How a quartz watch works - its heart beats 32,768 times a second

this video is sponsored by Nord VPN in the world of watch enthusiasts there can be a bit of snobbery that says mechanical watches are far superior to battery-powered watches and I can understand why like you've got these objects that are really intricate really precise really small and yet entirely mechanical that's amazing like that's a really desirable object but when you find out how the mechanism inside a battery-powered quartz watch works it becomes equally desirable at least it did for me and it's probably the next watch that I'll get once my pebble kicks the bucket but anyway this video is about the amazing mechanism that powers a quartz watch if you want to make any kind of timekeeping device then the first thing you need is some kind of thing that oscillates where you know how long each oscillation takes so a good example is a grandfather clock so you have a pendulum where it is known that a single pendulum swing takes one second you know the period of oscillation and you can use it to drive the mechanism of the clock but if you tried to wear a pension clock on your wrist it wouldn't work because the movement of your hand would cause the pendulum to go all over the place you have the same problem if you put a grandfather clock on a actually it was the need to be able to tell the time at C that drove the development of non pendulum based clocks that ultimately led to mechanical wristwatches in a conical clock the pendulum is replaced with an oscillating mass on a spring a bit like this except that this arrangement isn't much better than the pendulum it still relies on gravity and it's going to swing around on a ship so instead you use a coiled spring and a rotating mass the rotating mass repeatedly winds up and unwinds the coiled spring like this that balance wheel mechanism is the basis of most mechanical watches and it could be incredibly accurate a high-end mechanical might only lose as many as five seconds per day and yet a battery-powered watch can easily be way more accurate than that and they can achieve that feat with a tiny tuning fork so grandfather clock uses a pendulum with a known period of oscillation and mechanical what she uses a mass on a spring with a known period of oscillation and a battery-powered watch uses a tuning fork with a known period of oscillation this particular tuning fork oscillates 440 times per second which is an audible frequency otherwise known as a above middle C it is you may already have spotted a problem with using a tuning fork to keep time which is that well you whack it to get it to vibrate but then the vibration slowly dies down until it's not vibrating anymore so how do you keep it vibrating and also how do you turn that vibration into the ticking of a clock actually both of those problems can be solved with an electromagnet consider this simplified tuning fork I don't know if you can call it tuning for it I mean it's a metal ruler and a vise but anyway like a tuning fork if you whack it it will vibrate at its natural resonating frequency unlike a tuning foot you can't hear it because the frequencies too low but like a tuning fork if you leave it for long enough eventually the vibrations will die down to nothing eventually beldam Isabella but now look at this setup I've got an electromagnet here these are the wires going into the electromagnet this one's connected to a nine volt power supply but this one's just not connected to anything so the circuits broken the electromagnet has no power but the other end of the power supply goes into the ruler so if I were to touch this wire against the ruler the circuit would be complete and the electromagnet would turn on I've also attached a permanent magnet to the ruler that is repelled by the electromagnet when it's turned on so what you can do is you can place the wire just next to the ruler so that when the ruler gets too close to the electromagnet it completes the circuit and is repelled from the electromagnet it's a bit like pushing someone on a swing every time they get too close to you you push them away you're not changing the resonating frequency of the person on the swing you're just keeping it going miss you better do that here as a bonus the current in this circuit that keeps turning on and off at regular intervals can also be used to regulate the ticking of the clock a more sophisticated and miniaturized version of this setup can actually be found in watches manufactured between about 1940 and 1960 the Accutron had a tuning fork inside that would vibrate 360 times per second so if you put the watch against your ear you would hear this sound which is nice the real revolution came with the discovery of piezo electricity I explained the piezoelectric effect in my last video and wider rises in certain crystals the quick summary here if you take a crystal of quartz and you cut it in just the right way and then deform the crystal by like hitting it for example then your measure of voltage across the crystal and conversely if you apply a voltage