16th Oct 2007

The schematic diagram of the LED driver circuit is finally done, and linked up with the PCB diagram. As in this circuit, it involves a lot of surface mount components, I spent quite some time design my own library. And the difficulty with the PCB diagram is there are many lines as we are controlling 10 modules with 3 LEDs each. As LED driver we bought is surface mount with very small pins, the distance between the two pins is too small for us to use a 15mil track which will cause difficulty in fabricating PCB in school.

Previously the problem - only being able to display one color on fabric after being heated up has been tested out again. I found when the current is around 0.2A, it will heat up the material very fast to colorless; while around 0.15A will heat up the material slowly to make the blue color disappear. This means, when the current is low, the heating of the yarn is only slightly above that of the heat distribution from the yarn, and when color is higher, the heating will be much faster than distribution and hence will not be able to see the blue disappear in the whole fabric before the fabric turned colorless.

I tired with:
1. the fabric that is printed and with yarn sewed on
2.fabric that is only with yarns on top of which is the silkprinted fabric

And when current is low, from 31 to 37, the color changing is very slow, this may be because the higher the temperature, the faster the heat loss.

recommended way:
As the heat loss from 37 back to 31 is very fast, we can first let it change to final color, and through temperature control to wait it reduce to the desired temp.

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