Paint and Play Serial Port

[knc1]

The target audience are those who will be connecting a serial port to their Kindle motherboard perhaps once in a life-time.

In this thread, I try to use common, low cost, materials.
Things which might even be useful for their intended purpose.

• Photo #1 - the "paint and play" kit.
  This will be a DIY conductive ink type of connection.
  There are many sources of (usually expensive) conductive ink, but my intended audience only needs three or four drops of it.
  And they probably don't have any use for the left-over ink.
  So here we will make our own.
  • DIY conductive ink
    • Extra fine graphite - such as for locks - auto supply, hardware store, etc.
    • Gloss Black Acrylic Paint.
      Note: The recommendation I read was for Black Acrylic INK, but my local hobby-crafts and artist supply store was sold-out.
      So here's hoping the black pigment in acrylic paint is as conductive as the blank pigment in acrylic ink.
  • Mix and apply tools
    • Small plastic mixing containers (bottle caps here).
    • Mixing tools (toothpicks)
    • Smallest Artist's paint brush you can find.
  • Serial port wire and materials
    • 30 gage, insulated, wire-wrap wire. Any insulated, 28 ... 32 gage wire will do.
    • Low residue tape - I.E: "Painter's tape"
    • Pin vise - as a handle for the forming tool (optional)
    • Forming tool - sewing machine needle (a regular needle would do)
  • Our test jig
    This is the goal of this first post, make the ink, apply it between two wires, measure its conductivity to see if our DIY ink will serve our purpose.
• Photo #2
  The Kindle motherboard is fiberglass PCB covered with a solder mask.
  The test jig is a PCB covered with a solder mask. The point is to check materials compatibility as we build our painted connection.
  Also one stripped end of the wires we will be using.
• Photo #3
  We need to bend a small hairpin loop in the ends of our wires.
  The wire used, and shown in the prior photo, is 0.010 inch (0.255 mm) in diameter. So having a tool to bend it with is nice.
  This is a sewing machine needle, because the shank is large enough for even human sized fingers to hold and roll.
• Photo #4
  One of the wire leads with a (sort-of) nice hairpin loop in the end.
  You can see the "bump" left from my first try to bend it, and then straighten it out again.
  The scale of things we are working with is the reason for the "forming tool".
  Just doing this with your fingers is possible, but can be tedious.
• Photo #5
  The second wire, with a sloppy hairpin hook formed, held in place with some "temporary" type of tape.
  Well back from the end.
  You will notice that the hairpin hook does not want to lay flat on the board. We will take care of that RSN.
• Photo #6
  The two hairpin hooked ends of the wires, positioned and held in-place by the "temporary" tape off-screen to the right and left.
  Note that the hooks are not (yet) flat to the board.
• Photo #7
  Tape the hooks flat to the board, leaving room between this piece of tape and the two other pieces of tape holding the wires in-place.
• Mix up your hold-down glue
  Not shown as part of the "kit", but I use 5-minute Epoxy. Other stuff might work, but this is what I am familar with.
  With the plastic (tiny) mixing bowl, mixing sticks, mix up a bit of the two-part, Epoxy resin.
• Photo #8 and #9
  Place a hold down drop of the Epoxy on the right and left wires.
  Each drop goes between that center piece of tape and the outer pieces of tape.
• Photo # 10
  After gently removing the "temporary" tape, gently I say, so as not to pull the hook ends of the wires away from the board, you can see the wires now positioned and held in-place.
  Notice that the wires are close enough to the board that the Epoxy "wicked" along the wires.
  Sorry about the funky lighting.
• DIY conductive paint
  Put a few drops of the black paint into one of the mixing cups.
  "Puff" a small amount of the graphite onto the paint.
  Mix.
  Repeat as required.
  Your trying for a very heavy liquid to a light cream.
  If you add too much graphite, it will "clump" - so your close at that point - just add a few drops of the paint at a time and stir to a light weight cream.
• Photo #11
  Using that tiny paint brush, span the two ends of the wires with a line of the DIY conductive paint.
  The brand shown in the kit picture can be "cleaned up" (corrected) with water before it dries.
  Allow to dry (the brand shown claims 1 hour).

Alright - the bottom line - did we make a painted-on, resistor?
Yes - this one measures 790 ohms.

Keep in mind the electrical/electronic use of our DIY conductive paint:

The test strip is much, much, longer than what we need to connect the wires to the serial port connection solder dots.
So in our use, the connections will be much less than that 800 ohms.

In our use, the hairpin loop of the wires will be positioned so that the solder dot is on the inside of the loop, right up at the curve.
So our DIY conductive paint length will be hardly longer that the thickness of the wire (0.010 inch, 0.255 mm).

PLUS:

These are CMOS ports - they would work just fine even with 10,000 ohms in series with them (in fact, the motherboard has series resistors already in the connection trace for noise reduction).

YUP - It works.
Now go free up some locks with the left over graphite, touch up something with the paint, and maybe even repair something with the left-over Epoxy.

All low cost items, all of the left-overs can be used for something.

[knc1]

KT-2 Serial Port reference materials, see:
https://www.mobileread.com/forums/sho...20&postcount=3

[knc1]

Next, in the above (second post) -
I see if I can ruin my brand-new KT2 by following my own directions.
Coming to this thread RSN.

[LastSilmaril]

So in the final analysis, is it more or less work to make this paint and test it than it is to practice microsoldering enough to be competent?

[knc1]

Originally Posted by LastSilmaril

So in the final analysis, is it more or less work to make this paint and test it than it is to practice microsoldering enough to be competent?

Less
By a few years and no special (expensive) tools.

Plus -
Get a glob of hot solder in the wrong place might be an error that you can never recover from -
With this, make a mistake, wipe it off with something (q-tip?) wet.
You can't do wet clean-up and correct with hot solder.

[brianinmaine]

I like the home made conductive paint, but some might rather try conductive paint in a pen? http://www.ebay.com/bhp/conductive-pen
Could you also use the paint to fix rear window defoggers from an auto parts store? http://www.ebay.com/itm/Loctite-2135...cb66d0&vxp=mtr

[knc1]

Originally Posted by brianinmaine

I like the home made conductive paint, but some might rather try conductive paint in a pen? http://www.ebay.com/bhp/conductive-pen
Could you also use the paint to fix rear window defoggers from an auto parts store? http://www.ebay.com/itm/Loctite-2135...cb66d0&vxp=mtr

Yes to both.

But they miss my target audience on two points:
* Price
* Lots of left-over that can't be used for anything other than making conductive traces.

The left-overs from my suggestion can all be used for their original, intended purposes.

[knc1]

Ignoring my price and re-usablity points - -
This one looks like fun:

Words and pictures:
http://spectrum.ieee.org/geek-life/h...conductive-ink

One (USA) on-line source for the metals:
http://www.mcssl.com/store/gallium-source/gallium-metal
http://www.mcssl.com/store/gallium-s...--indium-metal
(It looks like a minimum amount is around $50)

Mid-page, a chart of various tri-metal combinations:
http://sci-toys.com/scitoys/scitoys/...uid_metal.html

So if someone has the $50 .. $100 to spend, and tell us if the ink beads up or flows on top of the Kindle's solder mask ...

The required video: