00:00:01.380 [Music] 00:00:11.41000:00:11.420 g'day and welcome back to RC model 00:00:13.64000:00:13.650 reviews another tick Tuesday for the 00:00:16.01000:00:16.020 sixth November 2018 and today I'm 00:00:18.62000:00:18.630 talking about capacitors now I said I 00:00:20.06000:00:20.070 was going to talk about accelerometers 00:00:21.65000:00:21.660 but I've decided to leave that till next 00:00:22.93900:00:22.949 week because then we do something 00:00:24.89000:00:24.900 different you know changes as good as a 00:00:26.35900:00:26.369 holiday let's have a holiday let's 00:00:27.71000:00:27.720 change it to talk about something that's 00:00:29.00000:00:29.010 really quite simple it is what we call a 00:00:31.16000:00:31.170 passive component and they're one of the 00:00:33.11000:00:33.120 building blocks of all the electronic 00:00:34.58000:00:34.590 devices that we have in the Hobby 00:00:36.10000:00:36.110 capacitors are an essential building 00:00:38.24000:00:38.250 block the basic the basic passives are 00:00:40.33000:00:40.340 capacitors resistors and inductors and 00:00:42.68000:00:42.690 they're called passives because they 00:00:44.33000:00:44.340 just lie around doing nothing they don't 00:00:46.06900:00:46.079 have any active elements as to say they 00:00:48.35000:00:48.360 are would you say they don't amplify 00:00:50.95900:00:50.969 anything they simply change the way the 00:00:53.45000:00:53.460 electricity flows but they don't change 00:00:55.45900:00:55.469 it in an active way they passively 00:00:57.41000:00:57.420 change it that didn't explain to them 00:00:58.93900:00:58.949 thing that never mind let's move on 00:01:00.22900:01:00.239 capacitors and this is this circuit 00:01:02.42000:01:02.430 diagram for a compare the elta 00:01:04.72900:01:04.739 symbol for a capacitor in a circuit 00:01:06.50000:01:06.510 diagram and it tells us a lot about 00:01:09.02000:01:09.030 capacitors actually because what the 00:01:10.52000:01:10.530 capacitors are really is just two plates 00:01:12.20000:01:12.210 of conductive materials separated by an 00:01:14.39000:01:14.400 insulator that insulator can be here it 00:01:17.24000:01:17.250 can be plastic it can be a liquid it 00:01:19.70000:01:19.710 just it can be an oxide of metal it'll 00:01:21.38000:01:21.390 be anything that doesn't conduct 00:01:22.91000:01:22.920 electricity which is basically what an 00:01:24.83000:01:24.840 insulator is isn't it so that's what a 00:01:26.92900:01:26.939 capacitor is capacitors are measured 00:01:29.60000:01:29.610 there's two values for a capacitor one 00:01:32.63000:01:32.640 is the voltage rating because as you can 00:01:35.51000:01:35.520 see if this is a good insulator and here 00:01:38.48000:01:38.490 you put voltage on one side and the 00:01:40.88000:01:40.890 other voltage you know like positive on 00:01:42.23000:01:42.240 here and negative on there if you put 00:01:43.63900:01:43.649 enough voltage then a spark will jump 00:01:45.23000:01:45.240 through here or even with a plastic 00:01:46.96900:01:46.979 insulator the plastic will break down 00:01:48.41000:01:48.420 and you'll get electricity jumping 00:01:50.71900:01:50.729 between the plates and that's when they 00:01:52.06900:01:52.079 file it can produce a short-circuit so 00:01:54.41000:01:54.420 you need to write the voltage that 00:01:55.96900:01:55.979 maximum voltage capacitor can handle if 00:01:57.80000:01:57.810 you use a voltage capacitor with two 00:01:59.33000:01:59.340 lower voltage rating then the insulating 00:02:01.49000:02:01.500 layer will break down and sometimes 00:02:03.41000:02:03.420 magic smoke will come out so the voltage 00:02:06.17000:02:06.180 rating is probably you know in terms of 00:02:08.60000:02:08.610 longevity that's a really important 00:02:10.33900:02:10.349 thing now the other rating is the 00:02:12.11000:02:12.120 capacity of the capacitor 00:02:13.79000:02:13.800 but go capacitors because they have a 00:02:15.20000:02:15.210 capacity and that's measured in farad's 00:02:17.78000:02:17.790 that's the unit of measurement but a 00:02:19.49000:02:19.500 farad is a huge amount of capacity so 00:02:21.92000:02:21.930 normally we talk about them and things 00:02:23.36000:02:23.370 like micro farad's 00:02:25.70000:02:25.710 nano farad's or pico farads so there are 00:02:28.67000:02:28.680 all tiny fractions of a farad obviously 00:02:30.59000:02:30.600 if you look up those there's prefixes 00:02:32.42000:02:32.430 you work at what they are you know micro 00:02:33.95000:02:33.960 is one millionth nano is one billionth 00:02:36.53000:02:36.540 and pico is 1,000 billion for whatever 00:02:38.78000:02:38.790 so yes so we're dealing with very small 00:02:42.35000:02:42.360 amounts now when I say farad's you know 00:02:46.79000:02:46.800 don't you dear Ferris would say she 00:02:48.17000:02:48.180 sometimes you do because there's a thing 00:02:49.70000:02:49.710 called a super cap which is really 00:02:51.62000:02:51.630 really really just check my notes really 00:02:54.11000:02:54.120 high capacity capacitor and sometimes 00:02:56.30000:02:56.310 they're measured in farad's I'll talk 00:02:57.50000:02:57.510 about those a bit more in a moment but 00:02:59.39000:02:59.400 here we go there's a competitor there's 00:03:01.04000:03:01.050 the symbol and how do they work well 00:03:02.57000:03:02.580 I'll just show you basically they are 00:03:04.73000:03:04.740 like a reservoir of electricity you can 00:03:07.01000:03:07.020 temporarily store electricity capacitor 00:03:09.35000:03:09.360 and then pull it out again it's one of 00:03:11.81000:03:11.820 the most common uses for a capacitor 00:03:13.28000:03:13.290 that because the reservoir of 00:03:14.36000:03:14.370 electricity no not like a battery though 00:03:16.82000:03:16.830 because batteries don't store electrons 00:03:19.76000:03:19.770 they store chemical energy they convert 00:03:22.22000:03:22.230 the flow of electricity into a chemical 00:03:24.32000:03:24.330 energy that can then be reversed in 00:03:26.66000:03:26.670 therefore the electrons come back out 00:03:27.83000:03:27.840 again making electrical circuit so these 00:03:30.77000:03:30.780 have no chemical actions are stalkers 00:03:33.26000:03:33.270 are completely passive there's no 00:03:34.69900:03:34.709 chemical reactions it's just a buildup 00:03:36.80000:03:36.810 of electrons on one plate and a lack of 00:03:38.33000:03:38.340 electrons on the other place so if we 00:03:39.74000:03:39.750 were to connect this up to a battery 00:03:40.69900:03:40.709 let's say we had a battery here it had a 00:03:41.87000:03:41.880 positive terminal a negative terminal 00:03:43.34000:03:43.350 and we ran a wire from the positive to 00:03:45.92000:03:45.930 there and from the negative to there 00:03:49.36000:03:49.370 what would happen here is actually 00:03:51.29000:03:51.300 really interesting opposites attract 00:03:53.93000:03:53.940 that's why ugly women like me okay but 00:03:57.19900:03:57.209 opposites attract so what happens here 00:03:58.31000:03:58.320 is on the positive terminal here that 00:03:59.96000:03:59.970 will actually attract but normally 00:04:01.52000:04:01.530 speaking you've got electrons on both 00:04:02.96000:04:02.970 sides of these plates right just a few 00:04:04.46000:04:04.470 electrons if you can eat up to a battery 00:04:07.13000:04:07.140 the electrons on this plate are 00:04:08.96000:04:08.970 attracted to the positive terminal so 00:04:10.49000:04:10.500 you end up losing electrons from this 00:04:13.16000:04:13.170 plate and and because of the way things 00:04:18.25900:04:18.269 are going electricity flows in a circuit 00:04:20.53900:04:20.549 so you have electrons traveling up this 00:04:21.89000:04:21.900 way and you have extra electrons 00:04:23.96000:04:23.970 arriving on that plate so you have a 00:04:25.19000:04:25.200 capacitor is charged 00:04:26.61000:04:26.620 with electrons less toward the plates 00:04:28.74000:04:28.750 control it hold the electrons no 00:04:30.00000:04:30.010 chemical stuff it's just raw electrons 00:04:31.74000:04:31.750 stored inside your capacitor and that 00:04:34.47000:04:34.480 has a number of benefits over a battery 00:04:35.90900:04:35.919 obviously because chemical reactions 00:04:38.21900:04:38.229 break down over time you know 00:04:39.24000:04:39.250 chemistry's the for example it's take a 00:04:41.82000:04:41.830 lead acid battery the acid goes you know 00:04:45.99000:04:46.000 get contaminated the lead forms sulfates 00:04:49.26000:04:49.270 and then breaks down forms a layer on 00:04:51.62900:04:51.639 the bottom which shorts out the place so 00:04:53.15900:04:53.169 many think bad things can happen with 00:04:54.57000:04:54.580 batteries but with a capacitor there's 00:04:57.30000:04:57.310 nothing chemical happening so they would 00:04:58.77000:04:58.780 in theory last a long long long long 00:05:00.39000:05:00.400 long time 00:05:01.62000:05:01.630 they don't always they'll get on to that 00:05:03.62900:05:03.639 later on but up also