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Step 3


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Building North Paw V1.0
Step 3: The Display

Back to step 2: EnclosureForward to step 4: Final Assembly

During this step we’re building the North Paw’s haptic “display”. This display consists of eight vibrating pager motors attached one by one to a length of ribbon cable and mounted on a Veltex foam backing. You’ll need:

Supplies (incl. in kit)

  • 8 pager motors
  • 10 inch strip of Veltex foam
  • 12 inches of ribbon cable
  • Extension wire (for any pager motors with shorter wire leads)
  • Shrink tubing
  • Strip of sticky back hook Velcro.
  • Square of soft, thin fabric.

Tools (not incl.)

  • Soldering iron
  • Wire cutters
  • Wire strippers (recomended, but wire cutters can work if you’re careful)
  • Heat gun (recomended for shrinking the shrink tubing, but soldering iron can work too)
  • Scissors

This is the most difficult part of the kit! It is quite concievable that you could snip the wrong wire at various points in the procedure, so please take your time and be careful.


To get things started, place the strip of veltex flat on the table. On top of that, space the eight motors out evenly. The motors won’t be affixed to the veltex until the end of this process, but having them spaced out on it will be a handy length reference as you cut the ribbon cable.

Once the motors are spaced evenly on the fabric, take note of how long their wire leads are. You might have eight motors with long leads (congrats, that saves you a couple steps!), or you might have eight with short wire leads (sorry!), or even a combination. If you have any of the motors with short wire leads, you will need to cut some extension wires from the length of wire included in the kit. Now is a good time to do this, so cut as many extension wires as you have motors with short wire leads, less the last motor. In this picture I have 4 long wire motors and 4 short wire motors. There is 1 short wire motor at the end which doesn’t need an extension wire, so I cut just 3 extension wires.

These extension wires should be just about one inch long. While you’re at it, go ahead and strip the ends of these wires. You should have a bit of extra wire in case you mess up, but not too much so be careful!
Now you need to start seperating the different strands of the ribbon cable. The easiest way to do this is to get your wire cutters in between two strands and gently snip the insulation. You only need to snip a milimeter or two, after that you can peel the strands apart by hand.

With the red wire on top snip below the third strand.

A brief explanation: The first (red) strand will be the common power line for all the motors. The thrid strand is the sink for the first motor which will be turned on or off by the controller. If you were making a belt with more than eight motors the second strand would be a second power line, but you’re only making an 8-motor anklet, so just leave the first three strands together for now.

Next peel back the lower seven strands until just to the right (2-3mm – it doesn’t need to be super exact) of the next motor.

Cut those seven strands there.
Now seperate the fourth strand from the next six strands. Peel back until just to the rigth of the next motor and cut again. Continue in this fashion to the left, peeling and cutting each strand in turn. When you’re done, each strand will terminate just to the right of each motor.

If you have all short wire motors
Peel each strand away from the rest of the ribbon cable so that there is about 1.5 inches of wire

If you have all long wire motors
Peel each strand away from the rest of the ribbon cable so that there is about 0.5 inches of wire

If you have a combination of short and long wire motors
Peel each strand away from the rest of the ribbon cable so that there is about 1.5 inches of wire and then snip the wires down to 0.5 inches where there are long wire motors. (See three images below.)

Sorry if this confusing! It’s important to ensure that the spacing of the motors ends up even in the end.

Strip the insulation off of all of these wires. For the end two, it might be helpful to cut the second (no connection) strand to keep it out of the way.
Tin everything in sight. To tin, all you need to do is heat up the exposed bit of metal wire and melt a little solder over it. Don’t worry if it seems that the pager motors’ little tiny wires aren’t picking up too much solder. Also, make sure not to forget to tin both ends of any extension wires you cut.
You’re almost ready to start actually soldering things together! But, you’ve got to get the shrink tubing on before soldering, of course. Now’s the time to cut a bunch of 1/3 inch pieces of shrink tubing.