across the crystal and the crystal will deform so if you look inside a digital watch or an analog watch this battery-powered or the back of a battery-powered war clock you will find this component and if you take off the protective outer case there it is a crystal of quartz of course in the shape of a tuning fork if I flick this crystal it will sing like a tuning fork except that you won't be able to hear it because the frequency is too high for our ears but because it's piezoelectric it doesn't just produce this inaudible sound it also produces a detectable oscillating voltage this is a USB oscilloscope so what you're seeing here is the voltage detected across the probes and I've connected the quartz tuning fork to the probes so the moment there's nothing going on but look if I flick it I see that wave pen so that's the voltage across the probes going up and down because the piezoelectric crystal is flexing back and forth so the voltage it produces is going up and down we could take a screenshot and then try and work out what the frequency is or we can switch to frequency view where the scope is actually going to show us the frequencies so now if I flick it see that spike that appears just put a little dash line @ 32.7 kilohertz and look when I flick it that's exactly where the spike appears just like a tuning fork the vibration is short-lived and you need to find a way to keep it going like we did with the electromagnet but with a piezoelectric tuning fork you can do something really clever you take the voltage coming off the tuning fork that oscillating voltage you run it through an amplifier and then you feed it back into the tuning fork and that's how you keep the tuning fork vibrating at its own natural resonating frequency here's the quartz crystal back and sit you in that feedback amplification circuit and look here's that permanent spike now @ 32.7 kilohertz that measurement of 32.7 kilohertz is only accurate to one decimal place and I happen to know that the actual real value is 32 point seven six eight kilohertz or in other words 32,768 Hertz the quartz crystals are calibrated in the factory to be that exact frequency so they add gold to the tips of the tuning fork and then just slowly shave little bits off until the frequency is exactly right well if you know your powers of two then you might have spotted that it's 2 to the power 15 but why is it that exact number there's actually a clever reason for it but it's two really clever reasons the first is it needs to be above 20,000 Hertz because that's about the limit of what people can hear and you don't want an audible whine coming from your watch so let's make it above 20,000 Hertz and two to the power 15 is the first power of two that's above 20,000 but why does it need to be a power of two this is where it gets really clever because you can take an oscillating signal like that and you can pass it through chain of flip-flops and it will turn that 32,768 hurt signal into a 1 Hertz signal one blip per second and you can use that one blip per second to tick the second hand of your clock and when I say chain of flip-flops what I mean well a flip-flop is just a little bit of logic circuitry I'm not going to go into how a flip-flop can be built out of and gates and or gates and things like that but just know that a flip-flop can hold a state so you give it a signal and it turns on and it will stay on until you send it another signal and then it will turn off and it will stay off until you send it another signal so let's see what happens when we chained fifteen of these flip-flops together let's just look at the first flip-flop in a chain to begin with so remember you've got this signal coming in from the quartz tuning fork and that's an assign wave but this is a digital device it's a it's a smart flip-flop if you like so this is expecting just on and off there'll be some processing that takes that sine wave from the quartz crystal and turns it into a square wave like that so you've either got on or off coming into this flip-flop and the logic inside the flip-flop is arranged so that any signal that's coming in in the on position the flip-flop will flip as soon as the on signal turns off right so it's in the in the drop of the on signal right so here's the signal coming in and as it drops that's when it flips like that okay and then the the next signal comes in and just as that signal cuts off it flips again right and then the the third signal comes in and it flips the fourth signal comes in and it flips right so that's the off position that's the on position of the flip-flop and you'll notice that the flip-flop flips into the on position every second signal coming in so like all the odd signals come flipped to the on position so if you look at the frequency at which this flip-flop turns on it's half the frequency of the incoming signal and here's the cover bit you take the signal of this flip-flop and you feed it into the next flip-flop in the chain right so this flip-flop flips on and remember we've arranged the logic inside this flip-flop so it