Wednesday, June 20, 2012

Make Conductive Rubber: Transparent stylus-iPod/iPhone

Make Conductive Rubber: Transparent stylus-iPod/iPhone

I call it Oogoo II. It is a DIY conductive silicone rubber that can be used to create a transparent stylus for iPod, iPhone, iPad, and other capacitive screen smart phones. Because the contact part of the stylus is transparent, you can see your lines and draw more precisely than with a regular stylus.

This instructable shows how to make conductive rubber and use it to create three types of stylus:

1 Hack any pen or pencil and turn it into a standard type stylus for pressing keys or drawing sketches while still allowing it to write on paper.

2 Use conductive rubber as a flexible glue to make a transparent flexible round tip stylus for precision use in drawing and key pressing.

3 Use conductive rubber to make a flat transparent paint brush tip stylus for use in drawing and paint programs. It fits in a wallet

The intro pic shows the paint brush style drawing a line on an iPod.

Step 1Materials

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The step 1 pic shows the different types of stylus that can be made using conductive rubber.
The thumb pic shows most of the main materials used


Paraffin or candle wax

Naphtha solvent from hardware store

Silicone Caulk from hardware store

Corn starch from grocery store

Carbon Graphite powder- Available in larger quantities from:
Available in smaller quantities at your local hardware store. It's called lubricating graphite and comes in small tubes or bottles.

VeilSheild conductive fabric from:
Also shown is a nickel plated fabric that is no longer available.

Mixing cup

Popsicle stick

Pen or Pencil

Small diameter brass or metal tubing or rod from:

Step 2How It Works

Oogoo II-A Conductive Rubber
You can make your own conductive rubber from silicone caulk, corn starch and graphite powder. This creates a silicone rubber which can be made thin enough to paint on or thick enough to cast into molds. While it is not as conductive as wire or conductive thread, it is more than conductive enough to make a variety of capacitive stylus.

Capacitive Stylus
The standard stylus for a capacitive screen uses conductive rubber or conductive foam to replace your finger on the screen. Every persons body has a small capacitance. When you touch a capacitive sensitive screen, you change the capacitance where you touch. Such screens are designed to detect changes in capacitance and locate exactly where they are on the screen. When you hold and touch a conductive stylus to a screen your capacitance is transferred to the screen and detected by its sensors.

Transparent Stylus Tip
Two of the stylus made in this instructable use VeilSheild conductive fabric as the stylus tip. Because this fabric is 70% transparent it allows you to see exactly where you are touching the screen. The conductive fabric is glued to a conductive metal handle which transfers the bodies capacitance to the screen.

Step 3Making Conductive Rubber

Mixing Oogoo II
Oogoo II is basically Oogoo with the addition of graphite to make it conductive and a solvent (Naphtha) to make it possible to mix.

Add three parts graphite powder (by volume) to 1/4 part corn starch to one part silicone caulk. A typical first mix would be 3/4 teaspoon of graphite to 1/16 teaspoon corn starch to 1/4 teaspoon silicone caulk.

First mix the graphite and corn starch together with enough Naphtha to make a thick paste of the powders. Then add the silicone caulk and mix it very well with a Popsicle stick or stirring rod. You want to end up with a mix about the consistency of smooth peanut butter.

WARNING: Naphtha is a sickly-sweet smelling solvent that wants to dissolve your brain cells if you breathe too much of it. Make the mix outside with good ventilation or inside under a vent hood. Wear safety glasses and nitrile gloves, as it can be absorbed by the skin.

I tried at least a dozen different solvents. While other solvents can be used instead of Naphtha, it has the advantage that it evaporates extremely fast and most of the odor is gone in a few hours. Other solvents can take a day or two to dissipate and increase the set up time.

Mix in small batches and use it quickly before it starts to skin up. It will typically set up enough in two or three hours to de-mold. Let it completely set up overnight before using it.

