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Update: the circuit has been revised, filler-liquid replaced, circuit board is assembled, software ready

My website and my projects are non-commercial, they are nothing more than one of my hobbies and my intention is to motivate other people to deal with this interesting subject.


As a German native speaker, I tend to make some mistakes. If you find them, you can keep them, I don't need them anymore.

I have only rudimentary knowledge in chemistry and physics and I have never been involved with elecrowetting.

I am no scientist, so please have no scientific expectations on this content.


Why a watch?

Well, a couple of years ago I built my laser machine (Details under “Laser”). When it was finished, I had a solution without a problem for it. So I decided to build a watch with moving droplets. My first approach was a dot-matrix display. A demonstration video can be seen here  (and I will continue with this in the future). Then the problems started: I had to deal with electrolysis, trapped charges in the dielectric, degradation of the hydrophobic coating... as soon as a problem was solved, two or more new arose. Finally I succeeded in moving some droplets forth and back for ~100000 cycles. It was time, to complete an application because my maltreated soul needed some success. As the control of a dot-matrix display is much more complicated, I decided to build a quasi-analog display. When you look at the video above, you can see, that it is not perfect. There is one point, where a droplet is a little bit sticking. I inadvertently had touched the Fluoropel coating and damaged it but I didn't want to scrap the display. In the watch the droplets will move differently than in the video, where the electric field is never turned off completely. There will be given a time for contraction of the droplets.


Watches can be gorgeously irrational. You can buy a watch for a few Euros and it will show the time and you can buy a watch for several thousand Euros and it will show the time – if you don't put emphasize on accuracy. It's like riding a motorbike, not the destination, but the journey is the reward. Boys' toys!


What is the Dropletwatch?


The Dropletwatch uses three tiny droplets of a polar liquid (ink) instead of hands. They are driven in three concentric circles by a phenomenon called electrowetting.

Electrowetting modulates the contact angle between the polar liquid and the hydrophobic/superhydrophobic resting surface by means of an electric field.

A droplet always overlaps three adjacent electrodes. Since a part of the droplet is on a not energized (grounded) electrode and the other part is on an energized electrode, the droplets meniscus is deformed asymmetrically, which results in a driving force towards the energized electrode.


What are the advantages of this kind of display in general?


It's bistable, only during movement power is drawn, it doesn't need refreshing as LCDs do.

It's ideal in very bright ambient light with excellent contrast ratio.


What are the advantages of my display in particular?


I found a way to produce a colored (bright white) reliable dielectric with good dielectric properties. (Details in section “Display”). This greatly improves the contrast, because the droplets are placed directly on the reflective surface. Usually the reflective coating is on the back of the ITO coated glass, which means, the light first has to pass the dielectric and ITO coated glass to reach the reflective coating, and then a second time the same path on its way thrown back by the reflective coating until it reaches the droplets. A further consequence are shadows of the droplets on the reflective coating because of this distance.

My design inhibits shadows and enhances the brightness. Its comparable to (red) ink on white paper.


I could greatly reduce the actuation voltage and reliability by finding a way of selectively coating parts of the droplet's moving path superhydrophobic. (Details in section “Display”). This helped reducing the friction and preventing voids of the hydrophobic Fluoropel coating on some parts because the topography makes them unsuitable for spin coating.

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