How to Make a Soft-Potentiometer

Electronics is always fun when you try to intervene it with something of your interest, like crafting. How about sewing circuits on cloth instead of connecting them on breadboard? This instructable is about how to make a 'wire-free' simple soft-potentiometer and use it to vary the brightness of LEDs. This product also shows how soft circuits can be used to explain electronics in a much more crafty and fun way.

1) Cloth (around thrice your desired bag size)
2) Fabric paints
3) LEDs(colors of your choice)
4) 3V coin cell battery
5) Conductive thread(Silver plated nylon conductive thread and a low resistive conductive thread)
6) Normal thread and needle
7) Elastic battery holder(or any coin cell battery holder)
8) Tiny pieces of conductive fabric
9) Transparent cello tape
10) A bead (or something similar)
11) Scissors
12) Round nose plier

This bag is of size 12x14cm. I took a cloth piece of double this length (but same breadth) so that if I just fold this piece once I will get my bag’s size. Dividing this piece into half, on one side I painted the picture (of Pooh and Piglet) in which I wanted to keep LEDs at the shown places. After the paint dried, I sewed the pattern over the snail with high resistive conductive thread (silver plated nylon thread). This forms the variable resistance part.

I painted some stars on the second side of the cloth. This forms the backside of the bag.

On another piece of cloth, apparently the size of the bag, mark the exact points where the LEDs should be and also the variable resistor part’s end. Draw the circuit on the cloth.
‘+’ and ‘–‘ corresponds to positive and negative from the battery (will be shown in the coming steps).

Insert LEDs into their positions and curl up their legs using a round nose plier. Positive of the LEDs should be poked in through the mark along the line from positive of the battery.

This is an optional step. Instead, you can use any 3V coin cell battery holder.
To make this elastic battery holder:- Take a piece of elastic just enough to wrap the coin cell battery. Mark the points where the center of the battery on both sides touches the elastic. These will form the two terminals (+ and-). Stitch a small piece of conductive fabric using conductive thread to these terminals (inside the elastic battery holder). Conductive fabric is used just to ensure better connection.

Now connect the elastic battery holder. Stitch it in the middle of the top edge so that it will be easier to insert and remove the battery.  Mark positive (+) and negative (-) on the elastic battery holder so that you know how to insert the battery. Sew the connections as per the diagram using less resistive conducting thread(dark brown colored one).

Don’t forget to leave a length of thread, dangling and wounded around a bead, from the negative of the second LED(here, the yellow one).The length of the hanging bead should be such that it can touch both ends of the variable resistance part.

Since the variable resistance part is in the upper layer, sewing a small piece of conductive fabric to the end portion will strengthen the connection between the layers.

Fold inwards the painted cloth and stitch 2 of the adjacent edges so that now only top edge is left open. Make holes in the first layer for the LEDs. Insert them through these holes and also the bead along with its connection.
Now the cloth with circuit stitched on it is upside down on the inside of the bag. To keep the cloth in place, I used transparent cello tape over all the 4 sides and also stitched the four corners with the first layer. This should hold it in place.

Now turn the bag inside-out and insert a battery in the battery holder according to the polarity that has been marked on it. That is it!!!!!!!!! Now both the LEDs glow very bright when the conductive thread wound on the bead is touched to the thinner end of the varying resistance part. This glow should dim as the bead is moved from the thinner end to thicker end. This is because, this silver plated nylon conductive thread has a high resistance, and as the bead is moved, the resistance included in the circuit changes hence the brightness too changes.

I was a student intern at Ammachi labs when I was introduced to soft circuits. I wanted to start with a soft circuit which was simple but could be helpful in showing some basic electronic principles.

We have not included any resistor because; the conductive wire itself provides a resistance per unit length. This is enough to protect the LEDs.

You can see that for the same voltage, different colored LEDs glow with different brightness.
This model can also be just filled in with some cloth or cotton to get a cushion with an electronic circuit on it.