WEBVTT 00:00:00.230 --> 00:00:03.405 >> So, here's a circuit for the flash. 00:00:03.405 --> 00:00:05.820 So, in order for you to understand how this works, 00:00:05.820 --> 00:00:08.520 you need a little bit of electronics background. 00:00:08.520 --> 00:00:10.965 But I'm going to do my best to try and explain 00:00:10.965 --> 00:00:14.250 at least intuitively how this circuit works. 00:00:14.250 --> 00:00:16.770 So, here's the single transistor I was telling you about. 00:00:16.770 --> 00:00:19.035 Here, the three resistors, 00:00:19.035 --> 00:00:21.150 one is here, one is here, 00:00:21.150 --> 00:00:22.890 and the other one is right there. 00:00:22.890 --> 00:00:26.445 I told you that there is a big electrolytic capacitor. That's this one. 00:00:26.445 --> 00:00:29.690 I said there is a neon electrolytic aluminum foil one. 00:00:29.690 --> 00:00:30.965 That's this one right here. 00:00:30.965 --> 00:00:33.125 I said there are two transformers, 00:00:33.125 --> 00:00:34.550 here's the first transformer, 00:00:34.550 --> 00:00:36.100 here is the second transformer, 00:00:36.100 --> 00:00:37.920 here's the neon flash shoot. 00:00:37.920 --> 00:00:39.600 That's the thing that flashes. 00:00:39.600 --> 00:00:42.465 I'm sorry, not the neon just a regular flash. 00:00:42.465 --> 00:00:44.265 Here is a little neon bulb. 00:00:44.265 --> 00:00:46.170 In the one that I just showed you, 00:00:46.170 --> 00:00:47.325 this was an LED, 00:00:47.325 --> 00:00:49.755 but it doesn't really matter, the concept is the same. 00:00:49.755 --> 00:00:51.900 So, sometimes they use the neon one here. 00:00:51.900 --> 00:00:53.790 Here's the trigger switch, 00:00:53.790 --> 00:00:55.590 then when you close the flash fires, 00:00:55.590 --> 00:00:59.535 here's the on and off switch. Let's go through this circuit. 00:00:59.535 --> 00:01:03.000 So, at the beginning the on and off switch is open. 00:01:03.000 --> 00:01:05.735 So, let's forget about everything that's on this side of the circuit. 00:01:05.735 --> 00:01:07.340 If this switch is open, 00:01:07.340 --> 00:01:09.950 and there is, therefore, 00:01:09.950 --> 00:01:11.120 no current going through the base, 00:01:11.120 --> 00:01:12.425 there is no voltage on the base. 00:01:12.425 --> 00:01:15.370 So, this bipolar transistor is turned off, 00:01:15.370 --> 00:01:17.030 so there is no current going down. 00:01:17.030 --> 00:01:19.445 As soon as you close the circuit, 00:01:19.445 --> 00:01:21.620 you can follow this connection. 00:01:21.620 --> 00:01:24.140 It goes through somewhere in the middle of the transformer and is 00:01:24.140 --> 00:01:26.630 connected to all the way up to 1.5 volts. 00:01:26.630 --> 00:01:29.420 So, you will bring some current and 00:01:29.420 --> 00:01:32.735 some voltage close to 1.5 volt at the base of this transistor 00:01:32.735 --> 00:01:35.630 which will quickly turn this transistor on 00:01:35.630 --> 00:01:39.110 causing a large current to go down from the collector to the emitter. 00:01:39.110 --> 00:01:41.950 Now, as soon as you induce a current, 00:01:41.950 --> 00:01:45.900 to go through this half of the transformer, 00:01:45.900 --> 00:01:52.005 this itself will cause a current to be induced on the other half of the transformer. 00:01:52.005 --> 00:01:53.605 But as soon as you do that, 00:01:53.605 --> 00:01:56.090 the current in here will then lower the voltage of 00:01:56.090 --> 00:01:58.820 the base to go down to even below zero. 00:01:58.820 --> 00:02:01.430 So, then the transistor turns off again. 