because you're not 00:05:05.94000:05:05.950 having to wait for a chemical reaction 00:05:07.05000:05:07.060 to take place you know when you charge 00:05:08.37000:05:08.380 your life or you charge it at 1 C and it 00:05:10.59000:05:10.600 takes an hour it takes over an hour to 00:05:12.21000:05:12.220 actually charge that battery because you 00:05:13.62000:05:13.630 can't charge it too fast if you tried to 00:05:15.21000:05:15.220 charge it 100 C it explode because the 00:05:17.94000:05:17.950 electrons would rush in the chemical 00:05:19.98000:05:19.990 reaction would take place but then it 00:05:21.62900:05:21.639 protects place so quickly that gas is 00:05:23.94000:05:23.950 liberated that the electrolyte and the 00:05:25.26000:05:25.270 battery boils and then the guests 00:05:27.09000:05:27.100 pressurize it and then boom you're going 00:05:28.83000:05:28.840 to be explosion with capacitor none of 00:05:31.56000:05:31.570 that carry on it'll accept electrons as 00:05:33.62900:05:33.639 as as quickly as you like the limit 00:05:36.21000:05:36.220 being basically the wires that connect 00:05:38.58000:05:38.590 in the plates if they just pass too much 00:05:40.02000:05:40.030 can't they'll get hot and melt it's 00:05:41.55000:05:41.560 really the basic limit so you can charge 00:05:43.50000:05:43.510 capacitors really quickly and you can 00:05:45.51000:05:45.520 discharge them really quickly which 00:05:48.62900:05:48.639 brings us to this thing is what's that 00:05:50.94000:05:50.950 it's called effectively series resistant 00:05:53.21900:05:53.229 now as I mentioned the only limiting 00:05:56.31000:05:56.320 factor in charging your capacitor is how 00:05:58.26000:05:58.270 much current the wires and the plates 00:05:59.67000:05:59.680 can handle before they become fuses and 00:06:01.62000:06:01.630 melt and because everything that 00:06:03.83900:06:03.849 conducts electricity 00:06:04.92000:06:04.930 apart from superconductors and we're not 00:06:06.57000:06:06.580 going there has a resistance so in 00:06:09.12000:06:09.130 theory if we were to draw this there's 00:06:10.58900:06:10.599 actually what we call a parasitic 00:06:13.02000:06:13.030 resistance in the capacitor if this is a 00:06:15.44000:06:15.450 capacitor there's a resistor in there 00:06:17.67000:06:17.680 and it's actually just the resistance of 00:06:18.96000:06:18.970 the wires and the plates and what 00:06:21.36000:06:21.370 happens is that resistance can reduce 00:06:23.96900:06:23.979 the efficiency of the capacitor to take 00:06:25.95000:06:25.960 large amounts of current and deliver 00:06:27.18000:06:27.190 large amounts of current so we want to 00:06:28.86000:06:28.870 do that we want to be able to charge it 00:06:30.36000:06:30.370 and discharge it very quickly and have 00:06:31.58900:06:31.599 it handled very high flows of current in 00:06:33.81000:06:33.820 and out we need a capacitor which has a 00:06:35.01000:06:35.020 low effective series resistance it's 00:06:37.11000:06:37.120 this thing in here and that enables it 00:06:39.24000:06:39.250 to work far more efficiently and 00:06:40.37900:06:40.389 high-current high flow situations and 00:06:43.40900:06:43.419 one of those is let me show you when 00:06:45.51000:06:45.520 you'd use a high ESR capacitor actually 00:06:47.61000:06:47.620 I mean a low ear side capacitor 00:06:49.26000:06:49.270 capacitor capacitor with a low effective 00:06:51.57000:06:51.580 series resistance one that looks able to 00:06:54.20900:06:54.219 handle lots of current here is a typical 00:06:55.83000:06:55.840 setup when you might want to use a 00:06:56.76000:06:56.770 capacitor this is a battery lipo there's 00:06:59.12900:06:59.139 an ESC there's your motor yes pretty 00:07:01.08000:07:01.090 standard stuff isn't it 00:07:02.04000:07:02.050 now his as well as powering the ESC in 00:07:04.92000:07:04.930 the motor the battery may be providing 00:07:07.23000:07:07.240 voltage to a video transmitter and a 00:07:09.20900:07:09.219 camera let's put an aerial on the video 00:07:11.01000:07:11.020 transmitter before it burns out okay and 00:07:15.14000:07:15.150 bad things can happen here this is if 00:07:17.87900:07:17.889 you were around in the early days of 00:07:19.55900:07:19.569 many quads and things you'll know that 00:07:20.64000:07:20.650 it was really common to get really bad 00:07:22.64900:07:22.659 lines on the video when you had your 00:07:24.83900:07:24.849 motors when you're out of something the 00:07:26.24900:07:26.259 video to old crap either be lines all 00:07:27.86900:07:27.879 the way through the reason for that is 00:07:29.39900:07:29.409 that inside the ESC there are little 00:07:32.51900:07:32.529 tiny solar states which is called Fitz 00:07:34.32000:07:34.330 which we'll cover in a future video 00:07:35.33900:07:35.349 which are basically turning off and on 00:07:37.14000:07:37.150 the current going to the windings around 00:07:38.99900:07:39.009 the around the motor there on the stator 00:07:41.55000:07:41.560 of the motor so those voltage those 00:07:43.37900:07:43.389 currents are being switched very quickly 00:07:44.70000:07:44.710 and that means the load on the battery 00:07:46.76000:07:46.770 through the ESC is varying quite 00:07:49.37900:07:49.389 significantly as one core gets turned on 00:07:50.99900:07:51.009 there's more current drawn and then it 00:07:53.12900:07:53.139 gets turned off and another one gets 00:07:54.14900:07:54.159 turned on and with batteries as we 00:07:56.01000:07:56.020 probably already know when you put a 00:07:57.74900:07:57.759 load on the battery the voltage drops 00:07:59.51900:07:59.529 its natural it's just because again 00:08:02.39900:08:02.409 there's a parasitic resistor inside the 00:08:04.11000:08:04.120 battery you know and there's the 00:08:05.45900:08:05.469 internal resistance of the battery and 00:08:06.93000:08:06.940 when you put a load on it some of the 00:08:08.51900:08:08.529 voltage gets dropped across the internal 00:08:10.14000:08:10.150 resistance it's not a real resistor so a 00:08:11.87900:08:11.889 theoretical one but that voltage 00:08:13.43900:08:13.449 disappears across there so if we would 00:08:15.32900:08:15.339 have put an oscilloscope here 00:08:16.64900:08:16.659 let's have a look it's getting 00:08:18.99000:08:19.000 oscilloscope I should actually do this 00:08:20.99900:08:21.009 on the bench shouldn't I okay and here 00:08:23.21900:08:23.229 is the oscilloscope it's put a knob on 00:08:27.17900:08:27.189 it you can't have a Silla Scopes without 00:08:28.49900:08:28.509 knobs if you to run some leads that one 00:08:30.20900:08:30.219 on to veer and went on to this are you 00:08:32.81900:08:32.829 gonna measure the voltage across your 00:08:34.56000:08:34.570 battery and going into your video 00:08:36.14900:08:36.159 transmitter now when you give this thing 00:08:38.85000:08:38.860 some hoobs 00:08:39.60000:08:39.610 open up the throttle broom and the motor 00:08:41.15900:08:41.169 starts spinning a TPS he's switching the 00:08:42.83900:08:42.849 voltages or the currents really really 00:08:44.15900:08:44.169 quickly the voltage looks normally we'd 00:08:48.42000:08:48.430 have like a 12 volts sets of three so 00:08:50.34000:08:50.350 packed 12 volts straight line so over 00:08:52.01900:08:52.029 time that voltage doesn't change when 00:08:53.37000:08:53.380 you 00:08:53.91000:08:53.920 actually start putting a whole lot of 00:08:56.48000:08:56.490 load on it and start running the motor 00:08:58.53000:08:58.540 as the voltage switches off and on you 00:09:01.05000:09:01.060 get you get a buggered felt pin let's 00:09:04.31900:09:04.329 find one that works shall we 00:09:06.59000:09:06.600 you get voltage that goes like this 00:09:10.25000:09:10.260 you see that's going up and down because 00:09:12.54000:09:12.550 every time a magnet electromagnets 00:09:15.09000:09:15.100 switched on through the ESC pulls the 00:09:16.65000:09:16.660 voltage down when it's switched off the 00:09:18.09000:09:18.100 voltage goes up next one gets switched 00:09:19.71000:09:19.720 on so it goes down up and down dumps 00:09:21.12000:09:21.130 over get Alice this wave your way for 00:09:23.16000:09:23.170 wavy lines the achar noise on the 00:09:25.68000:09:25.690 voltage right of course by the ESC and 00:09:28.19900:09:28.209 Nick feeds through into the video 00:09:29.49000:09:29.500 transmitter in the Cameron you get lines 00:09:30.81000:09:30.820 all of your picture but you can fix that 00:09:33.30000:09:33.310 to a huge degree because you take your 00:09:35.06900:09:35.079 good old friendly capacitor put it on 00:09:39.06000:09:39.070 there and what happens then well when 00:09:42.26900:09:42.279 the voltage drops temporarily here 00:09:43.94900:09:43.959 because the the battery is having extra 00:09:46.23000:09:46.240 current drawn well let's say you've got 00:09:48.87000:09:48.880 it turned on right and this charges up 00:09:50.46000:09:50.470 so this charges up to 12 volts 00:09:53.60000:09:53.610 capacitors all charged up across