1 00:00:00,080 --> 00:00:02,557 You may have noticed that every time I say 2 00:00:02,557 --> 00:00:04,533 “it’s time for a simpler video” 3 00:00:04,533 --> 00:00:05,538 it’s a lie. 4 00:00:06,122 --> 00:00:09,013 For the record, it doesn’t start as a lie 5 00:00:09,013 --> 00:00:10,000 it’s just… 6 00:00:10,578 --> 00:00:14,088 well, I start writing the script at the beginning. 7 00:00:14,088 --> 00:00:16,022 Seems to make sense to do it that way. 8 00:00:16,022 --> 00:00:17,614 And so, I’ll say 9 00:00:17,614 --> 00:00:19,133 “ah, this is a simple idea! 10 00:00:19,133 --> 00:00:20,244 It’ll be simple! 11 00:00:20,244 --> 00:00:21,249 Simple!” 12 00:00:21,375 --> 00:00:24,654 and then it just snowballs into a five part series. 13 00:00:25,040 --> 00:00:26,093 Not today! 14 00:00:26,093 --> 00:00:28,477 We are just gonna talk about this thing. 15 00:00:29,120 --> 00:00:32,560 Back when I made the humidifier  video I showed one of these.   16 00:00:32,560 --> 00:00:34,616 It’s a basic hygrometer. 17 00:00:34,616 --> 00:00:36,389 It has a dial and a pointy bit 18 00:00:36,389 --> 00:00:39,064 and what the pointing bit points to is, roughly, 19 00:00:39,064 --> 00:00:41,568 what the ambient relative humidity is. 20 00:00:41,568 --> 00:00:42,609 Simple. 21 00:00:42,609 --> 00:00:44,685 Some of you asked how this works. 22 00:00:45,280 --> 00:00:48,266 And honestly, yeah that's pretty intriguing, isn’t it? 23 00:00:48,266 --> 00:00:50,675 It doesn’t take any batteries, and if you look through the back 24 00:00:50,675 --> 00:00:54,307 you can kind of get a peek at a coil-like thing. 25 00:00:54,307 --> 00:00:57,035 That looks an awful lot like a bimetallic strip! 26 00:00:57,280 --> 00:00:59,665 What’s a bimetallic strip, you ask? 27 00:00:59,665 --> 00:01:02,104 It’s a strip made of two metals. 28 00:01:02,104 --> 00:01:06,193 That’s useful because different materials  have different thermal expansion properties. 29 00:01:06,193 --> 00:01:09,127 Virtually everything expands a bit when it gets  warmer, 30 00:01:09,127 --> 00:01:11,074 and metals are no exception. 31 00:01:11,074 --> 00:01:15,164 But how much they expand depends on the specific material. 32 00:01:15,164 --> 00:01:17,744 When you take two metals that are not the same 33 00:01:17,744 --> 00:01:20,539 and sandwich them together in the form of a strip, 34 00:01:20,539 --> 00:01:23,576 the mismatch in thermal expansion coefficients between them 35 00:01:23,576 --> 00:01:27,884 will cause the strip to bend slightly as the temperature changes. 36 00:01:28,240 --> 00:01:30,739 Bimetallic strips are in all sorts of  places, 37 00:01:30,739 --> 00:01:32,777 from the world’s greatest toaster, 38 00:01:32,777 --> 00:01:34,333 to blinking Christmas lights, 39 00:01:34,333 --> 00:01:36,395 to the thermostat of space heater, 40 00:01:36,395 --> 00:01:37,462 to, well, 41 00:01:37,462 --> 00:01:39,203 thermostats in general. 42 00:01:39,203 --> 00:01:42,435 But a classic and simple application of the bimetallic strip 43 00:01:42,435 --> 00:01:45,215 is in a thermometer like these. 44 00:01:45,215 --> 00:01:47,322 And let’s just get it out of our systems, 45 00:01:47,322 --> 00:01:50,295 yes these numbers are meaningless to many of you out there 46 00:01:50,295 --> 00:01:54,438 and maybe one day we’ll stop using this temperature scale ‘round these parts 47 00:01:54,438 --> 00:01:57,888 but I can’t think in Celsius any more than you can think in Fahrenheit 48 00:01:57,888 --> 00:02:02,850 and besides, a zero to one hundred scale that  correlates well with the range of tolerable ambient temperatures 49 00:02:02,850 --> 00:02:05,370 is a more pleasing way to do it from my perspective and - 50 00:02:05,370 --> 00:02:06,973 hold on this is a tangent, now. 51 00:02:07,455 --> 00:02:08,850 I want to show you something. 52 00:02:08,850 --> 00:02:09,764 See this? 53 00:02:09,764 --> 00:02:11,628 This is called a search engine. 