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>> So, here's a circuit for the flash.

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So, in order for you to understand how this works,

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you need a little bit of electronics background.

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But I'm going to do my best to try and explain

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at least intuitively how this circuit works.

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So, here's the single transistor I was telling you about.

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Here, the three resistors,

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one is here, one is here,

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and the other one is right there.

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I told you that there is a big electrolytic capacitor. That's this one.

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I said there is a neon electrolytic aluminum foil one.

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That's this one right here.

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I said there are two transformers,

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here's the first transformer,

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here is the second transformer,

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here's the neon flash shoot.

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That's the thing that flashes.

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I'm sorry, not the neon just a regular flash.

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Here is a little neon bulb.

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In the one that I just showed you,

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this was an LED,

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but it doesn't really matter, the concept is the same.

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So, sometimes they use the neon one here.

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Here's the trigger switch,

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then when you close the flash fires,

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here's the on and off switch. Let's go through this circuit.

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So, at the beginning the on and off switch is open.

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So, let's forget about everything that's on this side of the circuit.

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If this switch is open,

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and there is, therefore,

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no current going through the base,

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there is no voltage on the base.

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So, this bipolar transistor is turned off,

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so there is no current going down.

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As soon as you close the circuit,

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you can follow this connection.

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It goes through somewhere in the middle of the transformer and is

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connected to all the way up to 1.5 volts.

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So, you will bring some current and

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some voltage close to 1.5 volt at the base of this transistor

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which will quickly turn this transistor on

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causing a large current to go down from the collector to the emitter.

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Now, as soon as you induce a current,

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to go through this half of the transformer,

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this itself will cause a current to be induced on the other half of the transformer.

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But as soon as you do that,

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the current in here will then lower the voltage of

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the base to go down to even below zero.

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So, then the transistor turns off again.

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But when a transistor turns off this voltage will then eventually go

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back all the way up to 1.5 volts because the

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current will stop, and then the transistor will turn on again.

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So, this transistor turns itself on and

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off through this feedback path in the transformer.

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So, you could say that this portion of

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the circuit is essentially nothing more than an oscillator.

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So, by turning the transistor on and off quickly,

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you can induce a current in the transformer.

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Now, this center tab brings back a small voltage.

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It means that the entire voltage across

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the transformer does not appear at the base of this transistor.

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If it did, the transistor would die.

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So, they've taken only a part of that voltage down to the base of the transformer.

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But the whole transformer has a huge turn ratio.

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By that I mean, if you look at this circuit again,

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you can only see the outer coil,

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the outer coil of this transformer and I can count it has about six or seven turns only.

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That coil on the outside that you can see, that's this one.

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On the inside below that yellow tape is a whole bunch of other turns of this transformer,

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maybe about a thousand or a hundred times more than what is on the outside.

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So, that will cause a huge voltage difference

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between the primary coil and the secondary coil of the transformer, and

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that's how you are able to generate such a higher voltage using only a 1.5 volt supply.

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So, they take the high voltage portion

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of the output of the transformer and they connect it to this diode.

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They do that for a very specific reason.

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It's because the signal that appears here is AC.

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It's AC, why? Because it's an oscillator.

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Because it turns on and off constantly.

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That AC voltage will go below zero by several 100 volts every time on this down cycle.

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This diode will only conduct current when

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the voltage on this side is lower than the voltage on this side.

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So, every time this voltage goes well below zero,

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this big capacitor, which is the main capacitor of

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the flash gets charged a little bit more.

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So, every time during every oscillation cycle you will

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put a little bit more charge into this big capacitor.

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So, the voltage at the output of the capacitor is a DC voltage

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but the voltage on the other side of the diode is an AC voltage.

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So, you essentially have built what's called a peak detector,

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where you'll keep dumping

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more and more and more voltage charge

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into this capacitor and the capacitor begins to charge up.

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We will take a look at it under a oscilloscope so we can

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see the oscillation very clearly.

