1 00:00:00,080 --> 00:00:03,929 In my last video, we explored how analog television works. 2 00:00:03,929 --> 00:00:07,430 You can check out the whole video either through this card or through the link in the description, 3 00:00:07,430 --> 00:00:09,550 but here’s a brief overview. 4 00:00:09,550 --> 00:00:14,550 At its core, analog television is just an amplitude modulated radio transmission where 5 00:00:14,550 --> 00:00:18,820 the strength of the signal dictates brightness of a light source, with a strong signal producing 6 00:00:18,820 --> 00:00:22,060 a bright light, and a weak signal producing little to no light. 7 00:00:22,060 --> 00:00:26,160 The television set uses an electromagnet to deflect the source of the light, an electron 8 00:00:26,160 --> 00:00:31,050 beam, in a pattern called a raster, which is really just a ton of horizontal lines. 9 00:00:31,050 --> 00:00:35,470 This has the effect of producing a glowing series of lines on the face of a picture tube. 10 00:00:35,470 --> 00:00:39,410 The electronics of the TV set line up the incoming signal with the movement of the beam 11 00:00:39,410 --> 00:00:43,640 to create an image, with each part of the imaging being drawn brightly or darkly along 12 00:00:43,640 --> 00:00:46,090 with the signal’s instantaneous strength. 13 00:00:46,090 --> 00:00:48,540 With everything in alignment, you get an image. 14 00:00:48,540 --> 00:00:52,920 By far the most complicated part of making an image appear on the screen is making that 15 00:00:52,920 --> 00:00:54,480 raster pattern. 16 00:00:54,480 --> 00:00:58,210 The electronic components and other crucial parts such as the picture tube and deflection 17 00:00:58,210 --> 00:01:02,630 yoke are primitive by today’s standards, but still pretty complicated. 18 00:01:02,630 --> 00:01:06,350 We really just need a way make a repeating pattern of lines from a light source, there’s 19 00:01:06,350 --> 00:01:08,830 got to be a simpler way to do it! 20 00:01:08,830 --> 00:01:10,740 Enter: Mechanical Television. 21 00:01:10,740 --> 00:01:15,720 The earliest televisions actually got some of their inspiration from fax machines, really?, 22 00:01:15,720 --> 00:01:18,060 and relied on a couple of important developments. 23 00:01:18,060 --> 00:01:21,180 So first a bit about the fax machines. 24 00:01:21,180 --> 00:01:24,710 Facsimile transmission actually predates the telephone? 25 00:01:24,710 --> 00:01:29,350 (what?), with images such as signatures being commercially reproduced over telegraph wires 26 00:01:29,350 --> 00:01:34,930 as far back as 1865, and the earliest fax-like device being invented by Scottish inventor 27 00:01:34,930 --> 00:01:36,910 Alexander Bain in 1846. 28 00:01:36,910 --> 00:01:41,540 Now, I’m simplifying a great deal here, but the theory was that if you could synchronize 29 00:01:41,540 --> 00:01:46,200 the movement of a scanning device with a drawing device, you could replicate an image. 30 00:01:46,200 --> 00:01:50,250 If you scanned a piece of paper line by line and sent a signal over a wire to match the 31 00:01:50,250 --> 00:01:54,590 darkness of the ink, you could reproduce the image by syncing up a drawing mechanism with 32 00:01:54,590 --> 00:01:56,100 the scanning one. 33 00:01:56,100 --> 00:01:59,400 These early fax machines worked, but they were very slow. 34 00:01:59,400 --> 00:02:03,950 Nevertheless, they showed us that you could, via electro-mechanical means, reproduce an 35 00:02:03,950 --> 00:02:04,950 image. 36 00:02:04,950 --> 00:02:10,690 Fast forward to 1884, and 23-year old Paul Julius Gottlieb Nipkow created the Nipkow 37 00:02:10,690 --> 00:02:11,690 disc. 38 00:02:11,690 --> 00:02:14,610 This is the core of most mechanical television systems. 