the 00:09:55.50000:09:55.510 battery suddenly the motor the ESC draws 00:09:57.81000:09:57.820 a lot of current to drive the motor and 00:09:59.43000:09:59.440 the battery can't provide enough current 00:10:01.05000:10:01.060 it can't on its own because could that 00:10:03.38900:10:03.399 resistance so the voltage starts to drop 00:10:05.04000:10:05.050 in the battery well this also provides 00:10:07.47000:10:07.480 current out here to meet the need so 00:10:09.66000:10:09.670 it's like a backup battery but it's a 00:10:10.98000:10:10.990 very very fast battery and it can 00:10:12.81000:10:12.820 provide very very high massive current 00:10:14.16000:10:14.170 for a very short period of time if we 00:10:15.60000:10:15.610 look at the noise that's exactly what we 00:10:17.00900:10:17.019 need because we have little dips but 00:10:18.48000:10:18.490 they're very short drops in voltage as 00:10:20.57900:10:20.589 things are switching so if the capacitor 00:10:22.92000:10:22.930 can fill in those gaps you end up with 00:10:26.50900:10:26.519 the capacitor handling all these gaps 00:10:28.74000:10:28.750 here 00:10:29.13000:10:29.140 I hope I'm good enough resolution on the 00:10:30.66000:10:30.670 cameras of it so it basically takes you 00:10:32.81900:10:32.829 back to a smooth line and all the noise 00:10:34.25900:10:34.269 disappear so this is a good way to think 00:10:36.84000:10:36.850 about this I'll show you another analogy 00:10:38.37000:10:38.380 it's a brilliant analogy I'm good at 00:10:39.90000:10:39.910 those this is how capacitor works in 00:10:42.32900:10:42.339 that situation here's a car engine 00:10:44.40000:10:44.410 there's the radiator and there's the 00:10:46.71000:10:46.720 little plastic tank that you have which 00:10:48.87000:10:48.880 takes the overflow from the radiator 00:10:50.30900:10:50.319 it's like the I don't what you call it 00:10:52.05000:10:52.060 but it's the overflow tank anyway this 00:10:53.61000:10:53.620 is the engineer at my Bugatti Veyron 00:10:55.86000:10:55.870 it's a w twin engine I think but it 00:11:00.15000:11:00.160 could be any engine water called so what 00:11:01.82900:11:01.839 happens is here when you when the system 00:11:03.05900:11:03.069 is sitting there cold everything's fine 00:11:04.88900:11:04.899 now you start up the motor the engine 00:11:06.60000:11:06.610 start the engine up it gets hot 00:11:07.76900:11:07.779 and so therefore the water in the 00:11:09.30000:11:09.310 cooling system expands expands epic zone 00:11:11.87900:11:11.889 a finite space for it to be and so what 00:11:13.37900:11:13.389 happens is it's designed so that as the 00:11:15.60000:11:15.610 water expands the excess flows through a 00:11:17.16000:11:17.170 tube into a little plastic bottles so 00:11:20.10000:11:20.110 starting off and this tube goes right 00:11:22.11000:11:22.120 down to the bottom starting off you 00:11:23.91000:11:23.920 might have this much water in the bottle 00:11:25.07900:11:25.089 once the engine is warmed up you can 00:11:26.97000:11:26.980 have this much because the water's 00:11:29.18900:11:29.199 expanded inside the cooling system right 00:11:31.41000:11:31.420 so that's fine so the excess water goes 00:11:33.48000:11:33.490 into that bottle it's like charging up 00:11:35.00900:11:35.019 our capacitor from the battery the 00:11:37.35000:11:37.360 basically the the cooling system is 00:11:39.80900:11:39.819 charged up that bottle now what happens 00:11:41.99900:11:42.009 is when you turn the motor off turn the 00:11:43.74000:11:43.750 engine off everything starts to cool 00:11:45.15000:11:45.160 down and again the water shrinks but 00:11:48.05900:11:48.069 it's in a fixed thing so what happens is 00:11:50.79000:11:50.800 as the water and the radiator and the 00:11:52.49900:11:52.509 block of the engine gets smaller it 00:11:54.68900:11:54.699 starts sucking the excess water back out 00:11:56.97000:11:56.980 of that overflow bottle into the 00:11:58.61900:11:58.629 radiator Sarah don't you end up with the 00:12:00.11900:12:00.129 radiator you know being short of water 00:12:02.06900:12:02.079 and that's what the capacitor does when 00:12:03.96000:12:03.970 the voltage from our battery drops 00:12:05.34000:12:05.350 because there's a huge load from the 00:12:06.78000:12:06.790 motor the capacitor provides the extra 00:12:10.35000:12:10.360 voltage extra power needed to fill in 00:12:13.07900:12:13.089 the gap so make sure that we never run 00:12:15.17900:12:15.189 dry it provides fills in the gaps fills 00:12:17.57900:12:17.589 in the bumps on the noise I might show 00:12:19.55900:12:19.569 you I'm trying to do an experiment on 00:12:20.61000:12:20.620 the beach if I do here it is and here we 00:12:23.61000:12:23.620 are at the bench now what I've got here 00:12:24.96000:12:24.970 let me show you what I've set up here 00:12:26.06900:12:26.079 I've got my oscilloscope and I've got a 00:12:28.79900:12:28.809 power supply over here which is doing 10 00:12:30.26900:12:30.279 volts so this signal there if I wind the 00:12:33.21000:12:33.220 voltage up and down you'll see that line 00:12:35.42900:12:35.439 goes up and down that is our DC and if I 00:12:38.67000:12:38.680 turn this off completely you'll see it 00:12:41.79000:12:41.800 goes right down to the bottom once the 00:12:43.49900:12:43.509 voltage has ballooned away there we go 00:12:45.60000:12:45.610 so that's zero volts that's 10 volts 00:12:49.13900:12:49.149 right 19.8 to the map doesn't matter but 00:12:51.26900:12:51.279 that's the DC that's our battery let's 00:12:53.00900:12:53.019 say our battery is putting this voltage 00:12:54.29900:12:54.309 out now suddenly our motor starts going 00:12:58.23000:12:58.240 so it's starting to draw all sorts of 00:13:00.35000:13:00.360 current from the battery so we'll get 00:13:02.30900:13:02.319 and I'll turn this on you'll see what 00:13:03.50900:13:03.519 happens in a moment now I've got to sit 00:13:07.49900:13:07.509 it hang on let's go over I'll shall sit 00:13:09.24000:13:09.250 up the here we go here is the noise that 00:13:14.10000:13:14.110 appears on the top of our DC so it still 00:13:18.32900:13:18.339 it's not AC because zero volts is down 00:13:19.98000:13:19.990 here so it's just a noise 00:13:21.18000:13:21.190 on top of the DC this is the noise 00:13:22.77000:13:22.780 generated we've simulated it that ESC 00:13:25.41000:13:25.420 would generate and that would make lines 00:13:26.76000:13:26.770 all over a fpv gear make it look really 00:13:28.71000:13:28.720 crap so how do we fix it how do we fix 00:13:31.17000:13:31.180 it well duh 00:13:33.03000:13:33.040 mr. capacitor mr. capacitor comes to the 00:13:35.64000:13:35.650 party I'm going to put this capacitor 00:13:37.32000:13:37.330 across the battery and let's see what it 00:13:40.17000:13:40.180 does to that noise component up there so 00:13:43.17000:13:43.180 put it on here and on there look it's 00:13:47.30000:13:47.310 effectively almost removed it take it 00:13:49.38000:13:49.390 off put the capacitor but the capacitor 00:13:51.45000:13:51.460 on noise goes away take capacitor off 00:13:54.60000:13:54.610 noise comes back so this is effectively 00:13:56.37000:13:56.380 filling in the highs and lows by 00:13:59.12000:13:59.130 absorbing the high electricity and 00:14:01.55000:14:01.560 feeding it back out when the voltage 00:14:04.08000:14:04.090 drops down so that's how we remove noise 00:14:06.03000:14:06.040 using a capacitor and you've seen it 00:14:08.19000:14:08.200 yourself it must be true it was on the 00:14:10.23000:14:10.240 oscilloscope 00:14:11.01000:14:11.020 now here's another really cool thing 00:14:12.21000:14:12.220 about capacitors in another place that 00:14:13.65000:14:13.660 used very often and that is separating 00:14:16.08000:14:16.090 AC from DC now DC's direct current 00:14:18.96000:14:18.970 that's just like a battery and the Vox 00:14:20.13000:14:20.140 just current one voltage and it just 00:14:21.75000:14:21.760 goes round the circle or wherever 00:14:22.71000:14:22.720 through the circuitry it's just a direct 00:14:24.42000:14:24.430 current doesn't it doesn't change 00:14:26.52000:14:26.530 polarity stays the same polarity 00:14:27.87000:14:27.880 alternating current however it goes 00:14:29.82000:14:29.830 because of course we have AC in our 00:14:31.65000:14:31.660 houses if you're in America you've got a 00:14:33.06000:14:33.070 hundred and ten volts AC if you're in 00:14:34.89000:14:34.900 Europe and Australia and New Zealand you 00:14:37.05000:14:37.060 pay more so you get two hundred and 00:14:38.76000:14:38.770 twenty volts ac and that means that the 00:14:41.16000:14:41.170 voltage just changes up and down what 00:14:43.02000:14:43.030 I've drawn here is a picture of this 00:14:44.61000:14:44.620 quite normal here's say 12 volts and 00:14:46.68000:14:46.690 we've got a wiggly line so this 00:14:49.02000:14:49.030 particular this is their oscilloscope of 00:14:50.91000:14:50.920 course this is voltage this is time so 00:14:52.59000:14:52.600 