Ohm Hook - a Vibrating Resistance Meter for Crochet

This crochet hook translates electrical resistance into vibration, making electrical resistance a tangible property of an E-Textile making process. The Ohm Hook allows you to develop an electrical sense for the materials you work with. For example, if you are crocheting stainless steel yarn to make a stretch sensor you can tailor your design to the range of resistance you want because you immediate feedback on the resistance of what you are making.

The Ohm Hook is made by cutting and stacking pieces of clear acrylic, and sewing them together with thick thread. The circuitry is contained within the layers of the acrylic and remains visible. To use as few elements as possible, I sought to use materials for both their electrical and material/mechanical/aesthetic properties. For example, the shaft of the crochet hook is itself the negative lead to the coin-cell battery.

The following Instructable explains the steps I went through to make the Ohm Hook, and was made during the Instructables Artist in Residence at Pier 9.

This design is an iteration on the Vibrating Crochet Hook Instructable that I made in 2011.

MAKE TOOLS, NOT PARTS

The Ohm Hook is part of a series of Tools for E-Textile Techniques that are motivated by a desire for MORE tools and LESS parts when it comes to building electronics. So many electronic functions are compartmentalized into discrete parts. These parts make up the tool-set of most engineers/designers/makers who build electronics. And while they make it easy and fast to prototype and build electronics, these parts also end up defining and constraining how we make and what we can build. By making tools that allow us to create our own parts, I hope to encourage a greater electronic diversity. Also see the Tools We Want project for more such ideas.

MATERIALS

- 3mm thick clear acrylic

- crochet hook with 3mm diameter shaft

- vibration motor

- CR2032 coin-cell battery

- solderable conductive thread (Karl Grimm)

- cotton thread

- pin

- crocodile clip

TOOLS

- laser cutter

- sand paper

- cutter knife

- soldering iron

- sewing needle

- scissors

Before creating my design in Illustration, I like to trace an outline of the parts I will use onto paper and start to sketch ideas for where things go and how I want things to look. Attached to this step you should be able to download the vector file (STL) that I used to lasercut the handle out of 3mm clear acrylic.

The cut and engrave settings I used on a 75 Watt Epilog were the following:

CUT

Speed: 25

Power: 65

Frequency (Hz): 5000

RASTER/ENGRAVE

Resolution (dpi): 1200

Speed: 73

Power: 73

After cutting some of the acrylic is stuck in the holes but you should be able to easily snap them out with a needle. Also wipe off any residue with a tissue or scrap fabric.

To give a mat finish to the acrylic, sand it gently with some medium to fine sandpaper. I used 400 grit.

To make the vibration motor "sewable" we're going to solder to leads of conductive thread to the contacts in place of the wires. Scrape off the material protecting the solder joints (and also any double sticky tape that might be on the back of the motor). Then de-solder the leads and re-solder two pieces of conductive thread.

The motor should sit perfectly in the lasercut hole with the solder points sitting snug in the engraved recess. You can tin the tips of the conductive threads to make them more easily sewable. Begin sewing the conductive threads in and out of the holes. One thread will end at the coin-cell battery cut-out and form the contact to the positive side of the battery. The other thread will end at the tip where there is an engraved dot.

Wrap the thread ending at the battery around the inside of the coin-cell cut-out and then solder it back to itself. Then cut the thread close to the solder joint.

The thread ending by the engraved dot needs to connect to a pin that will go between the dots on both outer pieces of acrylic. Insert the pin through the fibers of the thread and then solder it in place. Clip the needle so that it is only as long as it needs to be to be held in place by the two outer layers when they are sandwiched together.

Now it is time to sew all three layers together. Thread a needle with the thick cotton thread, then stack together your layers. Make sure the holes line up and the pin is in place. Push the needle through the holes of all three layers and continue sewing around. When you get back to where you started, continue sewing alternating stitches to look like in the photos. When finished tie a double knot and cut the threads short.

Check that a crocodile clip and connect to the pin.

To insert the battery press it into the cut-out. To take the battery out, use the hook to lever it out from the tab.

Some nice photos of the transparency of this design.

Here are some photos of the four tries I made leading up to the final design.