Tag Archives: battery

The liquid crystal display explained!

Three inventions moved clocks and watches away from being mechanical/analogue so they could become digital: The quartz crystal, the circuit board and the liquid crystal display.

Okay, I sort of explained how a battery works. I kind of explained how a quartz crystal works. The circuit board was easy—even a shmo like me can explain printed metallic ink on a plastic card. But—liquid crystal display? I started this post about 17 times and kept getting lost in the weeds with carrot juice and double melting points and twisted nematics and polarization…

Let’s start here: analogue clocks and watches were inaccurate because they have physical, mechanical moving parts. So we replaced the wound-up mainspring with a battery. We replaced the balance wheel with a vibrating quartz crystal. Now we need to replace the moving mechanical gears, hour-hand and minute-hand with a digital (just the numbers) display of the correct time. How do we do that?

A digital wristwatch made by the Japanese company Casio.

Instead of mechanical gears and hands, we’re going to use electricity and light.

We want a watch-face that will light up and show us what time it is. We want most of the face to light up except the numbers, which should be black so we can read ‘em easily. We’ll block the light in the shape of each number so it shows up black. The numbers will change every minute, so we need a way to change the blocked areas every minute.

In order to block the light, we need a filter. The filter lets us control which rays of light pass through and which rays get blocked. A filter could be a wall of liquid filled with crystals that all face the same direction. The lined-up crystals let the light pass through. We’ll sandwich this wall between 2 plates of glass. The crystals still let light pass through—until we zap them with a little electricity. The electricity upsets the crystals so they don’t line up anymore and light can’t pass through.

We’re only going to zap in certain areas. We want those certain areas to be shaped like numbers. For instance, when we zap the glass in the shape of a ‘3,’ those crystals in the 3-shape get upset and don’t line up with the rest of the crystals in the wall. Light can’t pass through the 3-shape, so we see a black ‘3’ on a lighted watch-face.

Just like on a circuit board, we’ll print the numbers onto the glass in ink. This ink is transparent—and it conducts electricity. Each number is designed as a 7-segment figure, so we can zap only the segments that form a ‘3,’ or whichever number we want. Each segment is wired to the battery.

This is the principle behind LCDs. It’s a simplification. I left out a lot of stuff. But you get the idea, right?


https://electronics.howstuffworks.com/lcd.htm
https://electronics.howstuffworks.com/gadgets/clocks-watches/difference-between-quartz-and-liquid-crystal2.htm
http://www.madehow.com/Volume-1/Liquid-Crystal-Display-LCD.html

Many thanks to a couple of the Western Civ Irregulars, Diana (Ms Physics) and engineering-wiz Don M—both pals of mine since childhood. They pointed me in the right direction when I couldn’t find a way to explain this one.

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How batteries work

A battery is a container—inside it are chemicals that react to metal or each other. Their reaction releases energy in the form of an electric current. The battery directs that current (electrons) to a negative terminal. The positive terminal on the other end of the battery absorbs the current. The electrons leave the negative terminal when it’s connected to something like a flashlight, light up the bulb, then return to the battery at the positive terminal.

https://electronics.howstuffworks.com/everyday-tech/battery1.htm
https://www.thoughtco.com/battery-timeline-1991340

https://www.explainthatstuff.com/batteries.html

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The Hamilton wristwatch

It’s the hairspring that made watches—which are just little clocks—possible. You wind up the hairspring and as it uncoils it releases energy to power the watch. Since the hairspring is small, watchmakers could miniaturize the balance wheel and gears, too.

But if you really want precise timekeeping, a watch’s design must have as few moving parts as possible. Watches were mechanical. Mechanical or analogue machines (a clock or steam engine or internal combustion engine) need constantly to be fussed with: you have to oil the gears; or correct for changes in temperature or humidity; friction slows down the machinery; you have to wind it or feed it fuel…if you could just get rid of those moving parts, you’d have a more reliable watch.

A small electric battery

The switch away from analogue didn’t happen all at once. When batteries became small enough, the first electrically-powered watch showed up in 1957. It was battery-operated, but still had mechanical moving parts, like gears and a balance wheel. It was made by the Hamilton Watch Company of Lancaster, Pennsylvania.

Inside the Hamilton wristwatch

http://www.crazywatches.pl/hamilton-titan-500-electric-1957

The wristwatch’s battery is really small

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