00:02:01.430 --> 00:02:06.140 But when a transistor turns off this voltage will then eventually go 00:02:06.140 --> 00:02:08.389 back all the way up to 1.5 volts because the 00:02:08.389 --> 00:02:11.060 current will stop, and then the transistor will turn on again. 00:02:11.060 --> 00:02:14.120 So, this transistor turns itself on and 00:02:14.120 --> 00:02:18.335 off through this feedback path in the transformer. 00:02:18.335 --> 00:02:20.810 So, you could say that this portion of 00:02:20.810 --> 00:02:24.020 the circuit is essentially nothing more than an oscillator. 00:02:24.020 --> 00:02:27.710 So, by turning the transistor on and off quickly, 00:02:27.710 --> 00:02:30.360 you can induce a current in the transformer. 00:02:30.360 --> 00:02:33.560 Now, this center tab brings back a small voltage. 00:02:33.560 --> 00:02:35.900 It means that the entire voltage across 00:02:35.900 --> 00:02:39.440 the transformer does not appear at the base of this transistor. 00:02:39.440 --> 00:02:41.990 If it did, the transistor would die. 00:02:41.990 --> 00:02:46.610 So, they've taken only a part of that voltage down to the base of the transformer. 00:02:46.610 --> 00:02:49.985 But the whole transformer has a huge turn ratio. 00:02:49.985 --> 00:02:53.450 By that I mean, if you look at this circuit again, 00:02:53.450 --> 00:02:56.640 you can only see the outer coil, 00:02:56.640 --> 00:03:01.785 the outer coil of this transformer and I can count it has about six or seven turns only. 00:03:01.785 --> 00:03:05.600 That coil on the outside that you can see, that's this one. 00:03:05.600 --> 00:03:12.690 On the inside below that yellow tape is a whole bunch of other turns of this transformer, 00:03:12.690 --> 00:03:17.330 maybe about a thousand or a hundred times more than what is on the outside. 00:03:17.330 --> 00:03:20.150 So, that will cause a huge voltage difference 00:03:20.150 --> 00:03:23.450 between the primary coil and the secondary coil of the transformer, and 00:03:23.450 --> 00:03:30.035 that's how you are able to generate such a higher voltage using only a 1.5 volt supply. 00:03:30.035 --> 00:03:33.230 So, they take the high voltage portion 00:03:33.230 --> 00:03:36.335 of the output of the transformer and they connect it to this diode. 00:03:36.335 --> 00:03:39.840 They do that for a very specific reason. 00:03:39.840 --> 00:03:42.935 It's because the signal that appears here is AC. 00:03:42.935 --> 00:03:45.095 It's AC, why? Because it's an oscillator. 00:03:45.095 --> 00:03:47.150 Because it turns on and off constantly. 00:03:47.150 --> 00:03:54.240 That AC voltage will go below zero by several 100 volts every time on this down cycle. 00:03:54.240 --> 00:03:57.650 This diode will only conduct current when 00:03:57.650 --> 00:04:00.860 the voltage on this side is lower than the voltage on this side. 00:04:00.860 --> 00:04:04.450 So, every time this voltage goes well below zero, 00:04:04.450 --> 00:04:07.580 this big capacitor, which is the main capacitor of 00:04:07.580 --> 00:04:11.240 the flash gets charged a little bit more. 00:04:11.240 --> 00:04:15.500 So, every time during every oscillation cycle you will 00:04:15.500 --> 00:04:20.269 put a little bit more charge into this big capacitor. 00:04:20.269 --> 00:04:23.450 So, the voltage at the output of the capacitor is a DC voltage 00:04:23.450 --> 00:04:26.840 but the voltage on the other side of the diode is an AC voltage. 00:04:26.840 --> 00:04:30.470 So, you essentially have built what's called a peak detector, 00:04:30.470 --> 00:04:31.610 where you'll keep dumping 00:04:31.610 --> 00:04:34.010 more and more and more voltage charge 00:04:34.010 --> 00:04:37.745 into this capacitor and the capacitor begins to charge up. 00:04:37.745 --> 00:04:40.340 We will take a look at it under a oscilloscope so we can 00:04:40.340 --> 00:04:42.410 see the oscillation very clearly. 