39 00:02:14,610 --> 00:02:19,550 Nipkow realized that a spinning disc could methodically scan an image line-by-line simply 40 00:02:19,550 --> 00:02:23,050 by placing evenly-spaced holes in a spiral pattern. 41 00:02:23,050 --> 00:02:24,490 This is a home-made Nipkow disc. 42 00:02:24,490 --> 00:02:29,590 I took a really awful vinyl record that I’d be happy to destroy, and marked 32 divisions 43 00:02:29,590 --> 00:02:33,730 around the circumference, like 32 very skinny pie slices. 44 00:02:33,730 --> 00:02:38,020 Then I methodically drilled a hole along these lines, with each hole being drilled a 32nd 45 00:02:38,020 --> 00:02:42,440 of an inch (roughly .8 milimeters) closer to the center than the last. 46 00:02:42,440 --> 00:02:44,940 The result is a spiral pattern of holes. 47 00:02:44,940 --> 00:02:48,450 This might not seem like much, but it’s actually extremely clever. 48 00:02:48,450 --> 00:02:53,110 If you put a square-ish shaped mask in front of the holes, its height being slightly less 49 00:02:53,110 --> 00:02:57,110 than the distance between the holes, you’ve made a device which mechanically creates a 50 00:02:57,110 --> 00:02:59,940 raster scan using these physical holes. 51 00:02:59,940 --> 00:03:04,901 John Logie Baird realized that with this Nipkow disc, you could in theory focus an image with 52 00:03:04,901 --> 00:03:09,340 a lens onto the disc, and you could use a light sensor to give an instantaneous reading 53 00:03:09,340 --> 00:03:13,510 of how bright each part of the image was, with the holes in the nipkow disc serving 54 00:03:13,510 --> 00:03:16,770 as a way to divide the image into transmittable pieces. 55 00:03:16,770 --> 00:03:21,870 Back in 1873, Willoughby Smith discovered the photoconductivity of selenium, and with 56 00:03:21,870 --> 00:03:26,500 this knowledge Baird used some selenium to create the light sensor for his televisor. 57 00:03:26,500 --> 00:03:31,599 I’ve mounted this Nipkow disc to an AC motor which will spin it at 1,800 RPM, giving a 58 00:03:31,599 --> 00:03:34,640 complete revolution 30 times per second. 59 00:03:34,640 --> 00:03:36,480 Before I turn it on, look through the mask. 60 00:03:36,480 --> 00:03:41,020 I’ve put an extremely bright LED behind the disc so you can see the holes. 61 00:03:41,020 --> 00:03:45,209 As I slowly turn the disc, you’ll see that only one hole is visible at a time, and each 62 00:03:45,209 --> 00:03:48,110 hole gets closer to the left than the next one. 63 00:03:48,110 --> 00:03:52,460 When I switch the motor on, the holes blend into a moving line, and as it gets faster, 64 00:03:52,460 --> 00:03:55,069 the line seems to widen into a square. 65 00:03:55,069 --> 00:03:59,099 This square is very uneven because my homemade Nipkow disc was made hastily and with poor 66 00:03:59,099 --> 00:04:00,099 precision. 67 00:04:00,099 --> 00:04:01,099 But here’s the key. 68 00:04:01,099 --> 00:04:04,230 Only one of the holes is actually visible through the mask at any given moment. 69 00:04:04,230 --> 00:04:06,660 It’s just moving too fast to see. 70 00:04:06,660 --> 00:04:11,180 Baird used the selenium light sensor to create a signal from an image being scanned by the 71 00:04:11,180 --> 00:04:15,950 disc, and on the receiving end, another identical disc would spin at precisely the same speed, 72 00:04:15,950 --> 00:04:20,280 and a light source such as a neon lamp would vary its brightness along with the signal 73 00:04:20,280 --> 00:04:24,599 strength presented by the light sensor, and thus, you’d get an image. 74 00:04:24,599 --> 00:04:27,289 I shall now attempt to show you how this worked. 75 00:04:27,289 --> 00:04:30,990 Now before you get too excited, I’ll admit that my mechanical television doesn’t work 76 00:04:30,990 --> 00:04:32,059 as well as I had hoped. 