will flip or flop when the signal coming into it turns off at the moment it turns off so at the moment that this turns off this one turns on like that right then this one turns on again and then at the moment that it turns off this one turns off right and just considering these two on their own you'll notice that this one flips half as often as this one and this one turns on off half as often as the signal coming in right and then you chain this one into this one so you've got on/off on/off and but then this one turns on when this one turns off right and so the whole thing happens again on off on oh and then this one turns off at the same time with the off signal from this one the important thing is the frequency of flips and flops goes down by a half each time you progressive onto the next flip-flop and so think about that you've got a signal coming in which is 32,768 Hertz coming in this is on and off half as often as that half of that is 16,000 386 that 84 so there's no reason I'm looking over there by the way this one is half as often again which is 8192 ons per second if you like this is half of that which is 4096 and and so on down the chain these are powers of two so you've got a signal coming in with a frequency of 2 to the power 15 then this has a frequency of 2 to the power of 14 this has a frequency of 2 to the power of 13 to the power 12 2 to the power 11 10 9 8 7 6 5 4 3 2 1 this is 2 to the power 1 that's the frequency of that dude's got 1 is 2 as a frequency of two flip-flops per second so this is 2 to the power 0 or 1 so this flips every second I've actually got a redundant flip-flop here you don't need 15 you need 14 that was my mistake that's called a an off by one error happens a lot in programming so you use the signal from this flip-flop to power what's called a stepper motor which is a motor that can turn by an exact amount every time it receives a voltage so you can use that with a series of gears to move the second hand of your clock and then some other gears to move the minute hand and the hour hand as well and of course because you're dealing with an electronic signal to begin with you can avoid the mechanical world completely and just use that signal to drive an LCD display and that's how a quartz watch works any halfway decent quartz watch is only going to lose about a second a day at the most which is way more accurate than even a really high-end mechanical watch but of course a quartz watch isn't the most accurate way to keep time the most accurate way we have now is with an atomic clock but did you know this an atomic clock still uses the vibration of a quartz crystal to keep time it's just that it also uses atoms of cesium to tweak the vibrations of the quartz crystal if it seems to be drifting off so yeah even an atomic clock uses a quartz crystal I'm not gonna explain how an atomic clock works now because there are plenty of videos out there explaining that the best video explanation that I found is on the everything channel so I recommend you hop over there and watch that I'll put a link in the N screen and in the description but I also recommend you subscribe to that channel because lately he's been making these like cinematic epic videos where you also learn about science really amazing so head over there what's the video about atomic clocks but also subscribe this whole video came about because I was looking at how computers know what time it is and how they synchronize around the globe using network time protocol because I was doing a security audit and it turns out having an accurate time when your devices is important for security who knew I was also looking at VPNs as well so I decided to reach out to Nord VPN to see if they sponsor this video because that's the view pin that I use now and so yeah they're sponsoring this video you know this VPN stands for virtual private network but what it really means is that all your online activity is secure it's anonymous your IP address is hidden everything's encrypted you know look you've got nothing to hide right but all that data that's spreading out of your device is valuable and it can be used in ways which is not necessarily good for the user as a bonus by the way if you ever get this message on YouTube that says this video can't be viewed in your country with a VPN you can make your computer appear to be in a different country and it's really easy to do through Nord VPN it's one of the things I like you can get it on your computer but it's also for Android and iOS devices if you go to North Vee PN comm forward slash Steve now you'll get 75% off which is just two dollars 99 and if you use the promo code Steve when you check out you'll get the first 30 days absolutely free so check out Nord VPN today I hope you've enjoyed this video if you did don't forget to hit subscribe and I'll see you next time [Music]

Channel: Steve Mould

Views: 3,259,670

Rating: 4.9245129 out of 5

Keywords: clock, timekeeping, explained, understand, resonator, timer

Id: _2By2ane2I4

Length: 17min 35sec (1055 seconds)

Published: Thu May 23 2019