I published another tutorial about how the people from Softlab here in Umea adapted a sewing machine to use conductive thread. This tutorial will show how to create a pressure sensor using that machine. I also used other machines that are available here.
Of course, in case you do not have those equipments around you can adapt and do it by hand. The important is to make it work!
This is what you will need:
- the adapted sewing machine
- 2 pieces of fabric. I used cotton. Bare in mind that the sensor works better if the fabric is not elastic.
- conductive thread.
- a piece of foam 2mm
Step 1: Drawing the Shape of Your Sensor
- Place the 2 pieces of fabric on top of each other. I like to pin them to be sure that they will not move during the manipulation.
- Draw on the fabric a square of 10cm. You can use a fabric marker or actually anything that leaves a trace.
This will be the size of your sensor. If you want a sensor with a different form factor just draw it in a different way.
Step 2: Sewing the Conductive Thread
Use the sewing machine to sew the tread inside the 10cm square. You can use any type of stitch. The important this is that the conductive thread on the bottom cover as maximum of area as possible.
Step 3: Cutting Out the Squares
Another super cool machine they have it here at SOFTLAB is the Overlock Machine. It is used to finish the edges and here we will use it to cut the square and prevent the fabric to unravel. You can find more information about overlocks machines here.
Step 4: Cuting the Foam
Now that we have the fabric with a conductive thread in one side and a normal thread on the other side we need to create something in between that will prevent the conductive thread to touch each other all the time. What we want is to create a switch and to do that we will place a piece of foam with holes in between the fabrics.
The idea is that when there is no pressure the foam keep the fabrics with conductive thread separated and therefore there is no connection. As soon there is pressure, the fabrics with conductive thread will touch each other, activating the button.
To cut the foam I used another machine available here. A laser cut machine. On the picture you find the settings I used to cut the 2mm foam. You also find it here the file with the cuts.
At the end you will have 2 pieces of fabric with conductive thread and one piece of foam with holes.
Step 5: Putting the Pieces Together and Test
Now what you need is to make the "sandwich" with:
Fabric with conductive thread facing down
Foam with holes
Fabric with conductive thread facing up
I liked to pin the together and test with a multimeter. if everything goes right you can use a sewing machine to fix all together. Here I used a super fancy Juki one. But of course you can use any sewing machine or even do it by hand. No excuses....
after you sew it you can attach the rest of the conductive thread to a metal snap or just leave like that and use a crocodile clip to attach it to your circuit.
I hope you had fun.
You find more information about Sliperiet and the softlab in this link: http://sliperiet.umu.se/sv/