00:04:42.410 --> 00:04:48.760 So, this guy will then eventually charge up to minus 350 volts. 00:04:48.760 --> 00:04:51.260 The reason I say minus 350 volts is because 00:04:51.260 --> 00:04:53.950 I'm measuring everything with the respect to the ground of the battery. 00:04:53.950 --> 00:04:56.775 So, if you assume that this is a zero volts, 00:04:56.775 --> 00:04:59.500 every time this thing spikes well below zero, 00:04:59.500 --> 00:05:00.980 the diode conducts and 00:05:00.980 --> 00:05:03.950 the positive terminal of the capacitor is actually connected to ground. 00:05:03.950 --> 00:05:08.005 So, this knot can go all the way down to minus 350 volts. 00:05:08.005 --> 00:05:09.885 The other side of this now, 00:05:09.885 --> 00:05:11.690 there's a whole bunch of other circuits that is 00:05:11.690 --> 00:05:14.570 responsible for actually triggering the flash. 00:05:14.570 --> 00:05:16.630 So, there's a big resistor that 00:05:16.630 --> 00:05:20.030 separates this half of the circuit from this half the circuit. 00:05:20.030 --> 00:05:22.810 So, this is a big capacitor here that's charged up, 00:05:22.810 --> 00:05:26.780 and that capacitor is connected on one side of the flash tube, 00:05:26.780 --> 00:05:29.035 the other side of the flash tube is grounded. 00:05:29.035 --> 00:05:33.290 On this side here we have the neon light or the LED, 00:05:33.290 --> 00:05:34.760 and a big resistor in series. 00:05:34.760 --> 00:05:40.265 So, if this voltage gets high enough, meaning when the flash is ready to be fired, 00:05:40.265 --> 00:05:43.820 the light turns on, it's just an indicator to let you as the user 00:05:43.820 --> 00:05:47.545 know that the flash will fire once you push the shutter button. 00:05:47.545 --> 00:05:51.135 So, this portion of the circuit is only an indicator. 00:05:51.135 --> 00:05:55.190 Then you have another capacitor here much smaller than this one that will 00:05:55.190 --> 00:05:59.430 charge to about the same voltage as this capacitor. 00:05:59.430 --> 00:06:02.120 So, as time passes and the flash is charged up, 00:06:02.120 --> 00:06:04.280 slowly current will flow through here and charge 00:06:04.280 --> 00:06:06.605 up this capacitor to the same voltage as this one. 00:06:06.605 --> 00:06:08.150 This is a much smaller capacitor, 00:06:08.150 --> 00:06:12.010 and here's the triggers switch on the other side and another transformer. 00:06:12.010 --> 00:06:15.440 So, the way that flash tube works is that even though we are 00:06:15.440 --> 00:06:18.890 putting zero volts here and minus 350 volts here, 00:06:18.890 --> 00:06:21.880 that's not enough to initiate the flash, 00:06:21.880 --> 00:06:26.750 because the potential is not big enough for a spark to form inside the flash tube. 00:06:26.750 --> 00:06:28.205 So, you need to kick it. 00:06:28.205 --> 00:06:29.840 You need to initiate 00:06:29.840 --> 00:06:35.080 it for the current to start flowing and once the current starts to flow, 00:06:35.080 --> 00:06:37.490 then the path, the short-circuit happens in the middle of 00:06:37.490 --> 00:06:39.890 the flash, and then you get the flash which is a spark. 00:06:39.890 --> 00:06:42.800 So, in order to kick it and initiate the current, 00:06:42.800 --> 00:06:44.300 you need to put a very, 00:06:44.300 --> 00:06:46.010 very large voltage, in this case, 00:06:46.010 --> 00:06:50.870 a very large negative voltage right here to dry the electrons into the tube. 00:06:50.870 --> 00:06:54.530 Once you dry the electrons in the tube, then you will fire the flash. 