The number of pieces you need will depend on the number of short wire motors you have: cut 1 piece for each long wire motor, cut 2 for each short wire motor, and cut 2 for the last motor at the end, regardless of whether it’s short or long. I have 4 long and 4 short, with one of those short ones at the end, so I need 12 pieces of shrink tubing.

Making sure to put the shrink tubing on first, solder up one lead of each motor to each exposed strand of the ribbon cable. If you tinned everything properly, this will be as simple as holding the exposed ends of the two wires together and heating them up with the tip of the soldering iron. As soon as the solder on the to wires melts together, slowly remove the iron. Wait a second or two before letting go of the wires – if you let go too soon, the solder will not yet be solidified, and the wires won’t be stuck together yet.

These DC motors are non-polarized, meaning it doesn’t matter which lead of the motor you solder up now. That being said, if you solder the red lead, the little bit of adhesive on the motors will be facing a more convenient direction later. It’s a small point, so don’t worry about it too much.

On the very last motor, go ahead and solder the second lead to the red (power) line.
On any short wire motors, solder on the extension wires now. You don’t need to put the shrink tubing on before soldering this time of course, but it’s probably a good habit to do so anyway.
If you are lucky enough to have a heat gun, go crazy shrinking up all that tubing over the solder joints.
If you don’t have a heat gun, you can shrink the tubing with the soldering iron. But, don’t go crazy! Gently slide the barrel of the iron across the shrink tubing. DO NOT use the tip of the iron, as this can have the unfortunate side-effect of melting the solder under the shrink tubing, ruining a solder joint which you now can’t see because it’s under the shrink tubing. Fixing that is always a pain.
Don’t despair, you’re almost done! There just one tricky bit left.

Take each motor and line up each free lead against the red power line. Where the end of that lead meets the power line, you need to trim off the insulation without cutting the whole wire. That’s it, that’s the last tricky bit.

The best way to do this is to take a number of small, gentle cuts at the insulation with your wire cutters. Once a tiny bit of the metal wire is exposed, stop cutting away and instead use the sharp edge of the cutters to scrape a bit more insulation away. After that it can also be helpful to pull at the side of the opening to widen it slightly. If you do accidentally cut the whole wire, don’t worry! Just solder it back together.

Another slightly different method (which you might find easier) is to separate the top wire from the rest of the wires in little chunks where to need to solder to it. Once the wire is not so close to the others it’s much easier to strip, and also to resolder if you happen to cut the whole wire. In fact, one way to accomplish this is to deliberately cut the top red ribbon wire, peel it back a little both ways, strip the two ends, then solder it back together along with the motor wire. A little electrical tape when you are done will prevent it having a spot which might catch when you put it in the armature.

You should now have seven exposed sections of the first strand of the ribbon cable. Tin them all.

Solder the other lead of each motor to these exposed sections. Congratulations, the hard part is over! You’re really, really good at soldering by now, for what it’s worth.
The motors now need Velcro backing so they can be adjustably affixed to the Veltex strip. So, the next step is to cut the long thin strip of sticky-back Velcro into 8 equal pieces. The motors will be sandwiched between these Velcro squares and some thin, stretchy fabric, so take the bit of fabric included in the kit and cut that into 8 equal squares as well.
Take the little bits of paper off of the motors to reveal their own adhesive side. Keep that side up. Take the paper off of one of the Velcro squares, lift up one motor, and then push the motor down into the middle of the sticky side of the Velcro square. Finally, grab one of the fabric squares, and place that on top. Push down hard all around the motor so the fabric adheres really securely.
You have lots of extra fabric, don’t you? This is what you needed the scissors for. Trim away. You can even trim off some of the Velcro, just don’t cut any wires!
Stick the motors onto the Veltex strip (the Velcro will only stick to the soft side of it). Space them out evenly, then fold the ribbon cable behind it .
If it looks like this, you’re done! And don’t worry, final assembly is about one fifth as many steps as this was, and there’s absolutely no soldering.

Back to step 2: EnclosureForward to step 4: Final Assembly


North Paw V1.0, for help contact eric@sensebridge.net

First published July, 2009


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