on this signal here we've got an AC 00:14:54.30000:14:54.310 waveform superimposed on a DC voltage 00:14:57.18000:14:57.190 because the actual voltage never goes 00:14:59.46000:14:59.470 below zero but it does go up and down so 00:15:02.85000:15:02.860 you might say we only want the AC 00:15:04.64000:15:04.650 component let's say we're coupling a 00:15:06.63000:15:06.640 video camera to a video transmitter 00:15:09.80000:15:09.810 somewhere in there you might find that 00:15:12.32900:15:12.339 you want to change it from being like 00:15:14.46000:15:14.470 this - just being pure AC that's what 00:15:17.28000:15:17.290 you do is you do this if we put this is 00:15:19.26000:15:19.270 the waveform that we'd see here so it's 00:15:22.41000:15:22.420 got DC coming Edea there's 12 volts on 00:15:24.27000:15:24.280 here and it's got that signal on the top 00:15:26.64000:15:26.650 you just want the AC out here you put a 00:15:29.01000:15:29.020 capacitor in there if we drew this graph 00:15:30.21000:15:30.220 again 12 volts zero 00:15:34.74000:15:34.750 then what you'd get is this 00:15:39.26000:15:39.270 you've still got that wiggly line but 00:15:41.82000:15:41.830 it's down at zero volts it's taking out 00:15:43.35000:15:43.360 the DC because capacitors block DC 00:15:45.99000:15:46.000 competitors do not allow direct current 00:15:47.46000:15:47.470 to flow I'll show you with the meter on 00:15:48.66000:15:48.670 the bench if we put a meter on or put a 00:15:51.45000:15:51.460 capacitor in the circuit nothing happens 00:15:53.52000:15:53.530 no current flows if it's DC nothing 00:15:55.20000:15:55.210 happens at all because the DC can't 00:15:56.88000:15:56.890 travel because remember capacitor has 00:15:58.41000:15:58.420 two plates with an inch later in between 00:16:00.33000:16:00.340 so the current can flow through the 00:16:01.62000:16:01.630 insulator simple as that 00:16:03.54000:16:03.550 this how we can extract a AC signal from 00:16:06.15000:16:06.160 a situation where it has a DC component 00:16:08.40000:16:08.410 and getting a bit complex here but 00:16:10.26000:16:10.270 basically that happens a lot in signal 00:16:12.45000:16:12.460 processing receivers and audio 00:16:14.67000:16:14.680 amplifiers stuff like that video stuff 00:16:16.68000:16:16.690 we need to you know I select those two 00:16:18.15000:16:18.160 components so let's take a look at the 00:16:19.62000:16:19.630 different types of capacitors the way 00:16:21.39000:16:21.400 they are made 00:16:22.05000:16:22.060 and as they basically all of them are 00:16:24.81000:16:24.820 two plates with an insulator in between 00:16:26.64000:16:26.650 but the way to physically weigh their 00:16:28.11000:16:28.120 work the way they're physically made 00:16:29.16000:16:29.170 vary significantly and a size and 00:16:31.32000:16:31.330 everything vary significantly because if 00:16:32.76000:16:32.770 obviously if you've got a capacitor 00:16:34.53000:16:34.540 that's designed to handle very high 00:16:35.73000:16:35.740 voltages the insulator must be quite 00:16:37.71000:16:37.720 thick and therefore it's going to be a 00:16:39.75000:16:39.760 bulkier capacitor if you only have to 00:16:41.34000:16:41.350 deal with like six volts you can make 00:16:42.69000:16:42.700 things later so super super thin that 00:16:44.82000:16:44.830 you can make the capacitor really really 00:16:46.38000:16:46.390 small so there are a number of the most 00:16:48.36000:16:48.370 common capacitors we use in the Hobby 00:16:50.91000:16:50.920 today or the manufacturers use are what 00:16:52.95000:16:52.960 we call ceramic ceramic capacitors their 00:16:56.94000:16:56.950 little square block things they mount 00:16:58.23000:16:58.240 the surface mount components they fit on 00:16:59.85000:16:59.860 a circuit board I'll put a picture of 00:17:01.86000:17:01.870 one up here hopefully and it just looks 00:17:04.53000:17:04.540 like a little rectangle little block 00:17:06.63000:17:06.640 with little silver ends and but if we 00:17:08.76000:17:08.770 were to look at it cross section it so 00:17:10.86000:17:10.870 here's our ceramic capacitor as a silver 00:17:13.71000:17:13.720 in there and a silver in there and it 00:17:15.60000:17:15.610 goes onto a circuit board normally the 00:17:18.36000:17:18.370 circuit board is like that and you'll 00:17:20.01000:17:20.020 see the solder there and solder there 00:17:21.51000:17:21.520 they said they fit now inside here very 00:17:23.67000:17:23.680 very clever what they've got is from 00:17:26.73000:17:26.740 each end there are little plates come 00:17:31.77000:17:31.780 out like this and they like they go like 00:17:34.95000:17:34.960 fingers and link up together so like 00:17:37.77000:17:37.780 this if you imagine yeah like that and 00:17:40.23000:17:40.240 so therefore you can see the whole plate 00:17:42.63000:17:42.640 thing you've got a plate you're going to 00:17:43.65000:17:43.660 inch later plate and chelate a plate 00:17:45.12000:17:45.130 inch later so because they are dealing 00:17:47.66900:17:47.679 with you the fairly low 00:17:48.72000:17:48.730 voltages generally less than 25 volts 00:17:50.66900:17:50.679 the the insulator the ceramic that 00:17:52.74000:17:52.750 insulates has met those plates is very 00:17:54.69000:17:54.700 very very thin and that means the whole 00:17:57.21000:17:57.220 capacitor can be really small another 00:17:59.46000:17:59.470 benefit is it'll work either way around 00:18:00.99000:18:01.000 you you can dust matter with your 00:18:02.25000:18:02.260 positive on this end and negative on 00:18:04.16900:18:04.179 there or whether you do the reverse and 00:18:05.70000:18:05.710 have negative on there and positive on 00:18:06.99000:18:07.000 there they don't care about polarity 00:18:08.61000:18:08.620 they're just independent and so these 00:18:10.74000:18:10.750 are very common very popular they're 00:18:12.06000:18:12.070 quite quite tough but they can be broken 00:18:14.01000:18:14.020 with sudden shock because ceramic is a 00:18:16.08000:18:16.090 bit brittle sometimes so but they are 00:18:18.53900:18:18.549 that the the backbone of modern 00:18:21.33000:18:21.340 electronics and you get them from from a 00:18:23.03900:18:23.049 few hundred Pico farad's up to several 00:18:26.58000:18:26.590 micro farad's so they cover a wide range 00:18:29.07000:18:29.080 and generally the more farad more micro 00:18:30.87000:18:30.880 farad's you've got the bigger they are 00:18:31.91900:18:31.929 so some of quite big some are quite 00:18:33.29900:18:33.309 small that's ceramic so they're just a 00:18:36.60000:18:36.610 component you'll find on a circuit board 00:18:37.86000:18:37.870 now the other type that you'll find very 00:18:40.86000:18:40.870 very commonly there's something called 00:18:42.63000:18:42.640 an electrolytic and I'll draw a picture 00:18:44.03900:18:44.049 of one here well I'm very crappy at 00:18:50.28000:18:50.290 drawing and they just got like a little 00:18:56.19000:18:56.200 cairn I got two wire legs in at the 00:18:57.69000:18:57.700 bottom that's the normal it's what they 00:18:59.49000:18:59.500 call a through-hole version and they're 00:19:02.10000:19:02.110 very interesting because they're 00:19:03.24000:19:03.250 different to ceramic they're dumb to 00:19:05.13000:19:05.140 ceramic because first of all they have a 00:19:06.87000:19:06.880 polarity you can only use them one way 00:19:09.00000:19:09.010 around if you put an around the other 00:19:11.07000:19:11.080 way 00:19:11.28000:19:11.290 bad things happen but electronics are 00:19:14.40000:19:14.410 very cheap to make and they can have 00:19:16.56000:19:16.570 quite high capacities so that's why you 00:19:18.75000:19:18.760 commonly find them when you're looking 00:19:20.43000:19:20.440 at values of plus a hundred fifty micro 00:19:22.74000:19:22.750 farad's will beget generally you'll find 00:19:24.18000:19:24.190 an electrolytic capacitor and the way 00:19:25.86000:19:25.870 they're built is stunningly clever if 00:19:27.78000:19:27.790 you were to look inside here you'll find 00:19:30.06000:19:30.070 that mr. Stuart cross-section from the 00:19:33.81000:19:33.820 top here's the can if we took cut the 00:19:37.26000:19:37.270 coat of top off the can you would find 00:19:39.03000:19:39.040 that there was a spiral of metal foil 00:19:44.01000:19:44.020 like that and another spiral of metal 00:19:47.25000:19:47.260 foil like that if I can get it right so 00:19:52.50000:19:52.510 so there's two layers of metal foil 00:19:54.21000:19:54.220 there round into a spiral and then there 00:19:58.20000:19:58.210 is a liquid in there was liquid what's 00:20:01.32000:20:01.330 the liquid for the liquid 00:20:02.52000:20:02.530 is part of the whole construction and 00:20:04.05000:20:04.060 we'll show you in a simplified form how 00:20:07.23000:20:07.240 this all works right here is one plate 00:20:10.50000:20:10.510 of our electrolytic capacitor part of 00:20:14.01000:20:14.020 that spiral and here is the other one 00:20:17.21000:20:17.220 