00:06:54.530 --> 00:06:58.250 This is done through this transformer and this capacitor. 00:06:58.250 --> 00:07:00.605 So, if I close this circuit quickly, 00:07:00.605 --> 00:07:06.530 which is done by connecting these two wires together very briefly, 00:07:06.530 --> 00:07:10.340 it will discharge this capacitor through 00:07:10.340 --> 00:07:14.150 this inductor half of the transformer and to ground. 00:07:14.150 --> 00:07:16.700 So, there will be a burst of current, 00:07:16.700 --> 00:07:20.090 a lot of it but for a very short time right through 00:07:20.090 --> 00:07:23.595 this transformer which will then cause even a bigger, 00:07:23.595 --> 00:07:25.950 because this transformer has a big turn ratio, 00:07:25.950 --> 00:07:27.770 a bigger voltage on the other side. 00:07:27.770 --> 00:07:30.590 So, for a very brief time, 00:07:30.590 --> 00:07:33.920 something close to minus 2,000 volts appears 00:07:33.920 --> 00:07:37.670 here for a very short time and that initiates the flash, 00:07:37.670 --> 00:07:39.530 causes the electrons to be drawn into 00:07:39.530 --> 00:07:42.155 the tube and all the way to the other side and to ground, 00:07:42.155 --> 00:07:44.600 and then you get the big bright light that you see. 00:07:44.600 --> 00:07:47.900 So, this entire circuit is everything that's on this. 00:07:47.900 --> 00:07:52.610 I haven't omitted anything that is on this circuit that you just saw. 00:07:52.610 --> 00:07:54.680 So, by looking at this, 00:07:54.680 --> 00:07:57.500 we should be able to make some predictions well, 00:07:57.500 --> 00:08:00.805 we should be able to put our oscilloscope at this node, 00:08:00.805 --> 00:08:03.670 and look at the waveform that I told you. 00:08:03.670 --> 00:08:07.520 We should be able to measure a very large negative voltage at this node. 00:08:07.520 --> 00:08:10.630 Of course, we should be able to see this light turn on. 00:08:10.630 --> 00:08:12.450 We will do all of those things right now, 00:08:12.450 --> 00:08:15.950 and we'll also take a look at how you would measure something like that. 00:08:15.950 --> 00:08:17.450 Then, at the very end, 00:08:17.450 --> 00:08:19.550 we'll see how we can use this in 00:08:19.550 --> 00:08:23.190 combination with a Nixie tube and do some experiments there. 00:08:23.510 --> 00:08:26.520 So, in order to make the experiments safer, 00:08:26.520 --> 00:08:29.325 I've taken one of these flash and I've removed 00:08:29.325 --> 00:08:32.655 the components that I don't need to and I have some wires to it. 00:08:32.655 --> 00:08:34.830 So, it can be easily connected to a power supply, 00:08:34.830 --> 00:08:37.485 and we can measure currents and voltages and so on. 00:08:37.485 --> 00:08:40.210 So, for example these battery holders, I don't need, 00:08:40.210 --> 00:08:42.700 I'm not going to be using the flash itself 00:08:42.700 --> 00:08:45.730 anymore because I want to use it for Nixie tube, 00:08:45.730 --> 00:08:48.760 so I can remove that and sought of some wires to it so then, 00:08:48.760 --> 00:08:52.300 I ended up with something that looks like this. 00:08:52.300 --> 00:08:55.435 So, exactly the same circuit, everything is the same. 00:08:55.435 --> 00:08:57.805 I've removed the flash, the capacitors there, 00:08:57.805 --> 00:09:00.925 and you can see this one actually uses a, 00:09:00.925 --> 00:09:03.125 this thing will focus. 00:09:03.125 --> 00:09:06.030 This thing uses a little neon tube as 00:09:06.030 --> 00:09:09.030 opposed to an LED to tell you when the flash is charged. 