77 00:04:32,059 --> 00:04:35,599 And that’s all on my insistence in using crap I had laying around, rather than going 78 00:04:35,599 --> 00:04:37,779 through the process to make a proper LED driver. 79 00:04:37,779 --> 00:04:41,900 However, I hope you’ll get an understanding of what’s going on. 80 00:04:41,900 --> 00:04:45,099 This 10W LED chip is what we’ll use as a light source. 81 00:04:45,099 --> 00:04:49,680 It’s really bright and, importantly, it can react very quickly to changes in the voltage 82 00:04:49,680 --> 00:04:50,680 it receives. 83 00:04:50,680 --> 00:04:54,050 First, I’ll simply power the LED continuously. 84 00:04:54,050 --> 00:04:57,780 As the disc spins up, the lines start to blend into each other, and eventually the whole 85 00:04:57,780 --> 00:04:59,580 “screen” is illuminated. 86 00:04:59,580 --> 00:05:04,249 Now, I’m going to switch the LED on and off at a higher and higher frequency. 87 00:05:04,249 --> 00:05:06,110 First, 5 hz. 88 00:05:06,110 --> 00:05:09,879 The screen appears to just be flashing, nothing too extraordinary, but you might be able to 89 00:05:09,879 --> 00:05:12,909 see some odd stuff happening as the light switches states. 90 00:05:12,909 --> 00:05:15,779 Now I’ll switch it on and off at 60 hz. 91 00:05:15,779 --> 00:05:17,639 Something odd starts to be visible here. 92 00:05:17,639 --> 00:05:21,809 See, the disc makes a complete revolution 30 times per second, and with the light flashing 93 00:05:21,809 --> 00:05:26,059 at twice that frequency, only some of the holes are lit up as the disc passes over the 94 00:05:26,059 --> 00:05:27,219 LED. 95 00:05:27,219 --> 00:05:29,719 Now let’s move to 1,800 hz. 96 00:05:29,719 --> 00:05:33,469 Frequencies that are a multiple of 30 will appear stable as an even number of pulses 97 00:05:33,469 --> 00:05:35,289 fit within each revolution. 98 00:05:35,289 --> 00:05:38,110 If you mess with that, though, things get weird. 99 00:05:38,110 --> 00:05:42,530 Bumping the frequency up just a tad makes the pattern move in relation to the disc. 100 00:05:42,530 --> 00:05:46,809 The holes in the disc are directly responsible for creating the patterns you see. 101 00:05:46,809 --> 00:05:50,189 Without the disc, the LED appears to just be continuously illuminated. 102 00:05:50,189 --> 00:05:51,189 But, it’s not. 103 00:05:51,189 --> 00:05:53,469 It’s flashing really quickly. 104 00:05:53,469 --> 00:05:57,819 The disc allows for that flashing to be visible because it physically obscures different parts 105 00:05:57,819 --> 00:05:59,889 of the light source over time. 106 00:05:59,889 --> 00:06:04,059 This is just like the electron beam in the CRT television, except instead of electromagnets 107 00:06:04,059 --> 00:06:08,479 moving a beam across the surface of a picture tube, the light source is physically moved 108 00:06:08,479 --> 00:06:10,180 via the location of these holes. 109 00:06:10,180 --> 00:06:14,860 It’s a pretty crafty way of producing a raster scan, and it actually works. 110 00:06:14,860 --> 00:06:18,280 This is the best imagery I could get my televisor to produce. 111 00:06:18,280 --> 00:06:22,099 This pattern was generated through manipulating audio samples in Audacity. 112 00:06:22,099 --> 00:06:26,969 To give you an idea of how poorly this mechanical TV works, well the image I intended to make 113 00:06:26,969 --> 00:06:31,219 was not a map of the world as this vaguely suggests, but that of a circle. 114 00:06:31,219 --> 00:06:33,710 Here’s a look at true video. 115 00:06:33,710 --> 00:06:38,259 What you’re seeing here is a very low contrast, very low resolution image of Seth Meyers. 116 00:06:38,259 --> 00:06:42,130 I mean obviously, how could you not recognize him? 117 00:06:42,130 --> 00:06:46,289 Yeah OK, it’s garbage, but you can see that there is certainly something there and it’s 118 00:06:46,289 --> 00:06:47,430 moving slightly. 