54 00:02:11,628 --> 00:02:13,572 There’s all sorts of them out there these days. 55 00:02:13,572 --> 00:02:15,405 And most of them let you do this: 56 00:02:15,760 --> 00:02:17,598 70 f to c. 57 00:02:17,598 --> 00:02:18,396 Blam. 58 00:02:18,396 --> 00:02:19,267 There it is. 59 00:02:19,267 --> 00:02:20,746 You have a smartphone, right? 60 00:02:20,746 --> 00:02:24,094 It probably has a search bar in a very convenient place. 61 00:02:24,094 --> 00:02:26,223 Oh and maybe you even have a voice assistant 62 00:02:26,223 --> 00:02:31,034 you can literally just ask what whatever temperature is in whatever other scale you like better. 63 00:02:31,034 --> 00:02:33,003 It really is that easy. 64 00:02:33,600 --> 00:02:34,945 Now, when it's appropriate, 65 00:02:34,945 --> 00:02:37,895 I’ll continue to provide conversions here on this YouTube channel 66 00:02:37,895 --> 00:02:39,944 because it would be careless of me not to, 67 00:02:40,118 --> 00:02:43,893 but when I dare to offhandedly tweet something 68 00:02:43,893 --> 00:02:46,154 and use one of our silly units 69 00:02:46,154 --> 00:02:47,385 I don’t wanna hear it. 70 00:02:47,385 --> 00:02:51,006 You’ll spend way more time composing your complaint to me 71 00:02:51,006 --> 00:02:54,108 than you will just googling the conversion yourself. 72 00:02:54,108 --> 00:02:58,424 We are all very aware of how silly the aversion  to the metric system is 73 00:02:58,424 --> 00:02:59,820 but we can’t help it. 74 00:03:00,240 --> 00:03:01,691 Oh, and yes I am on Twitter. 75 00:03:01,691 --> 00:03:03,454 It’s mostly puns and other dad jokes. 76 00:03:03,454 --> 00:03:05,294 And snark like this! 77 00:03:05,920 --> 00:03:07,715 OK, let’s get back on track. 78 00:03:07,715 --> 00:03:10,560 In a thermometer like this, the bimetallic strip 79 00:03:10,560 --> 00:03:14,498 is formed into a coil with the outside end secured in place 80 00:03:14,498 --> 00:03:17,771 and the inner part of the coil attached to a pointer. 81 00:03:17,771 --> 00:03:21,945 Although the amount the strip bends  when the temperature changes is slight, 82 00:03:21,945 --> 00:03:25,453 forming a coil compounds that effect with each rotation. 83 00:03:25,453 --> 00:03:28,427 You end up with a coil that contracts as it  gets colder, 84 00:03:28,427 --> 00:03:30,238 and expands as it gets warmer. 85 00:03:30,238 --> 00:03:32,021 Or potentially vise versa. 86 00:03:32,021 --> 00:03:36,720 And so, the center of that coil rotates somewhat as the temperature changes. 87 00:03:37,360 --> 00:03:39,804 Attach a pointer to the center of that coil, 88 00:03:39,804 --> 00:03:42,028 and with a little experimentation and calibration 89 00:03:42,028 --> 00:03:46,184 you’ll have created a simple device  which indicates the current temperature. 90 00:03:46,184 --> 00:03:48,341 The effect is surprisingly linear. 91 00:03:48,341 --> 00:03:51,835 The spacing between these numbers is consistent through most of the travel, 92 00:03:51,835 --> 00:03:54,428 although you can see it vary somewhat at the ends. 93 00:03:54,800 --> 00:03:58,081 So, if we take this thing apart through The Magic of Buying Two of Them 94 00:03:58,081 --> 00:04:01,880 we see what appears to be two bimetallic strips. 95 00:04:01,880 --> 00:04:06,333 One for the tiny, mostly useless  thermometer they give as a token gesture, 96 00:04:06,333 --> 00:04:08,357 and the other for the hygrometer. 97 00:04:08,357 --> 00:04:12,305 But this one is actually a bimetallic strip tease. 98 00:04:12,305 --> 00:04:14,575 Sure, it’s essentially the exact same idea, 99 00:04:14,575 --> 00:04:17,840 but how can two dissimilar metals give you a humidity reading? 100 00:04:18,640 --> 00:04:19,905 Well, they can’t. 101 00:04:19,905 --> 00:04:22,695 In fact not bimetallic, 102 00:04:22,695 --> 00:04:24,578 but it is bimaterial. 103 00:04:24,578 --> 00:04:27,630 Take a closer look at it and you’ll see that one side of the coil 104 00:04:27,630 --> 00:04:30,000 appears to be covered in a sort of paper. 