Conductive Glue And Conductive Thread: Make an LED Display and Fabric Circuit That Rolls Up.

Step 3 Make Magnetic Glue, a Flexible Potentiometer, and a Plug and Socket

Magnetic Glue
To make a flexible potentiometer or a magnetic plug and socket or a magnetic power switch, we need a glue or paint that will attract magnets. Magnetic paint is available commercially and is somewhat expensive. Obviously the paint is not actually magnetic, it is only a paint with a powdered metal filler, usually iron, that attracts magnets. This glue is similar.

You can mix up your own ferromagnetic glue using iron powder available at: http://www.elementalscientific.net/ Or you can take a strong magnet, put it inside a plastic bag and run it through some dirt or sand at the beach or in an arroyo. It will pick up black iron ore also known as magnetite. Use the magnet in a bag to refine the mineral particles until they are mostly the small black particles with the lighter dirt or sand removed. These particles are ferrimagnetic, which means they will attract a magnet but will not tend to become magnetized.

Mix #6 Ferromagnetic or ferrimagnetic glue
Mix the magnetic glue 1-1/2 iron powder or iron ore to 1 DAP contact cement by volume.

Make a flexible potentiometer
Use the techniques described in step 6 to make conductive fabric using Mix #7 Resistor glue. After it dries, you can then cut it using scissors into a long strip about 1/4" wide by 3" long (pic 7c). You can then coat the back with a thickness of about 1/32" to 1/16" of Ferromagnetic glue. This gave me a potentiometer with a resistance that varies from about 30K to 200 ohms. It was later glued with contact cement onto the fabric circuit.

Mix #7 Resistor glue
Mix the resistor glue 1/2 Graphite to 1 Dap contact cement by volume

The wiper contact (see pic 7a) is a neodymium magnet that is first tied with conductive thread and then coated (see pic 7b) with conductive glue mix #1. The conductive wiper, attracted by the ferromagnetic glue on the back, can then be slid along the length of the flexible resistor, to vary the resistance.

Make a Magnetic Plug and Socket
For the socket (see pic 9a), sew conductive thread in a loop for each contact and then cover it with mix #4. Place something flat and non-sticky such as silicon caulk coated glass on top of the contacts as they dry to create a flat surface. After they have dried, coat the back side with mix #6, ferromagnetic glue.

For the plug, a ring magnet works well. Most neodymium magnets are metal plated to protect them from deterioration, so they are electrically conductive. If you are making a plug with several contacts you will first have to coat the magnet with a non conductive glue such as DAP or Welder or Goop contact cement. After it dries, you can then wrap wires (pic 8) where you want the contacts and coat each one with conductive mix #4. Place it on a non stick flat surface such as silicon caulk coated glass or wax paper to flatten the contacts as they dry. Pic 9b shows the completed magnetic plug and socket. On the one I made, the resistance of the contacts between the plug and the socket was 80-100 ohms. Certainly low enough for signal transfers.

Make a Magnetic Power Switch
Pic 9B shows a simple switch using a plated neodymium magnet. First sew two separate contacts using doubled conductive thread. Then coat the back with magnetic glue leaving enough room above the contacts to dock the wiper magnet. To turn it on you simply slide the magnet over the two thread contacts. The one I made had an on resistance of about 1.16 ohms with a 3/16" x 3/8" magnet. With a thinner 1/16" x 1/4" magnet it had a resistance of about 1.63 ohms when on.

The resistance is even lower if 24 gauge, tinned solid copper wire is used as the contacts. I got a resistance of .02 ohms with wire.

With more contacts around the magnet dock even rotary switches can be made. Or with two magnets--DPDT switches can be made.