119 00:06:47,430 --> 00:06:51,080 Like a talk show host’s head might when said talk show host is talking. 120 00:06:51,080 --> 00:06:52,180 On his show. 121 00:06:52,180 --> 00:06:56,599 To make this image, I simply placed my phone behind the televisor with the screen brightness 122 00:06:56,599 --> 00:07:01,650 all the way up, and I placed this solar panel with an audio cord patched into it into one 123 00:07:01,650 --> 00:07:05,689 of my trusty Tascam DR-05 audio recorders, which I use all the time. 124 00:07:05,689 --> 00:07:08,229 In fact there’s one in my pocket right now. 125 00:07:08,229 --> 00:07:11,020 And yes, that’s directly from a solar garden light. 126 00:07:11,020 --> 00:07:14,919 The solar panel would produce a high current whenever it saw bright light, and it would 127 00:07:14,919 --> 00:07:17,409 produce low current with less light. 128 00:07:17,409 --> 00:07:18,429 Duh. 129 00:07:18,429 --> 00:07:22,369 As the disc spun, it would only allow the tiniest bit of the image through to the solar 130 00:07:22,369 --> 00:07:24,639 panel at any given time. 131 00:07:24,639 --> 00:07:29,050 This would produce a quickly varying signal with amplitude corresponding to image brightness. 132 00:07:29,050 --> 00:07:33,559 The TASCAM would just encode these relative brightnesses as sound samples, at a sample 133 00:07:33,559 --> 00:07:38,759 rate of 48 kilohertz, and then because I’m really lazy, I just hooked my LED into an 134 00:07:38,759 --> 00:07:41,770 audio amplifier and played that sound back. 135 00:07:41,770 --> 00:07:45,779 The LED would become brighter with a stronger signal from the amplifier, though as it’s 136 00:07:45,779 --> 00:07:49,449 a diode it would filter out any AC components of the signal. 137 00:07:49,449 --> 00:07:52,679 Quite honestly I’m amazed it produces anything at all. 138 00:07:52,679 --> 00:07:58,339 I opened the file in Audacity just to see what it looked like, and it’s pretty intriguing. 139 00:07:58,339 --> 00:08:15,089 Here’s what it sounds like, for those interested. 140 00:08:15,089 --> 00:08:26,750 Now, in case it’s not obvious, let’s go over the reasons mechanical television didn’t 141 00:08:26,750 --> 00:08:27,750 catch on. 142 00:08:27,750 --> 00:08:31,300 First, up until now, I’ve not let you hear what this sounds like. 143 00:08:31,300 --> 00:08:35,880 Here’s what a 12 inch vinyl disc sounds like at 1,800 RPM. 144 00:08:47,000 --> 00:08:49,120 I’m sure that would never get old. 145 00:08:49,150 --> 00:08:54,280 But aside from that, there are just so many practical concerns with mechanical TV. 146 00:08:54,280 --> 00:08:55,490 First of all, the image is tiny. 147 00:08:55,490 --> 00:08:59,160 And it’s a horribly low resolution--only 32 lines. 148 00:08:59,160 --> 00:09:03,180 That’s the only reason a signal can be recorded as an audio file. 149 00:09:03,180 --> 00:09:05,150 Not a lot of bandwidth is needed. 150 00:09:05,150 --> 00:09:09,840 Because the disc obscures almost all of the light source, hardly any light gets through. 151 00:09:09,840 --> 00:09:14,900 This LED is fricken bright, it’s painful to look at directly, and yet through the Nipkow 152 00:09:14,900 --> 00:09:18,900 disc, nearly all of the light is blocked, and it produces a dull image. 153 00:09:18,900 --> 00:09:23,200 When these devices were first in development, the light source would often be a neon lamp, 154 00:09:23,200 --> 00:09:25,630 like the orange light in a powerstrip’s switch. 155 00:09:25,630 --> 00:09:29,090 Imagine how dark the image would be with only that for a light source. 156 00:09:29,090 --> 00:09:33,340 One of the biggest troubles with mechanical television is image synchronization. 