105 00:04:30,400 --> 00:04:32,456 And that’s because it is. 106 00:04:32,456 --> 00:04:34,152 This style of hygrometer, 107 00:04:34,152 --> 00:04:37,381 fittingly named the Metal-Paper Coil hygrometer, 108 00:04:37,381 --> 00:04:41,416 functions identically to that of  a bimetallic thermometer. 109 00:04:41,416 --> 00:04:46,193 The key difference is that the salt-impregnated paper changes based on humidity. 110 00:04:46,193 --> 00:04:50,882 This is one of those things that seems puzzling at first but then absolutely obvious once you know it. 111 00:04:50,882 --> 00:04:54,111 Like, you know what happens to paper on really humid days. 112 00:04:54,111 --> 00:04:56,049 It gets all floppy and gross. 113 00:04:56,049 --> 00:04:57,646 Same sort of thing goes on here. 114 00:04:58,080 --> 00:05:02,560 The paper side of the coil will  deform slightly as humidity increases, 115 00:05:02,560 --> 00:05:05,341 changing the overall tension on the coil. 116 00:05:05,341 --> 00:05:07,527 That makes the needle move. 117 00:05:07,527 --> 00:05:10,979 Watch what happens when I put a bit of water directly on the paper. 118 00:05:10,979 --> 00:05:15,299 The coil quickly deforms and the needle shoots to “very damp.” 119 00:05:15,299 --> 00:05:19,482 And here you’ll notice that the scale is very much not linear. 120 00:05:19,482 --> 00:05:21,359 Low humidities are far apart, 121 00:05:21,359 --> 00:05:26,080 indicating that the effect of humidity on the paper diminishes as humidity increases. 122 00:05:26,640 --> 00:05:30,116 And this clock is why I decided to make this  little video. 123 00:05:30,116 --> 00:05:32,768 I bought it when I bought the other clocks for the last video 124 00:05:32,768 --> 00:05:34,538 because it would actually be useful to me 125 00:05:34,538 --> 00:05:36,684 and I had a perfect spot for it outside. 126 00:05:36,684 --> 00:05:40,448 But as soon as I realized the humidity scale was linear, 127 00:05:40,448 --> 00:05:42,998 I got suspicious of this thing. 128 00:05:42,998 --> 00:05:43,903 Sure enough, 129 00:05:43,903 --> 00:05:45,327 it’s crap. 130 00:05:45,327 --> 00:05:49,052 It agrees with this one around 50 percent or so, 131 00:05:49,052 --> 00:05:53,390 but this won’t ever read higher than maybe 80 percent? 132 00:05:53,390 --> 00:05:56,715 This one read 90 and this only read 75. 133 00:05:57,505 --> 00:05:58,236 No good. 134 00:05:58,720 --> 00:06:03,173 In fairness, metal-paper coil hygrometers aren’t super accurate to begin with. 135 00:06:03,173 --> 00:06:06,820 This website I found says they’re only good to about 10%. 136 00:06:06,820 --> 00:06:10,936 And it’s not like I could expect the hygrometer in a $10 Walmart clock 137 00:06:10,936 --> 00:06:12,726 to be any decent to begin with. 138 00:06:12,726 --> 00:06:16,397 But if you ever see a linear scale on a hygrometer like this, 139 00:06:16,880 --> 00:06:19,472 it’s definitely not one of the better ones. 140 00:06:19,930 --> 00:06:22,295 OK, well probably not - 141 00:06:22,295 --> 00:06:25,506 I haven’t yet tested this one at the time of filming. 142 00:06:25,506 --> 00:06:28,077 I’ll pin a comment with the final verdict. 143 00:06:28,077 --> 00:06:31,943 This melding of paper and metal isn’t the  only way to go about it, of course. 144 00:06:31,943 --> 00:06:35,043 In fact, it seems to be a rather new-fangled way to do it, 145 00:06:35,043 --> 00:06:38,400 presumably it’s just very easy to manufacture inexpensively. 146 00:06:39,040 --> 00:06:42,152 All you really need to make a hygrometer like this 147 00:06:42,152 --> 00:06:47,163 is some sort of spring that’s pulling on something else which will deform based on humidity. 148 00:06:47,163 --> 00:06:52,268 The first hygrometers that worked on this principle used actual human hairs. 149 00:06:52,268 --> 00:06:54,718 The hair would lengthen with increased humidity, 150 00:06:54,718 --> 00:06:57,130 reducing tension on a spring or pulley, 151 00:06:57,130 --> 00:07:00,240 and thus allowing an indicator of some kind to move. 152 00:07:00,880 --> 00:07:05,120 As it dried out, the opposite occurred and  the indicator moved in the other direction.   