Tag Archives: electricity

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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Circuit boards

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.

This will look better when I paint it. For one thing, the board will be a lovely green. The bigger, more complicated circuit boards look like city maps.

If you’ve ever wired something—like a lamp—you’ll remember getting out the needle-nose pliers and wire-cutters, maybe a razor blade to strip the insulation off the wire ends; you wrap the exposed copper wire around the appropriate screws then tighten ‘em up so the wire stays put…I’m trying to imagine how you would wire something as minuscule as the insides of a watch. Wires would need to go from the battery to the quartz crystal, back to the battery with a detour to power the hour, minute & second hands after counting how many oscillations the crystal made.

The circuit board is a flat card made of plastic or resin. Instead of wires, circuitry is printed right onto the card in metal ink. A circuit board can get a complicated electric network crammed onto a very small area. A small circuit board in a watch can direct electric power from a battery to the quartz crystal and anything else inside the watch .

You can see the circuit board at 27:20 https://www.youtube.com/watch?v=SFiq8WDx5Is

The History of Circuit Boards


https://www.pcb-solutions.com/pcb-market-monitor/the-history-of-pcb-infographic/
Those old discarded mass-produced watches and circuit boards can become playthings for someone with electrical knowledge—http://www.angelfire.com/ut/horology/quartz.html
https://sound-au.com/clocks/timebase.html

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Quartz crystal

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.

Quartz is a common mineral that does this weird thing: it generates a tiny bit of electricity if it’s squeezed, and vibrates when you send an electric charge through it. Watchmakers cut quartz into a shape that looks like a tuning fork, so it vibrates like a tuning fork.

So if we just squeeze the quartz—I’m not sure if this is really the way it happens…

…wow! It works! (photo credit: KTUL.com)

Amazing!! (photo credit: Google Earth)

Okay, okay, that was just a gag. You knew that, right? Just a teeny tiny electrical charge passes through the quartz crystal to regulate the watch.

“Inside a quartz clock or watch, the battery sends electricity to the quartz crystal through an electronic circuit. The quartz crystal oscillates (vibrates back and forth) at a precise frequency: exactly 32,768 times each second. The circuit counts the number of vibrations and uses them to generate regular electric pulses, one per second. These pulses can either power an LCD display (showing the time numerically) or they can drive a small electric motor (a tiny stepping motor, in fact), turning gear wheels that spin the clock’s second, minute, and hour hands.” https://www.explainthatstuff.com/quartzclockwatch.html

https://electronics.howstuffworks.com/gadgets/clocks-watches/digital-clock2.html

A Short History of Digital Clocks and Watches

https://h2g2.com/edited_entry/A1006534

A Brief History of the Wristwatch – Part 1

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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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