Other Mixes
At about two parts graphite to one silicone caulk, the mix starts to become usefully conductive. Adding more than 3 parts graphite will reduce the flexibility of the final rubber.

Step 4Turn A Pencil Or Pen Into A Stylus

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Any pen or pencil can be made into a stylus while still maintaining the ability to write on paper.

Make A Stylus Tip Mold
A quick mold can be made by drilling a 3/8" hole in a block of paraffin or candle wax. Drill it 1/2" to 5/8" deep.

Cast With Oogoo II
1-Set up a clamp with a spacer to hold a pencil or pen 1/8" to 3/16" from the bottom of the hole and then remove the assembly from the hole.

2-Fill the hole flush with with a mix of Oogoo II.

3-Reinsert the pen or pencil and center in the hole. See thumb pic 1. With a toothpick smooth any Oogoo II that oozes out onto the body of the writing instrument.

4-After two or three hours remove it from the mold.

5-The diameter of the cast rubber tip will be larger than most pens and pencils. Mix up another batch and smooth it around the tip to taper it to the body of the pencil or pen. This will give you a conductive area to grip. You can coat the conductive rubber as far up the pen or pencil to where you are likely to hold it.

6-Let it dry overnight before you try to use it. A standard drill bit will leave a pointy tip. Sand it down lightly to make the tip more rounded.

Second thumb pic shows the finished pencil.
Third thumb pic shows a pen done in the same manner.

Step 5Make A Transparent Round Tip Stylus

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This style of stylus allows you to see with more precision exactly where you are drawing a line or pushing a button.

1-Cut a 1/8" diameter metal tube or rod about 4" long to make a handle.

2-Cut a piece of VeilSheild conductive fabric into a 3/8" to 1/2" diameter circle.

3-Set up a clamp to hold the handle about 1/8 off the conductive fabric at a slight angle.

4-Mix up some conductive rubber and put enough on the handle end to glue it to the center of the fabric while held in the clamp. See first thumb pic.

5-Let it set up for three or four hours and it is ready to use. The second thumb pic shows the finished stylus.

If you center the handle end on the fabric it will usually draw under the handle end. If you glue it off center, you can see the line as it is drawn.

Step 6Make a Transparent Paint Brush Stylus

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This stylus is flat and thin enough to put in a wallet. It draws and paints very much like a paint brush. It is pulled in the same direction you would pull a brush.

1-Cut a piece of 1/32" double sided copper clad circuit board to make the handle. Cut it 3 or 4 inches long and about 3/8" wide.

2-Cut a piece of VeilSheild conductive fabric about 7/8" long by 5/8" wide. Cut it in the angular shape shown.

3.Mix a very small amount of Oogoo II and use it to glue the conductive fabric to the end of the handle. The stylus is used glue side down so the bulge of the conductive rubber keeps the circuit board from scratching your screen.

The second thumb pic shows the glue joint.
The third thumb pic shows the top of the stylus

Step 7Other Possibilites

The step 7 pic shows how Oogoo II can be formed into thicker objects or rolled into thin sheets. It also sticks well to regular non- conducting Oogoo (the blue part of the pyramid).

Other Kinds Of stylus
There are many other kinds of shapes or forms that can be made into a capacitive stylus. An Oogoo II tipped ring might be worth a try. Other shapes of conductive fabric might produce interesting results.

Robot Skin
As the step 7 pic shows, you can form thin skins of conductive rubber that could be used to create pressure sensitive robot skin.

This kind of conductive rubber sticks well to almost anything. It also shrinks as it sets up. So if you use it to coat wires or enclosures it will shrink wrap the object. Embed an exposed wire that goes to ground and it can be used as electrical shielding.

Conductive Glue
Oogoo II works quite well as a conductive glue. A mix of 4 or 5 graphite to 1 silicone caulk has fairly low resistance and can be used to glue wires, conductive fabric, conductive thread and electronic components together into circuits.

For other ways of making conductive glue see here:

For other uses of conductive glue see here:

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