00:09:09.030 --> 00:09:11.520 So, a little bit different but it's the same circuit. 00:09:11.520 --> 00:09:14.715 I have also connected a piece of metal size, 00:09:14.715 --> 00:09:17.600 a piece the metal across the on and off terminal, 00:09:17.600 --> 00:09:20.440 to permanently keep it in the on position. 00:09:20.440 --> 00:09:25.240 So, this would make it a little bit easier for me to do some experiments with it. 00:09:25.240 --> 00:09:30.590 I've also removed the low trigger and put a jumper there in its place. 00:09:30.660 --> 00:09:33.520 Wire that I inserted through, this wires is just 00:09:33.520 --> 00:09:36.130 that across the plus and minus terminal of the flash. 00:09:36.130 --> 00:09:38.605 I can connect this to my power supply, 00:09:38.605 --> 00:09:43.480 and then we can check to see what is the voltage on the capacitor? 00:09:43.480 --> 00:09:44.960 How long does it take to charge that? 00:09:44.960 --> 00:09:47.740 Then we will do one discharge cycle by short circuiting 00:09:47.740 --> 00:09:50.890 the capacitors which is not recommended, just for entertainment. 00:09:50.890 --> 00:09:54.430 Also, then we will show you the wave from the oscilloscope, 00:09:54.430 --> 00:09:56.770 and then we'll get to the Nixie tube. 00:09:56.770 --> 00:09:58.750 So, let's see what I can do. 00:09:58.750 --> 00:10:03.565 So, I'm going to take the positive and the negative terminals. 00:10:03.565 --> 00:10:07.795 I'm going to connect them to my power supply. 00:10:07.795 --> 00:10:09.670 So, here's a positive, 00:10:09.670 --> 00:10:12.640 here is a negative terminal, so I'll put that down. 00:10:12.640 --> 00:10:17.170 I will take the positive and the negative terminal of the multi-meter. 00:10:17.170 --> 00:10:19.510 I'm going to connect it across the capacitor. 00:10:19.510 --> 00:10:24.130 So, I'm going to connect a negative toward the ground of this power supply would be. 00:10:24.130 --> 00:10:27.280 That's the positive terminal of the capacitor, 00:10:27.280 --> 00:10:33.220 and I will take the other wire and connected to negative terminal of the capacitor. 00:10:33.220 --> 00:10:38.620 So, what I'm doing here is that I'm using my power supply to power the flash. 00:10:38.620 --> 00:10:41.740 I am measuring the voltage across the capacitor directly. 00:10:41.740 --> 00:10:45.175 You will be able to move this side away, 00:10:45.175 --> 00:10:53.665 you will be able to see at the same time the voltage that I'm applying to the flash unit. 00:10:53.665 --> 00:10:56.290 You will be able to see a current that the flash unit takes. 00:10:56.290 --> 00:10:57.445 It will show up right here, 00:10:57.445 --> 00:11:00.430 and you will be able to see the voltage across the capacitor. 00:11:00.430 --> 00:11:05.845 So, right now the voltage across the capacitor is minus 5.2 volts approximately, 00:11:05.845 --> 00:11:08.380 it's the residue from the last time that I charged it. 00:11:08.380 --> 00:11:10.030 So, let's do that. 00:11:10.030 --> 00:11:12.070 I'm going to turn the power supply on. 00:11:12.070 --> 00:11:15.925 So, right now it says zero volts at zero amps. Is that makes sense? 00:11:15.925 --> 00:11:20.020 I'm going to slowly raise this voltage at all the way up to 1.5 volts, 00:11:20.020 --> 00:11:24.205 and since I have already started the on and off button shut, 00:11:24.205 --> 00:11:25.825 it will start charging right away. 00:11:25.825 --> 00:11:27.280 So, at the very beginning, 00:11:27.280 --> 00:11:28.750 up to about 0.5 volts, 00:11:28.750 --> 00:11:32.800 you will get nothing because its bipolar transistor hasn't turned on yet. 00:11:32.800 --> 00:11:37.030 So, as soon as you go about 0.6 volts, right there, now, 00:11:37.030 --> 00:11:41.140 the flash is starting to charge up the capacitor and you can see the voltage here 00:11:41.140 --> 00:11:45.295 is already on minus a 115 volts and it keeps rising slowly. 