More nice materials to test!
I got these materials at the end of the summercamp:
The width is indicated in red numbers.
The samples are from Elasta: http://www.elasta.be/ . The yarns are from Soieries Elite.
The conductive grey thread is :
Elistat Pht 91 – STHT 74/3 with 75 % PES – 25 % Resistat.
It is not 100 % carbon, but a PA kernel, with a carbon surrounding
The materials are a combination of conductive (grey) and non conductive (black) material.
The grey is woven into the samples using a zig-zag in the first three samples making it stretch (elastic), the last two samples are not stretch. The stretch looks and feels wonderful!
What could be done in e-textile is use the first sample as a sensor of “how many buttons” are closed, using a conductive button.
The second with the buttonholes does not provide this possibility because the conductive wire is away from the buttonholes. But this distance gives other possibilities, e.g. testing the size of (conductive) buttons!
The three others can be very well used as touch (closing) switches, using the fact that you can scan for a contact.
The stretch one without the buttonholes could even be used as a stretch sensor, although it is not a regular stretch sensor which is made to have a range which is as linear as possible. (The measured resistance of the 4 wires parallel is between 700K and 1000K when stretched, but this seems to vary, just like knitted samples (Brother knitting machine) have an impredictable behavior, probably caused by the wires touching differently every time you stretch….)
Big resistance wire!
But there is one drawback: the conductive wire used has a very high resistance. It means you cannot use it for “heating” thermo chromic materials (you need something like 10 Ohm total for that). But you can use the voltage drop.
The resistance between two buttonholes is 900 kOhm, so already three buttonholes are outside the range of my multimeter:-) (cheap one!).
E.g. with a simple Darlington array of two BC457c you can measure the effect of touching the conductive wire in the sample (the resistance is comparable to the skin resistance). The Darlington array is sensitve enough, but also statical electricity influences the output considerably…this Darlington setup is not very good for clothing!
This post provided a simple solution for the big resistance in combination with the analog PIN of an Arduino: http://www.chris3000.com/archive/galvanic-skin-response/
The resistance of the wire is comparable to the skin resistance, so all posts on measuring the skin resistance can be used for ideas!
Just use a pull-down resistor or 500K or something, then the crocodile clamp on different buttonholes gives different values. (The metaphor is a scale: if the resistance of the sample is big, you should balance it with a big resistor.)
Using the serial window:
220 – for the first buttonhole (this provides a value for the distance between two buttonholes)
110 – for the second (distance two buttonholes etc)
80 – for the third
40 – for the last
The actual value of the numbers is not important, the difference is. This difference is quite nice, it demonstrates that you can use at least around 5 buttonholes for sensoring the number of buttons fastenend, with this distance of the buttonholes.
It means also that you can use sample 4 and 5 too for sensing where it is touched by another conductive material, giving a measure for the length.
But a lower resistance conductive thread would also give possibilities. Then you can make bigger distances more clearly measurable.
Another solution could be to make the conductive zone bigger (thread in parallel reduces resistance), although you would need a lot of these conductive threads in parallel to make the value of the resistance in the neighborhood of 5-50 Ohm useful for heating pads, this is not possible with this type of conductive wire.
(see for example http://etextile-summercamp.org/?p=540, for a tutorial on heating pads.)
Details (can be enlarged). Doesn’t this look super nice?