because these go off this will go off to 00:20:19.41000:20:19.420 my plus and this will go off to - and 00:20:24.92000:20:24.930 obviously you've got the can in there so 00:20:26.97000:20:26.980 we just assume that this is a thing and 00:20:28.56000:20:28.570 there is a liquid in here so what 00:20:31.32000:20:31.330 happens is these are aluminium usually 00:20:32.91000:20:32.920 aluminium there can be other embezzles 00:20:35.07000:20:35.080 but aluminium is the most common you can 00:20:36.39000:20:36.400 have tantalum and nothing there's no VM 00:20:37.83000:20:37.840 as well but Elementium electronics are 00:20:40.05000:20:40.060 most common and what happens is when a 00:20:42.78000:20:42.790 current is passed a forming current is 00:20:44.46000:20:44.470 passed through this capacitor you get 00:20:46.59000:20:46.600 anodizing takes place anodizing is a 00:20:48.36000:20:48.370 really cool thing too it converts 00:20:49.47000:20:49.480 aluminium into aluminium oxide and 00:20:51.93000:20:51.940 aluminium conducts electricity really 00:20:53.91000:20:53.920 well 00:20:54.27000:20:54.280 aluminum oxide doesn't conduct it also 00:20:57.03000:20:57.040 when you do this if you pass a current 00:20:58.80000:20:58.810 through here a very very very very thin 00:21:02.52000:21:02.530 layer of oxide different coloured pin 00:21:04.92000:21:04.930 yeah see if this one a week very very 00:21:07.32000:21:07.330 different thin layer of oxide as thin as 00:21:09.75000:21:09.760 my pin here forms around this electrode 00:21:13.85000:21:13.860 and it becomes in this you later 00:21:16.31000:21:16.320 suddenly the electricity can't flow 00:21:19.53000:21:19.540 anymore 00:21:20.04000:21:20.050 and of course it's a perfect capacitor 00:21:21.81000:21:21.820 because the capacitance of a capacitor 00:21:24.24000:21:24.250 is determined by two things the area of 00:21:27.12000:21:27.130 those plates and how close they are 00:21:28.74000:21:28.750 together so the bigger the plates the 00:21:30.60000:21:30.610 more capacity and the closer you can get 00:21:32.16000:21:32.170 them together without them touching an 00:21:33.81000:21:33.820 electricity flowing then the higher the 00:21:35.52000:21:35.530 capacity you get so what they do here is 00:21:37.95000:21:37.960 by using a oxide it's only a few atoms 00:21:40.92000:21:40.930 thick few molecules thick on the surface 00:21:43.26000:21:43.270 of the thing and also remember because 00:21:45.69000:21:45.700 this electrolyte here is a conductor 00:21:48.27000:21:48.280 conducts electricity effectively you've 00:21:50.22000:21:50.230 got the the negative within a few atoms 00:21:52.83000:21:52.840 of the positive plate and so you get 00:21:55.23000:21:55.240 massive massive amounts of capacity in a 00:21:57.60000:21:57.610 really small space so that's why we use 00:22:00.18000:22:00.190 electronics and enables us to make 00:22:01.65000:22:01.660 really really high capacity capacitors 00:22:03.69000:22:03.700 in a fairly small space that's the 00:22:06.54000:22:06.550 secret 00:22:07.08000:22:07.090 so they are very very common where you 00:22:08.73000:22:08.740 need a lot of capacity now obviously 00:22:10.89000:22:10.900 because that's such a very thin film of 00:22:12.78000:22:12.790 oxide the voltage rating is very very 00:22:15.12000:22:15.130 critical 00:22:15.88000:22:15.890 exceed the voltage rating then that film 00:22:17.53000:22:17.540 will break down and bad things will 00:22:19.24000:22:19.250 happen because effectively you've 00:22:20.17000:22:20.180 shorted out your capacitor because the 00:22:22.27000:22:22.280 electrolyte will still have the negative 00:22:23.44000:22:23.450 and this will be positive with nothing 00:22:25.24000:22:25.250 separating them so the current will flow 00:22:26.59000:22:26.600 and boom because these things go bang - 00:22:29.83000:22:29.840 I trust me if you get if you get a 00:22:32.62000:22:32.630 failure inside electrolytic capacitor 00:22:34.06000:22:34.070 they explode and for that reason if you 00:22:36.52000:22:36.530 look at the top on try and overlay a 00:22:38.35000:22:38.360 picture this is the top again you'll 00:22:41.05000:22:41.060 find that there's some little grooves 00:22:42.16000:22:42.170 little things cut on the top of the can 00:22:43.66000:22:43.670 that's because it provides safe venting 00:22:46.72000:22:46.730 if something does go wrong and this 00:22:47.98000:22:47.990 shorts out and this liquid this 00:22:50.08000:22:50.090 electrolyte starts boiling because of 00:22:51.61000:22:51.620 all the electrical energy flowing 00:22:53.23000:22:53.240 through it then these little grooves 00:22:55.90000:22:55.910 they will split on the top of the camel 00:22:57.49000:22:57.500 open up rather than the whole thing 00:22:58.30000:22:58.310 exploding and creating your danger 00:22:59.80000:22:59.810 that's the theory it'll just split you 00:23:01.72000:23:01.730 can often tell if an electrolytic 00:23:02.77000:23:02.780 capacitor is faulty because instead of 00:23:04.54000:23:04.550 having a perfectly flat top let me show 00:23:07.03000:23:07.040 you what you know so like this instead 00:23:11.05000:23:11.060 of having a perfectly flat top they dome 00:23:12.88000:23:12.890 up they start doming up because what's 00:23:14.50000:23:14.510 happened is that the liquid in here has 00:23:16.36000:23:16.370 turned - guess that's pressurized it and 00:23:18.43000:23:18.440 if you see that there capacitors bugger 00:23:20.41000:23:20.420 - even if it's working now to be stuffed 00:23:22.06000:23:22.070 in a very short period of time so you 00:23:23.41000:23:23.420 replace it so electrolytic capacitors 00:23:26.59000:23:26.600 they are fantastic but they do have a 00:23:28.60000:23:28.610 finite lifetime because where the wires 00:23:31.78000:23:31.790 come in there's usually a rubber seal 00:23:33.13000:23:33.140 down here and and stuff gets past the 00:23:36.25000:23:36.260 rubber seals and over time the electron 00:23:37.87000:23:37.880 the electrolyte gets breaks down and 00:23:40.60000:23:40.610 gets contaminated and so they don't last 00:23:42.73000:23:42.740 forever they're not like the ceramic 00:23:44.74000:23:44.750 cats which in theory will last forever 00:23:46.48000:23:46.490 electrolytic not so good and there is 00:23:49.18000:23:49.190 another form electrolytic capacitor 00:23:50.29000:23:50.300 called a tantalum which is quite common 00:23:52.33000:23:52.340 in our little stuff it's usually a 00:23:53.92000:23:53.930 little orange rectangle and I'll show 00:23:56.68000:23:56.690 you some of those on the bench and they 00:23:59.38000:23:59.390 are also very high capacity for a very 00:24:01.09000:24:01.100 small space in fact higher capacity than 00:24:02.53000:24:02.540 the aluminum ones because the tantalum 00:24:04.30000:24:04.310 oxide film is even thinner than the 00:24:06.31000:24:06.320 aluminium oxide film but they also are 00:24:09.04000:24:09.050 very prone to failure put too much 00:24:10.27000:24:10.280 voltage on them they turn black and 00:24:11.89000:24:11.900 smoke and flames come roaring out whew 00:24:13.81000:24:13.820 great fun and you might notice that if 00:24:15.97000:24:15.980 you've ever connected a battery around 00:24:17.41000:24:17.420 the wrong way to a receiver 00:24:18.61000:24:18.620 probably the smoke was caused by the 00:24:20.80000:24:20.810 tantalum capacitors that are sitting 00:24:22.36000:24:22.370 across the battery input to smooth out 00:24:24.46000:24:24.470 the noise that might come from your ESC 00:24:26.35000:24:26.360 or error as we mentioned earlier is 00:24:28.87000:24:28.880 simple now there is another type of 00:24:30.76000:24:30.770 capacitor called plastic film capacitors 00:24:32.35000:24:32.360 sometimes called a mylar capacitor 00:24:34.30000:24:34.310 sometimes called a polyester capacitor 00:24:35.80000:24:35.810 that's describing the type of plastic 00:24:37.39000:24:37.400 film that separates the place I've drawn 00:24:38.77000:24:38.780 the thing yeah I mean here we go 00:24:40.27000:24:40.280 there's one plate usually that's a foil 00:24:41.98000:24:41.990 it's kind of a usually an aluminium foil 00:24:43.87000:24:43.880 so you get a foil plate in a foil plate 00:24:46.18000:24:46.190 in a plastic sheet separating them and 00:24:47.95000:24:47.960 then they wind them all up screw them up 00:24:49.21000:24:49.220 into a little ball and then they're 00:24:51.07000:24:51.080 small enough to use on a circuit board 00:24:52.15000:24:52.160 I've actually made one I made one myself 00:24:54.22000:24:54.230 out of kitchen foil and kitchen film and 00:24:56.76000:24:56.770 let's go to the bench and I'll show you 00:24:58.69000:24:58.700 will measured it has capacity I'll show 00:25:00.40000:25:00.410 you another really interesting thing 00:25:02.50000:25:02.510 associated with these capacitors and how 00:25:05.41000:25:05.420 it goes back to the video I did last 00:25:06.79000:25:06.800 week about MEMS devices let's go to the 00:25:09.10000:25:09.110 bench and look at