157 00:09:33,340 --> 00:09:37,021 Because we’re using a big spinning thing to divide the light into chunks, the disc 158 00:09:37,021 --> 00:09:42,060 has to be in precisely the right place if you want the image to land where it should. 159 00:09:42,060 --> 00:09:46,730 If we take the mask away, you can see that the image just repeats itself over and over. 160 00:09:46,730 --> 00:09:50,930 But each adjacent image is actually shifted one line up or down. 161 00:09:50,930 --> 00:09:55,110 The most critical part of synchronization was ensuring the disc is spinning at the exact 162 00:09:55,110 --> 00:09:59,630 same speed as the scanning disc of a camera, but it would also be necessary to slow down 163 00:09:59,630 --> 00:10:03,630 or speed up the disc in slight increments to get the image aligned with the viewing 164 00:10:03,630 --> 00:10:06,930 mask, and with the top and bottom in the right place. 165 00:10:06,930 --> 00:10:10,700 But the most damning problem is that of geometry. 166 00:10:10,700 --> 00:10:15,830 Imagine we wanted to make a display with the resolution and size of this small CRT television. 167 00:10:15,830 --> 00:10:19,250 Well, the face of the tube is about 15 cm wide. 168 00:10:19,250 --> 00:10:24,250 With 480 lines of resolution, there would need to be 480 holes in the nipkow disc. 169 00:10:24,250 --> 00:10:28,060 Remember, only one hole can be seen through the mask at once for this to work, so the 170 00:10:28,060 --> 00:10:31,850 holes have to be at a minimum 15 centimeters apart. 171 00:10:31,850 --> 00:10:35,930 So the disc’s circumference would have to be 72 meters, with a diameter of roughly 23 172 00:10:35,930 --> 00:10:38,290 meters, or about 75 feet. 173 00:10:38,290 --> 00:10:40,460 I live in a building that’s 6 stories tall. 174 00:10:40,460 --> 00:10:44,180 A mechanical television to rival this TV would be taller than my building! 175 00:10:44,180 --> 00:10:49,090 And, it would have to spin at 1,800 RPM just like this one to make 30 frames per second 176 00:10:49,090 --> 00:10:50,130 possible. 177 00:10:50,130 --> 00:10:51,790 This things scares me spinning this fast. 178 00:10:51,790 --> 00:10:54,940 I’m pretty sure a 75 foot disc would just explode. 179 00:10:54,940 --> 00:10:56,380 In fact, let’s do the math. 180 00:10:56,380 --> 00:11:01,950 A 72 meter circumference means that the edge of the disc would travel 2.160 kilometers 181 00:11:01,950 --> 00:11:05,790 per second, or well above mach 6. 182 00:11:05,790 --> 00:11:06,980 Yeah. 183 00:11:06,980 --> 00:11:10,740 If the disc were rolling, it would make it from New York to Los Angeles in about 35 minutes--not 184 00:11:10,740 --> 00:11:14,610 in a straight line, mind you, but by traveling along actual roads. 185 00:11:14,610 --> 00:11:17,900 So, the Baird television system didn’t get too far. 186 00:11:17,900 --> 00:11:22,110 It was certainly genious and is an important part of the history of television. 187 00:11:22,110 --> 00:11:26,740 But is was far too limited, clunky, and, to be honest, it had crappy image quality. 188 00:11:26,740 --> 00:11:31,490 I’ve added some links in the description to videos of mechanical televisions that actually 189 00:11:31,490 --> 00:11:34,820 work, and I think you’ll agree that’s they’re pretty cool, but it’s a damn good 190 00:11:34,820 --> 00:11:37,220 thing they didn’t become mainstream. 191 00:11:37,220 --> 00:11:39,750 As always, thank you so much for watching. 192 00:11:39,750 --> 00:11:42,610 If you liked this video, a thumbs up would be most appreciated. 193 00:11:42,610 --> 00:11:47,680 I’m absolutely thrilled that this channel has over 21,000 subscribers now! 194 00:11:47,680 --> 00:11:49,680 I never thought that would be possibl. 195 00:11:49,680 --> 00:11:53,360 If you’re not one of the people in that number, and you 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