless steel conductive threads, I think, are your best bet.

If you want an alternative then you can use a thin and very flexible length of microphone cable.

It can be stitched against the cloth so that it flexes with it.

This is one I have used a lot for thin flexible connections.

Audio Screened Cable

Hey Mike, thanks for the great suggestions. I’ll definitely look into the rope stitch techniques.

I am thinking of stitching magnetic wire (28 AWG) coated with an insulating enamel, then sewing an interfacing layer of neoprene over it for further insulation.

Since the wire is copper and protected from oxidization, current should flow pretty well.

If this thought process is erroneous, please lmk!

Thanks again,

-D

The worry I would have with this is that repeated flexing of solid copper wire is prone to fracturing due to metal fatigue. Solid wire should only be used when the wiring is going to be undisturbed once the initial construction is finished.

I would assume that is not the case with a wearable. Look at the wire I linked to, it is only thin but is multi stranded. You get a potential fracture point when you solder it where the wire makes the transition to soldered. This is where putting a strain relief helps because it stops the transition point from bending. You can use hot melt glue for strain relief.

The best solution however is to use a crimped connector into a pin.

Okay. I am going for super thin, in eventual hopes to cross the gap between wearable gimmick and actual product.

I am looking into Litz cable used for high-speed radio communications. It is described as flexible, stranded, copper, insulated, thin, and also is less affected by electromagnetic fields. It would not be stitched directly to the fabric, but rather fed in between a 2-layers sleeve of stretchy insulating fabric stitched to the inside of the hoodie.

So far, this sounds like it would work, and the wire that I'm looking at is 30-strand at 30/38 AWG.

If there is an objection to this idea and thought process I am all ears!

Thanks for your suggestion,

-D

Have you ever handled Litz wire? It is a nightmare.
The individual strands are wrapped in a spiral cotton cover, and is almost impossible to solder to. This is because any application of the soldering iron chars the cotton and makes the wire imposable to solder.

Not to put you off or anything but I have not had any great success when I have encountered it.

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