Assignment | 24 oktober 2017

Produce one soft sensor by experimenting with the materials available at the lab.

ref.: http://fabricademy.fabcloud.io/handbook/classes/04_etextiles.html

( inspiration - project examples : http://www.kobakant.at/DIY/?p=4855 & Fab Academy project presentation.html )

Since copper sticker does not stick well directly to fabric I was curious if this could be kept in place by adding a layer of heat pressed vinyl (poly-flex 401) on top. Another layer was added to the bottom to prevent the circuit touching the skin trough the fabric.

Design consist of 2 experiments, 1 straight connection and 1 crossing connection to see if multi layer circuits are an option.

Conclusion is that a multi layer circuit is possible. The vinyl between the copper pieces is a good insulator.

(1.3 ohm measured is the resistance of the leads as shown in the first picture).

Here I'm using 2 small magnets on the outside of the fabric to hold 2 patches of copper together to complete the circuit.

Soldering in combination with heat pressed vinyl posed no problem. I was afraid that the vinyl would melt and retread from the heat of the soldering iron, but it performed excellent. Even deliberately working on the edge is fine. The tin wants flow on copper not the vinyl.

I realized that a coin cell battery is magnetic. So placing the battery in between 2 copper pads and holding it in place with magnets on the outside of the fabric works too.

I knew the heat pressed vinyl has no problem surviving the laundry, but I was curious if the copper would be ok too. So I've let the test pieces sit in detergent overnight. One bowl in boiled water and one in hot tap water, both with 5 grams of mild powder detergent. I'm testing this because in Iceland there is sulphur in the hot tap water. And the pieces came out looking just fine.

Even when wet, the vinyl is a good isolator. Because the top vinyl layer and the bottom layer merge together when pressed they form a good seal. But do realize that either the fabric or/and the thin layer of water are still conductive. So to completely waterproof the circuit also all the contact points need to be sealed in / protected in some way.

connectivity when everything is wet :

connectivity with one drop of water on top of vinyl:

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