there now and here is 00:25:10.99000:25:11.000 my homemade capacitor I promised you 00:25:12.46000:25:12.470 here we go look what I've got here is 00:25:13.96000:25:13.970 two by two sheets of aluminium foil or 00:25:16.93000:25:16.940 aluminum foil if you live in the USA 00:25:18.46000:25:18.470 just kitchen foil and some plastic which 00:25:22.00000:25:22.010 is separating those sheets so we have 00:25:25.03000:25:25.040 two plates and an insulator the 00:25:26.74000:25:26.750 insulator is just as kitchen film this 00:25:28.15000:25:28.160 cling film separating the two sheets and 00:25:30.91000:25:30.920 yeah I've got my multimeter and most 00:25:32.65000:25:32.660 reasonable multimeters have a 00:25:34.62000:25:34.630 capacitance case it's that little 00:25:37.48000:25:37.490 capacitor symbol so you know that sort 00:25:38.89000:25:38.900 of us and it's going to there and we'll 00:25:40.72000:25:40.730 measure my capacitor right now because 00:25:43.18000:25:43.190 we've got wires close to get them got a 00:25:44.74000:25:44.750 capacitor there's what we call residual 00:25:46.81000:25:46.820 parasitic capacitance and this we need 00:25:48.37000:25:48.380 to get rid of that I press this button 00:25:49.60000:25:49.610 here and it will zero will it come on 00:25:53.02000:25:53.030 they regard didn't press it hard enough 00:25:54.22000:25:54.230 zero so now I'm going to measure my 00:25:55.87000:25:55.880 capacitor by putting one probe on there 00:25:58.24000:25:58.250 and one probe on there and it should 00:26:00.01000:26:00.020 tell me that whoa we've got 17 nano 00:26:02.92000:26:02.930 farad's in our capacitor there you go so 00:26:05.50000:26:05.510 that's a 17 nano farad capacitor there 00:26:07.30000:26:07.310 not a very good one but it's there now 00:26:09.55000:26:09.560 I'm gonna show you something else 00:26:10.33000:26:10.340 remember last week I talked about the 00:26:11.62000:26:11.630 MEMS devices and how they used like they 00:26:14.65000:26:14.660 had a capacitor on there which varied in 00:26:16.21000:26:16.220 value because the plates came closer and 00:26:18.13000:26:18.140 further apart due to the Coriolis effect 00:26:20.80000:26:20.810 now I'm going to show you how that works 00:26:22.87000:26:22.880 so let's measure a capacitor drink it my 00:26:25.00000:26:25.010 probes on here evenly 00:26:26.89000:26:26.900 okay there we go we've got six deep 00:26:29.32000:26:29.330 roughly roughly 17 to 18 oh it's going 00:26:31.81000:26:31.820 up a bit cuz I'm pressing hard I won't 00:26:33.01000:26:33.020 press so hard here seventeen 00:26:35.86000:26:35.870 nano farad you watch what happens when I 00:26:37.48000:26:37.490 press on my capacitor whoa 00:26:40.84000:26:40.850 shut up to 40 00:26:42.15900:26:42.169 3:45 time handoff goes back down to 17 00:26:45.75900:26:45.769 or 18 Chris again now why is that 00:26:49.14900:26:49.159 capacity changing well it's changing 00:26:50.61900:26:50.629 because I'm pushing the plates closer 00:26:52.09000:26:52.100 together cuz there's air between the 00:26:53.68000:26:53.690 plates now this is just it's not tightly 00:26:55.59900:26:55.609 wound so when I press the arrow and push 00:26:57.63900:26:57.649 the plates closer together it's still 00:26:59.37900:26:59.389 separated by the plastic film the D 00:27:01.29900:27:01.309 electric capacitance goes up and it's 00:27:03.15900:27:03.169 how that MEMS device works as the two 00:27:05.64900:27:05.659 parts of the MEMS device get closer 00:27:06.94000:27:06.950 together the capacity goes up and when 00:27:09.70000:27:09.710 they go further apart capacity falls 00:27:11.37900:27:11.389 down so that's how they measure it no 00:27:13.62900:27:13.639 electrical conduction or connection 00:27:15.39900:27:15.409 required it's just a capacitance thing 00:27:17.22900:27:17.239 so you could build your own capacitive 00:27:18.46000:27:18.470 touch bed that's how you roughly how 00:27:22.35900:27:22.369 your capacitive touch screen works on 00:27:23.76900:27:23.779 your cell phone - there you go isn't 00:27:25.57000:27:25.580 that simple figure and make your own 00:27:27.12900:27:27.139 capacitor yeah I'll show you something 00:27:28.86900:27:28.879 here which is gonna surprise you it's 00:27:30.39900:27:30.409 gonna shock you now that's my roughly 15 00:27:33.60900:27:33.619 or 18 nano farad capacitor but remember 00:27:37.84000:27:37.850 I took the best ceramic capacitors and 00:27:39.09900:27:39.109 how effective they are and how small 00:27:40.38900:27:40.399 let's have a look here's a 15 nano farad 00:27:42.90900:27:42.919 let me just pull in a bit so you can see 00:27:44.40900:27:44.419 okay 00:27:45.36900:27:45.379 there they are here's my finger as a 00:27:47.44000:27:47.450 size comparison here are the meter 00:27:49.35900:27:49.369 probes as a size comparison that has got 00:27:52.38900:27:52.399 the same those little each one of those 00:27:54.00900:27:54.019 individual components is the same 00:27:55.23900:27:55.249 capacity as my honking great handmade 17 00:28:01.14900:28:01.159 or 18 nano farad capacitor here so you 00:28:04.11900:28:04.129 can see that how do they get so much 00:28:06.07000:28:06.080 capacity in a small device well 00:28:07.26900:28:07.279 obviously the plates much smaller than 00:28:10.29900:28:10.309 these plates but there's so much closer 00:28:12.03900:28:12.049 together that you get a high capacity of 00:28:15.34000:28:15.350 matching capacity so if I put this in a 00:28:17.59000:28:17.600 vise and scrunched it really tightly I'd 00:28:19.35900:28:19.369 probably get I may even get a couple of 00:28:21.48900:28:21.499 hundred nano ferret's of capacity out of 00:28:23.73900:28:23.749 that homemade capacitor but by doing it 00:28:25.96000:28:25.970 with a ceramic substrate very very thin 00:28:27.58000:28:27.590 very very small spacings they can give 00:28:29.25900:28:29.269 that of a tiny tiny little device like 00:28:31.26900:28:31.279 that and finally another place we use 00:28:33.97000:28:33.980 resistors sometimes is in determining 00:28:36.46000:28:36.470 timings oscillators and things because 00:28:38.91900:28:38.929 one of the interesting things about a 00:28:40.57000:28:40.580 capacitor is that as I mentioned they 00:28:43.09000:28:43.100 will charge really quickly but if you 00:28:44.56000:28:44.570 put a resistor in series with the 00:28:45.87900:28:45.889 capacitor 00:28:46.33000:28:46.340 it'll limit the rate at which it charges 00:28:48.00900:28:48.019 because obviously the the current is 00:28:49.47900:28:49.489 reduced by having to pass through a 00:28:51.39900:28:51.409 resistor so instead of just charging it 00:28:53.16900:28:53.179 up instantly it takes a while to charge 00:28:55.47900:28:55.489 up and that 00:28:56.16900:28:56.179 I'm it takes is something called the RC 00:28:59.10900:28:59.119 constant or the RCS or resistance times 00:29:01.60000:29:01.610 the capacitance and that enables us to 00:29:03.34000:29:03.350 do things like calculating build 00:29:05.23000:29:05.240 circuits that will trigger a certain 00:29:08.68000:29:08.690 thing to happen at a certain time now if 00:29:10.21000:29:10.220 we look at here's our oscilloscope 00:29:11.73900:29:11.749 connect it across that capacitor with 00:29:13.50900:29:13.519 the resistance in there 00:29:14.44000:29:14.450 what happens is we get something that 00:29:16.06000:29:16.070 looks like this as you can see it takes 00:29:20.20000:29:20.210 time as they slowly the capacitor 00:29:22.65900:29:22.669 charged up this is the voltage this is 00:29:24.97000:29:24.980 time so the capacitor doesn't just 00:29:26.79900:29:26.809 suddenly charge right up it takes time 00:29:28.14900:29:28.159 to charge up so if you have something 00:29:29.35000:29:29.360 here let's say we have a threshold here 00:29:31.33000:29:31.340 at this point here if we decide that 00:29:33.22000:29:33.230 that's going to turn on a transistor or 00:29:34.62900:29:34.639 something then that's the time that it 00:29:37.38900:29:37.399 takes to do it if we double the 00:29:38.71000:29:38.720 capacitance or if we have the 00:29:40.21000:29:40.220 capacitance then obviously that would 00:29:42.03900:29:42.049 charge more quickly and the thing would 00:29:44.61900:29:44.629 go there if we change the resistance 00:29:45.70000:29:45.710 value so we can use a combination of 00:29:47.16900:29:47.179 capacitors and resistors to develop time 00:29:49.77900:29:49.789 periods and use those time periods to 00:29:51.36900:29:51.379 switch stuff off and on not so common 00:29:53.10900:29:53.119 these days in the world of digital but 00:29:55.29900:29:55.309 back in the analog days it was a very 00:29:56.61900:29:56.629 very common way to create a timer or 00:29:58.84000:29:58.850 something like that just charge 00:29:59.76900:29:59.779 capacitor and wait till it gets to a 00:30:00.87900:30:00.889 certain voltage when it hits that 00:30:02.20000:30:02.210 voltage something happens Bing and you 00:30:03.82000:30:03.830 can vary this resistance if you make 