153 00:07:05,760 --> 00:07:10,394 This style of hygrometer is still made, but  it’s a rather specialist sort of thing. 154 00:07:10,394 --> 00:07:13,339 However, they can be quite accurate when calibrated, 155 00:07:13,339 --> 00:07:18,610 with one manufacturer claiming accuracy to within one percent at room temperatures! 156 00:07:18,610 --> 00:07:22,160 However, I found other sources which aren’t quite so optimistic. 157 00:07:22,880 --> 00:07:26,320 The worst thing about these cheap  hygrometers is their accuracy.   158 00:07:26,880 --> 00:07:30,160 While the hair-tension method  might be a little bit more accurate,   159 00:07:30,160 --> 00:07:33,580 it may still not be as accurate as you can be  with other means. 160 00:07:33,580 --> 00:07:34,661 Other means? 161 00:07:34,661 --> 00:07:36,092 What other means? 162 00:07:36,480 --> 00:07:41,093 Well, the humidistats in the humidifiers I showed  you are electronic. 163 00:07:41,093 --> 00:07:43,929 The actual component that becomes affected by humidity 164 00:07:43,929 --> 00:07:47,236 is simpler than the circuitry that interacts with it. 165 00:07:47,236 --> 00:07:52,201 Typically there will be a polymer or salt of some sort that's exposed to air, 166 00:07:52,201 --> 00:07:54,693 and the electrical resistance of this material 167 00:07:54,693 --> 00:07:59,031 changes with the moisture absorbed in it and thus the ambient humidity. 168 00:07:59,031 --> 00:08:02,137 Measure its resistance, compare that to a lookup table, 169 00:08:02,137 --> 00:08:05,386 and now you know the relative humidity within a few percentage points. 170 00:08:05,520 --> 00:08:09,600 These days this rather basic task  can be done at the component level,   171 00:08:09,600 --> 00:08:14,000 allowing a simple interface between a sensor  and whatever device you’re putting it in. 172 00:08:14,560 --> 00:08:19,280 There are other techniques involving materials  which exhibit changes in their capacitance,   173 00:08:19,280 --> 00:08:22,400 but the essence of all of them  is in the material which changes   174 00:08:22,400 --> 00:08:25,227 in some way depending on ambient humidity. 175 00:08:25,227 --> 00:08:27,667 It can be something we measure electrically, 176 00:08:27,667 --> 00:08:32,419 or it can be something that moves a pointer like  a piece of paper or a human hair. 177 00:08:32,419 --> 00:08:34,365 What we’ve done with these devices, 178 00:08:34,365 --> 00:08:35,838 including the thermometers, 179 00:08:35,838 --> 00:08:38,897 is quite simple but also quite profound. 180 00:08:38,897 --> 00:08:43,214 Figuring out how environmental conditions affect different  materials 181 00:08:43,214 --> 00:08:49,884 allowed us to work backwards and define those environmental conditions using the material as a reference. 182 00:08:49,884 --> 00:08:51,840 Those humans, so clever! 183 00:08:52,560 --> 00:08:56,326 While it may be more technically impressive to  do that using electronicals 184 00:08:56,326 --> 00:08:58,932 and hook it up to a microcontroller which can beam 185 00:08:58,932 --> 00:09:01,440 god-awful blue numbers straight into your retinas, 186 00:09:02,400 --> 00:09:06,563 that’s just not as satisfying as these simple things. 187 00:09:06,563 --> 00:09:09,633 Turning the physical properties of something into a, 188 00:09:09,838 --> 00:09:13,040 well, turning motion is never gonna get old to me. 189 00:09:13,920 --> 00:09:15,803 I told you it’d be simple! 190 00:09:15,803 --> 00:09:20,825 Now I’ll have fun looking at the YouTube studio and seeing my watch time metric tank. 191 00:09:20,825 --> 00:09:21,840 It’ll be great. 192 00:09:23,760 --> 00:09:28,128 Oh yeah, sorry. No music or  credits today. Just… 193 00:09:28,128 --> 00:09:28,628 this. 194 00:09:30,534 --> 00:09:33,330 Take a closer look, and you'll see that one of zah 195 00:09:33,330 --> 00:09:34,300 elbledebuh be deh. 196 00:09:34,300 --> 00:09:35,041 plerh