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

Step 2 Glue LEDs And Sew A Circuit

The double sided circuit in pic5 is an 3 X 5 alphanumeric LED display that is controlled by a 18x Picaxe micro controller. It can display letters and numbers in preprogrammed sequences that are selected by adjusting the wiper magnet on a flexible potentiometer. The voltage from the potentiometer is measured by an ADC (analogue to digital converter) input of the micro controller to select the different sequences.

You can download a video file that shows the circuit flashing a message at: http://www.inklesspress.com/rollup-circuit.wmv

Materials

Fabric of your choice

Conductive Glue (see previous step)

LEDs available from Electronic Goldmine- http://www.goldmine-elec-products.com/

Conductive thread-Available in small spools at: http://members.shaw.ca/ubik/thread/order.html
Or at: http://www.sparkfun.com/commerce/categories.php?cPath=2_135

1- Choose a fabric-You can glue onto just about any fabric. I have glued onto cotton, nylon, polyester, neoprene, and Dacron. For this project I chose a white polyester fabric used for shower curtains because it tends to lay flat when rolled open. I cut the fabric using a hot knife so that the edges would not unravel. The hot knife was just a 20 watt soldering iron with the tip filed to a knife edge. The hot knife was also handy to melt between glued pins or pads that became shorted from glue overflow.

2- Punch holes for components. If you are using a loose weave fabric your led leads may poke right through. With synthetics like polyester or nylon, you may have to heat up a small wire with a torch to melt holes for your led and IC leads.

3- Tie conductive thread to each led lead wire. I prefer a double overhand knot pulled tight. If you can, it is best to bend and crimp the wire over the thread so it cannot pull lose. This will also lower the resistance of the joint.

Then use mix #1 to glue the thread to the led lead. You can also use paint mix #2, but you will have to do two coats and it has a tendency to flow more than you might like because of capillary action. Try and make sure each connection is coated all the way around. This will seal out most air and moisture and guarantee more than just a mechanical electrical connection to the thread. If you just sew the thread around the component leads without the glue, electrolysis and oxidation of the connection can occur over time. The connections of just a sewn circuit can also loosen over time.

You can also use paint mix #2 to make connections as it tends to flow better around the joint and sticks better to the fabric. The only problem is its higher resistance and its tendency to shrink very thin. This often makes it necessary to do two coats on a joint.

Be very careful when gluing the black bodies of integrated circuits as it is very easy to get a thin and almost invisible coating of the black conductive glue in between the pins. This can short out the pins. Every time I have glued in an IC I have shorted out several of the pins. While this did not damage the IC, I had to spend quite a bit of time with a high power magnifier scraping off the offending glue before the circuit would work.

You can then hand sew the thread to run on either side of the circuit to the appropriate components.

If you do not want to bother with glue and you are good at sewing, Laura Beauchly has worked out a whole system to sew all kinds of components onto fabric. She has also done some interesting things using laser cut conductive fabrics to make flexible circuits. Details available at: http://www.cs.colorado.edu/~buechley/

She even has designed some sew able components available at: http://www.sparkfun.com/commerce/categories.php?cPath=2_135