00:30:05.20000:30:05.210 this a variable resistor you can then 00:30:07.93000:30:07.940 tweak a knob to change the time frame 00:30:10.62900:30:10.639 darkroom timers a lot of people to make 00:30:12.19000:30:12.200 darkroom time is way back in the old 00:30:13.57000:30:13.580 days as simple as that 00:30:14.79900:30:14.809 you know when you used to use film and 00:30:16.21000:30:16.220 cameras you need to have a certain 00:30:17.20000:30:17.210 amount of time before you took there the 00:30:18.85000:30:18.860 film at or the exposure out of this tank 00:30:21.73000:30:21.740 and put another one same thing there you 00:30:23.61900:30:23.629 just tweak a little knob and it would 00:30:25.02900:30:25.039 take a certain amount of time to charge 00:30:26.13900:30:26.149 the capacitor okay that's quite simple 00:30:28.65900:30:28.669 yeah that's capacitors basically one 00:30:33.43000:30:33.440 application the final application that 00:30:35.08000:30:35.090 you'll find for these things is in the 00:30:37.21000:30:37.220 hobby is as an alternative to a battery 00:30:39.85000:30:39.860 now if you go out shopping for Christmas 00:30:41.64900:30:41.659 presents as you you'll probably find 00:30:42.78900:30:42.799 little airplanes electric planes that 00:30:44.73900:30:44.749 you can charge up they take 20 seconds 00:30:46.50900:30:46.519 to charge or you know listen a minute to 00:30:48.34000:30:48.350 charge may fly for 20 seconds or so and 00:30:50.08000:30:50.090 a lot of people I saw talking to guide 00:30:51.99900:30:52.009 the other day who said you they must 00:30:53.37900:30:53.389 have a good battery and them I said no 00:30:54.58000:30:54.590 they've actually got a capacitor they've 00:30:55.74900:30:55.759 got a super cap in them 00:30:57.12900:30:57.139 it's a capacitor with so much capacity 00:30:59.15900:30:59.169 that it will hold enough power to drive 00:31:02.20000:31:02.210 the little tiny motor for 20 seconds you 00:31:04.41900:31:04.429 know and that's a lot of power 00:31:06.58000:31:06.590 you know going back a few years we do 00:31:09.15900:31:09.169 have super caps you have to you 00:31:10.16900:31:10.179 battery but that's an example of using a 00:31:11.99900:31:12.009 capacitor in place of a battery another 00:31:13.68000:31:13.690 example of that is a growing number of 00:31:16.40900:31:16.419 electronic devices which have memory 00:31:18.53900:31:18.549 that must be kept active when you change 00:31:20.54900:31:20.559 the batteries or something they used to 00:31:21.65900:31:21.669 use a little coin cell and the little 00:31:23.36900:31:23.379 coin cells only last three years after 00:31:25.01900:31:25.029 three years when you went to change the 00:31:26.31000:31:26.320 batteries all the memory was forgotten 00:31:27.57000:31:27.580 and sometimes it was just a good example 00:31:30.18000:31:30.190 as prep see all junior radio is they had 00:31:31.85900:31:31.869 a battery to back up the the model 00:31:34.91900:31:34.929 memory in the old jr. nine 303's and 00:31:37.37900:31:37.389 things like that nice we have to 00:31:38.27900:31:38.289 configure anyway those old radios had a 00:31:40.88900:31:40.899 coin cell on them and after five years 00:31:42.18000:31:42.190 the coin cell battery would often go 00:31:43.44000:31:43.450 flat and then when you if you did the 00:31:45.72000:31:45.730 radio go flat you'd get a error and you 00:31:47.87900:31:47.889 have to take it to the dealer and you 00:31:49.16900:31:49.179 have to fix it because you couldn't fix 00:31:50.39900:31:50.409 it yourself but that sort of thing these 00:31:52.56000:31:52.570 days has they instead of using coin 00:31:55.20000:31:55.210 cells they often use super caps which 00:31:57.06000:31:57.070 will keep something alive long enough to 00:31:59.84000:31:59.850 enable you to change your battery or 00:32:01.76900:32:01.779 something even some GPS receivers now 00:32:03.45000:32:03.460 have super caps so that if you're using 00:32:05.87900:32:05.889 it turning it off around during the day 00:32:07.23000:32:07.240 you will remember it's Almanac from one 00:32:10.28900:32:10.299 operation to another some of them still 00:32:12.45000:32:12.460 use a little tiny lithium battery but a 00:32:14.54900:32:14.559 lot of them are switching to super caps 00:32:15.89900:32:15.909 because lithium batteries don't last 00:32:17.54900:32:17.559 forever 00:32:18.14900:32:18.159 super caps virtually do so it's just 00:32:20.78900:32:20.799 another use for capacitors in the hobby 00:32:23.99900:32:24.009 so let's see if we can identify some of 00:32:26.22000:32:26.230 these capacitor types on common parts of 00:32:28.91900:32:28.929 the Hobby common components this is a 00:32:30.45000:32:30.460 flight controller board and these little 00:32:32.60900:32:32.619 orange things here and here and there 00:32:34.73900:32:34.749 and there that tantalum capacitors 00:32:36.53900:32:36.549 they're a type of electronic they use 00:32:37.95000:32:37.960 the tantalum metal instead of aluminium 00:32:40.01900:32:40.029 and a tantalum oxide and I think there's 00:32:42.14900:32:42.159 some on the other side as well and these 00:32:43.68000:32:43.690 ones here are obviously used as 00:32:44.84000:32:44.850 smoothing capacitors there's reservoirs 00:32:47.03900:32:47.049 of capacitors as we've talked about with 00:32:49.10900:32:49.119 the in the demonstration we did with the 00:32:51.29900:32:51.309 oscilloscope so those are tantalum 00:32:54.02900:32:54.039 I don't there's a couple of ceramics but 00:32:56.48900:32:56.499 I'd say yeah there's a couple of 00:32:57.41900:32:57.429 ceramics I think and there's a templum 00:33:00.14900:33:00.159 tantalum is used because it's got a lot 00:33:02.03900:33:02.049 more capacity than the ceramic and the 00:33:04.10900:33:04.119 ceramic is used because ceramics 00:33:05.85000:33:05.860 actually have a lower ESR that they they 00:33:07.91900:33:07.929 can they work better at high frequencies 00:33:09.96000:33:09.970 ceramics we good at high frequencies so 00:33:11.85000:33:11.860 we've got a power regulator I like this 00:33:13.28900:33:13.299 is a pair regulator you have some 00:33:15.02900:33:15.039 tantalum switch fill in the big gap so 00:33:17.27900:33:17.289 the low frequency noise is handled by 00:33:20.19000:33:20.200 the tantalum but the very high frequency 00:33:21.93000:33:21.940 noise these don't absorb it very 00:33:23.91000:33:23.920 well so they used the ceramics which 00:33:25.53000:33:25.540 handle high frequencies really well so 00:33:27.48000:33:27.490 you not only get rid of any 00:33:28.56000:33:28.570 low-frequency noise but also 00:33:29.64000:33:29.650 high-frequency noise so these will be in 00:33:31.29000:33:31.300 parallel across that to get the best of 00:33:33.12000:33:33.130 both worlds so to speak and here's a 00:33:34.89000:33:34.900 foreign one he is seeing on this we can 00:33:36.66000:33:36.670 see a range of various ceramic 00:33:38.79000:33:38.800 capacitors but these ones down here 00:33:39.84000:33:39.850 obviously you can see these are probably 00:33:41.01000:33:41.020 all in parallel to provide extra 00:33:42.72000:33:42.730 capacity because if you put too 10 micro 00:33:45.45000:33:45.460 farad capacitors in parallel you get 20 00:33:47.28000:33:47.290 micro farad's they just double up it's 00:33:48.99000:33:49.000 like when you put batteries in in 00:33:50.55000:33:50.560 parallel you increase the current 00:33:52.14000:33:52.150 capacity will increase the capacity of a 00:33:54.21000:33:54.220 capacitor when you parallel it up with 00:33:55.95000:33:55.960 one of the same size so yeah that's 00:33:58.34000:33:58.350 sometimes es C's have a lot of 00:34:01.05000:34:01.060 capacitors to smooth out the noise 00:34:02.34000:34:02.350 especially the older one so I'll see if 00:34:03.99000:34:04.000 I can find an older style you see show 00:34:05.70000:34:05.710 you what I mean and here is a blast from 00:34:07.77000:34:07.780 the past this isn't listen to pull out a 00:34:09.75000:34:09.760 bit here on this so you can see this is 00:34:11.15900:34:11.169 marled iMix p230 with six inch arms and 00:34:15.12000:34:15.130 props and the es is used back in the old 00:34:18.27000:34:18.280 days you can see on these old 00:34:20.31000:34:20.320 what are they brand there but you can 00:34:24.27000:34:24.280 see on these old ears he's got two 00:34:25.40900:34:25.419 honking great electrolytic capacitors 00:34:27.18000:34:27.190 here across the battery input voltage to 00:34:29.49000:34:29.500 try and get rid of the noise that these 00:34:30.84000:34:30.850 things create mess of great electrolytic 00:34:33.24000:34:33.250 s-- but old school these days you'd 00:34:35.22000:34:35.230 probably use some really good ceramics 00:34:37.68000:34:37.690 to do that but do you sometimes you 00:34:39.36000:34:39.370 still get electrolytic so it'll do the 00:34:41.49000:34:41.500 job I know for example here's a Dell RC 00:34:45.50000:34:45.510 forum one and let me just pull out a bit 00:34:48.00000:34:48.010 