00:11:45.295 --> 00:11:47.155 Minus a 123 votes, 00:11:47.155 --> 00:11:49.045 but this is only a 0.6 volt. 00:11:49.045 --> 00:11:52.810 An alkaline battery, a double A battery can go all the way up to 1.5. 00:11:52.810 --> 00:11:58.195 So let's do that, 1.5 volts. 00:11:58.195 --> 00:12:00.850 We'll wait a little bit until this thing charges. 00:12:00.850 --> 00:12:04.615 You can see draws a lot of current at the beginning of is drawing almost an Amp. 00:12:04.615 --> 00:12:07.765 So, right now the current keeps going down. 00:12:07.765 --> 00:12:09.640 So, that makes sense of course because the current 00:12:09.640 --> 00:12:11.800 keeps going down because the capacitor keeps charging. 00:12:11.800 --> 00:12:13.345 So, resists loading on it. 00:12:13.345 --> 00:12:20.530 At the same time, you can see the voltage appear now is at 324 minus 326-7 volts. 00:12:20.530 --> 00:12:24.835 If I turn this, I have to be very very careful handling this nap very very careful. 00:12:24.835 --> 00:12:26.710 So, if I shift it over, 00:12:26.710 --> 00:12:28.735 you can see that little light flashing. 00:12:28.735 --> 00:12:31.300 That's the little neon light I was telling you about. 00:12:31.300 --> 00:12:33.775 Let me bring it up a bit closer to the camera. 00:12:33.775 --> 00:12:36.710 Hopefully, we'll focus on it. 00:12:38.130 --> 00:12:42.940 Well, you can see the neon flash going on and off. 00:12:42.940 --> 00:12:49.585 There is actually a little quiz in this episode that I like to see 00:12:49.585 --> 00:12:52.390 you guys try and discuss it on 00:12:52.390 --> 00:12:56.590 the forum or on the comments sections of the YouTube channel. 00:12:56.590 --> 00:12:58.420 The question I have for you is, 00:12:58.420 --> 00:13:01.675 can you tell me why does this light flash? 00:13:01.675 --> 00:13:04.360 I can tell you that in the LED version, 00:13:04.360 --> 00:13:06.070 if I were to replace this with an LED, 00:13:06.070 --> 00:13:07.900 the LED would not flash. 00:13:07.900 --> 00:13:10.705 So, let me know why you think this is flashing. 00:13:10.705 --> 00:13:13.075 So, let's put this down. 00:13:13.075 --> 00:13:18.775 So, now I have charged the capacitor to minus 350 volts. 00:13:18.775 --> 00:13:24.640 There's still some about 296 milliamps of current going through it. 00:13:24.640 --> 00:13:26.665 If you leave this for a while longer, 00:13:26.665 --> 00:13:29.290 it's not going to go much more than that. 00:13:29.290 --> 00:13:31.360 It's going to go about minus 358 volts. 00:13:31.360 --> 00:13:33.265 Its probably going to have it around that point. 00:13:33.265 --> 00:13:36.160 So, now that capacitor is fully charged, so 00:13:36.160 --> 00:13:37.960 what I'm going to do is, 00:13:37.960 --> 00:13:40.975 I'm going to turn the power supply off. 00:13:40.975 --> 00:13:43.315 So, there's no more current going in it. 00:13:43.315 --> 00:13:46.720 You can see this voltage will start to slowly fall for 00:13:46.720 --> 00:13:50.665 many reasons that the flashing light is of course is consuming some power, 00:13:50.665 --> 00:13:52.840 there's leakage through the capacitor and so on. 00:13:52.840 --> 00:13:54.700 So, that voltage will continue to go down. 00:13:54.700 --> 00:13:57.500 So, let me get something to discharge it.