Zebra Considerations

What happens combining energy harvesting and subversive.

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Two summercamps ago Mika brought some marvellous zebra material, stretchy and alternating conductive and non conductive stripes.

This material allows a politician to make more and more and more. Voltage in this case. Just rub the strips and the Voltage will reach the skies. A short trip to Switzerland or Panama to charge your supercap, and the process can be restarted again. Utopia when all greedy politicians have finally left to their paradize? (Don’t tell the guy that E = V*I so all his efforts are in vain…)

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The boost circuit with the aluminum stripes seemed to be perfect for it. Could the zebra function in the same way? Aluminum and zebra are different though, what works for one material is not always immediately working for the other. During the little time of prep for the prez you don’t need a problem case for research. The reason was that the zebra conducts, but still has a small resistance say 10-30 Ohm. So the circuit which worked for the aluminum, didn’t for the zebra.

Screen Shot 2016-08-20 at 18.05.16(Paula showing zebra summercamp 2014) Screen Shot 2016-08-20 at 18.07.14

After the summercamp time to do some experiments. Adding a transistor which acts as a switch moved the resistance problem out of the way, because this base should anyway have a resistor of 1-2K Ohm, 30 Ohm more doesn’t have any effect.

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The boost (going from 1.5V to 3V) works because the coil stores energy by building a magnetic field inside, when the voltage is applied. When you open the circuit, the magnetic field is still in place and releases the energy in the open line, building a high voltage point for a while. Normally dynamic properties of circuits are not very important in our simple DIY e-textile electronics. I wondered how fast the coil builds the field. The aluminum strip structure is apparently far to wide even if crossed with speed. So a few tests, one with parallel lines of thin copper wire (left) and another with lines of thicker conductive yarn wire (right).

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The wire experiment showed something slightly dangerous, also visible with the aluminum…it produced small sparks! The boost indeed gives a high voltage. Sparks and yarn or cloth … not so nice! The crossing the parallel wires also showed on the oscilloscope to have a rather chaotic result, certainly not going on and off in a regular way, apparently coming of a copper wire is a very bouncing experience.

copper_wire conductive_yarn

Another more controled experiment was made with an ATtiny, just do the blink script with a small delay and look on the oscilloscope for the jumps, fit the delay so that the signal gives “only jumps” and the effect should be maximum for the given coil. A coil with a few windings asks for more fast switching (eg 80 microseconds), while a coil with more windings can do the boost in bigger delays (1 millisecond). This visualized the dynamic building of current within a circuit after switching. This time is eqivalent with the speed a magnetic field is built up inside the coil. Left not yet optimized, right optimized.

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Connecting to the zebra fabric can be done in two ways, the first is that it acts as one surface, touching it with a wire connected to the circuit. The second way is more elegant, without any connectd wire: connect the zebra stripes skipping one stripe, then connect the next stripe skipping one stripe. Now you only have to touch two zebra stripes with a conductor, and the switch works.

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On the right picture you can see that the stripes are sewed together, so the connections visible in the left picture, don’t go all around.

The zebra works – with a silver cloth you get a signal signature like the copper conductive yarn, with a metal pin crossing the zebar stripes, you get a signal more like the copper wires:

zebra_b_silver zebra_b_metal_pin

Now look for the sparks when we use the zebra fabric to boost instead of the copper wires … do we catch fire? (It was too difficult to catch the sparks on camera.)

The usefullness of this circuit? Well, it uses the zebra as a switch for the boost, so that several LED’s can light up. We only need a 1.5V battery. But of course, a 3V coin cell plus LED’s works as well without this whole boost business. But the experiment was very interesting,  seeing the dynamic behavior of a circuit, learning about the zebra fabric and the ladders made of copper wires which are not behaving at all regularly as a microcontroller can perform. And using the 3V wouldn’t allow to relate to the nice metaphore for the guys trying to fill their own pocket with money belonging to the society.

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