so I can show you this is a forum one 00:34:49.38000:34:49.390 ESC and they come they actually provide 00:34:51.60000:34:51.610 an electrolytic in the package here here 00:34:54.48000:34:54.490 we go if I can give it out you go come 00:34:57.75000:34:57.760 on here's a low ESR electronic and we 00:35:00.51000:35:00.520 pullin of it because it's all a bit far 00:35:01.77000:35:01.780 away I pull it too far hang on it's a 00:35:05.43000:35:05.440 low ESR electrolytic that you can pop 00:35:07.41000:35:07.420 across the ESC to get rid of any noise 00:35:09.78000:35:09.790 that's created by it and it's part of 00:35:11.82000:35:11.830 the lot of what you get in the box 00:35:13.56000:35:13.570 basically with that forum on speed 00:35:15.75000:35:15.760 controller and here's a video 00:35:17.61000:35:17.620 transmitter 00:35:18.42000:35:18.430 it's a foxy at 200 milli watt video 00:35:19.86000:35:19.870 transmitter and you'll notice there's a 00:35:21.36000:35:21.370 lot of capacitors here all in parallel 00:35:23.58000:35:23.590 ceramic capacitors here again in 00:35:25.17000:35:25.180 parallel and I notice on this one there 00:35:26.91000:35:26.920 is a place here for a component that 00:35:28.86000:35:28.870 hasn't been used that's probably where 00:35:30.12000:35:30.130 they would put a tantalum capacitor but 00:35:33.03000:35:33.040 they probably found they didn't need it 00:35:34.14000:35:34.150 with all these ceramics so they just 00:35:36.30000:35:36.310 lift it off saves the scent here and the 00:35:37.83000:35:37.840 when you're making thousands of these it 00:35:38.94000:35:38.950 adds up to a bit of dollars in the long 00:35:40.38000:35:40.390 run so yeah these are just for power 00:35:42.36000:35:42.370 smoothie until here's the power supply 00:35:43.86000:35:43.870 this is what drops the voltage down from 00:35:45.93000:35:45.940 the input voltage which in this case can 00:35:47.73000:35:47.740 be I don't know what it is it's DC up to 00:35:49.95000:35:49.960 24 volts that'll drop it down to the 5 00:35:52.05000:35:52.060 volts or so that the circuit uses and 00:35:53.82000:35:53.830 having done that it drops it down by 00:35:55.83000:35:55.840 chopping it up and once you've chopped 00:35:57.78000:35:57.790 it up into little pulses you've got to 00:35:59.43000:35:59.440 fill in all the gaps so they put these 00:36:00.66000:36:00.670 capacitors here to smooth out the very 00:36:02.76000:36:02.770 very noisy output of this switched mode 00:36:04.83000:36:04.840 regulator so they're just acting again 00:36:06.69000:36:06.700 as reservoir caps and I've used ceramics 00:36:08.46000:36:08.470 because ceramics are very good this is a 00:36:10.92000:36:10.930 very high frequency switch mode power 00:36:12.27000:36:12.280 supply may even be as high as a few 00:36:14.40000:36:14.410 hundred kilohertz and the ceramics work 00:36:16.29000:36:16.300 really well at high frequencies so they 00:36:18.33000:36:18.340 probably didn't need this tantalum but 00:36:19.98000:36:19.990 if they've just used the tantalum 00:36:21.03000:36:21.040 probably wouldn't work so well because 00:36:22.83000:36:22.840 the high frequencies would have still 00:36:24.21000:36:24.220 been passing through them because these 00:36:25.89000:36:25.900 tent limbs not very good with very high 00:36:27.63000:36:27.640 frequencies ceramics ah so there you go 00:36:29.76000:36:29.770 there's another more capacitors and an 00:36:31.83000:36:31.840 everyday device and finally here's a 00:36:33.87000:36:33.880 foreign one your 4 button charges sorry 00:36:36.72000:36:36.730 here's a four button charger button 00:36:38.55000:36:38.560 button button I've taken it out of the 00:36:39.72000:36:39.730 box so you can see cuz I'm repairing it 00:36:41.28000:36:41.290 and you'll notice look at the size of 00:36:42.87000:36:42.880 that electrolytic capacitor it's a huge 00:36:44.67000:36:44.680 electrolytic capacitor there and there's 00:36:46.80000:36:46.810 those little score marks on the top huge 00:36:49.41000:36:49.420 electrolytic capacitor because this is 00:36:51.39000:36:51.400 handling quite large currents you know 00:36:53.91000:36:53.920 you'll charge up to 6 or 7 amps or 00:36:55.71000:36:55.720 something so you need to put a lot of 00:36:57.69000:36:57.700 capacitance across that in order to get 00:36:59.46000:36:59.470 the noise taken out we've got a little 00:37:01.88000:37:01.890 somewhere in here there'll be a switch 00:37:03.60000:37:03.610 mode regulator that we snipping the 00:37:05.82000:37:05.830 voltage up to be a boost back regulator 00:37:07.47000:37:07.480 and they'll have a really noisy upper so 00:37:09.15000:37:09.160 what you do is you put a big capacitor 00:37:10.59000:37:10.600 on it to smooth out all the noise to 00:37:12.09000:37:12.100 fill in all the gaps on the noise 00:37:13.11000:37:13.120 another capacitor over here first 00:37:15.09000:37:15.100 something for a probably the regulator 00:37:16.41000:37:16.420 for the digital circuitry so yeah that's 00:37:19.17000:37:19.180 what you get on there not much else in 00:37:22.38000:37:22.390 the world capacitors is a few ceramics 00:37:24.57000:37:24.580 probably hidden in there somewhere but 00:37:25.68000:37:25.690 yeah there's a use for your electrolytic 00:37:28.26000:37:28.270 so it's it for another dick Tuesday I 00:37:30.24000:37:30.250 hope I have been boozled you too much 00:37:32.37000:37:32.380 and I apologize to people who say it's 00:37:34.50000:37:34.510 not quite right because I always take a 00:37:35.79000:37:35.800 liberties to make things easier try and 00:37:37.50000:37:37.510 explain the concepts to you in a simple 00:37:38.97000:37:38.980 way so it's capacitors essential 00:37:41.25000:37:41.260 building block we may do some 00:37:42.42000:37:42.430 experiments on the bench when I've done 00:37:44.16000:37:44.170 I'll also do have done if I've done 00:37:45.87000:37:45.880 resistors I think I did Ohm's law but I 00:37:48.27000:37:48.280 may go looking a bit more at resistors 00:37:49.74000:37:49.750 have I haven't done it and we're looking 00:37:51.15000:37:51.160 in duck 00:37:51.52000:37:51.530 is because when you start putting these 00:37:52.87000:37:52.880 things together you can do some really 00:37:53.95000:37:53.960 cool stuff and of course semiconductors 00:37:56.05000:37:56.060 transistors fits that sort of thing 00:37:57.73000:37:57.740 that's a really important issue as well 00:37:58.93000:37:58.940 and you don't have to know how to use 00:38:00.31000:38:00.320 them but it really helps to know how 00:38:01.93000:38:01.940 they work and what makes them work so 00:38:04.20000:38:04.210 that you can understand better if 00:38:07.78000:38:07.790 something goes wrong or if why they're 00:38:09.76000:38:09.770 even there at all so that's it thank you 00:38:12.70000:38:12.710 for watching questions comes in the 00:38:13.90000:38:13.910 usual place I'm sorry this was a bit 00:38:15.70000:38:15.710 lighter than usual because I did this 00:38:17.95000:38:17.960 video two days ago and I forgot to turn 00:38:20.68000:38:20.690 on my microphone is it working now hello 00:38:23.29000:38:23.300 hello 00:38:23.77000:38:23.780 it is good yes so frustrating when that 00:38:26.95000:38:26.960 happens trust me anyway so I've had to 00:38:28.69000:38:28.700 do it again so this is actually tick 00:38:30.10000:38:30.110 Tuesday so for the 6th of November 2018 00:38:33.40000:38:33.410 on the 8th we're could enter yourself 00:38:35.77000:38:35.780 take Thursday you guys is it thank you 00:38:37.90000:38:37.910 for watching 00:38:38.32000:38:38.330 gotta go things to do bye for now 00:38:46.54900:38:46.559 okay now I'm gonna show you about the 00:38:49.14000:38:49.150 way that we can extract the AC if this 00:38:51.77900:38:51.789 was a signal on top of a DC because 00:38:53.25000:38:53.260 remember zero volts is way down there 00:38:54.92000:38:54.930 how do we just get that AC how do we 00:38:57.05900:38:57.069 block the DC well I'm going to use a 00:38:58.34900:38:58.359 capacitor here in series with my 00:39:00.39000:39:00.400 oscilloscope probe and that will 00:39:01.76900:39:01.779 effectively stop the DC but it'll lit 00:39:04.52900:39:04.539 the AC come through so let's just 00:39:06.02900:39:06.039 disconnect that for a moment put that 00:39:07.68000:39:07.690 onto there and I touch this onto here 00:39:09.42000:39:09.430 and there it is there's that signal 00:39:12.18000:39:12.190 still but there's no voltage on it it's 00:39:14.60900:39:14.619 just the AC part of that because I've 00:39:16.38000:39:16.390 got a capacitor in series with that 00:39:19.38000:39:19.390 thing has blocked the DC current the DC 00:39:21.50900:39:21.519 counts disappeared but the signal is 00:39:23.06900:39:23.079 still there just as I mentioned on the 00:39:25.20000:39:25.210 whiteboard must be true you saw it on 00:39:27.93000:39:27.940 the oscilloscope yeah 00:39:30.29900:39:30.309 I just got it resting on okay cookies
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