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So, this guy will then eventually charge up to minus 350 volts.

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The reason I say minus 350 volts is because

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I'm measuring everything with the respect to the ground of the battery.

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So, if you assume that this is a zero volts,

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every time this thing spikes well below zero,

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the diode conducts and

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the positive terminal of the capacitor is actually connected to ground.

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So, this knot can go all the way down to minus 350 volts.

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The other side of this now,

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there's a whole bunch of other circuits that is

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responsible for actually triggering the flash.

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So, there's a big resistor that

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separates this half of the circuit from this half the circuit.

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So, this is a big capacitor here that's charged up,

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and that capacitor is connected on one side of the flash tube,

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the other side of the flash tube is grounded.

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On this side here we have the neon light or the LED,

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and a big resistor in series.

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So, if this voltage gets high enough, meaning when the flash is ready to be fired,

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the light turns on, it's just an indicator to let you as the user

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know that the flash will fire once you push the shutter button.

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So, this portion of the circuit is only an indicator.

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Then you have another capacitor here much smaller than this one that will

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charge to about the same voltage as this capacitor.

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So, as time passes and the flash is charged up,

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slowly current will flow through here and charge

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up this capacitor to the same voltage as this one.

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This is a much smaller capacitor,

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and here's the triggers switch on the other side and another transformer.

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So, the way that flash tube works is that even though we are

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putting zero volts here and minus 350 volts here,

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that's not enough to initiate the flash,

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because the potential is not big enough for a spark to form inside the flash tube.

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So, you need to kick it.

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You need to initiate

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it for the current to start flowing and once the current starts to flow,

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then the path, the short-circuit happens in the middle of

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the flash, and then you get the flash which is a spark.

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So, in order to kick it and initiate the current,

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you need to put a very,

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very large voltage, in this case,

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a very large negative voltage right here to dry the electrons into the tube.

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Once you dry the electrons in the tube, then you will fire the flash.

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This is done through this transformer and this capacitor.

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So, if I close this circuit quickly,

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which is done by connecting these two wires together very briefly,

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it will discharge this capacitor through

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this inductor half of the transformer and to ground.

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So, there will be a burst of current,

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a lot of it but for a very short time right through

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this transformer which will then cause even a bigger,

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because this transformer has a big turn ratio,

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a bigger voltage on the other side.

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So, for a very brief time,

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something close to minus 2,000 volts appears

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here for a very short time and that initiates the flash,

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causes the electrons to be drawn into

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the tube and all the way to the other side and to ground,

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and then you get the big bright light that you see.

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So, this entire circuit is everything that's on this.

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I haven't omitted anything that is on this circuit that you just saw.

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So, by looking at this,

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we should be able to make some predictions well,

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we should be able to put our oscilloscope at this node,

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and look at the waveform that I told you.

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We should be able to measure a very large negative voltage at this node.

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Of course, we should be able to see this light turn on.

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We will do all of those things right now,

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and we'll also take a look at how you would measure something like that.

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Then, at the very end,

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we'll see how we can use this in

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combination with a Nixie tube and do some experiments there.

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So, in order to make the experiments safer,

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I've taken one of these flash and I've removed

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the components that I don't need to and I have some wires to it.

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So, it can be easily connected to a power supply,

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and we can measure currents and voltages and so on.

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So, for example these battery holders, I don't need,

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I'm not going to be using the flash itself

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anymore because I want to use it for Nixie tube,

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so I can remove that and sought of some wires to it so then,

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I ended up with something that looks like this.

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So, exactly the same circuit, everything is the same.

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I've removed the flash, the capacitors there,

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and you can see this one actually uses a,

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this thing will focus.

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This thing uses a little neon tube as

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opposed to an LED to tell you when the flash is charged.

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So, a little bit different but it's the same circuit.

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I have also connected a piece of metal size,

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a piece the metal across the on and off terminal,

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to permanently keep it in the on position.

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So, this would make it a little bit easier for me to do some experiments with it.

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I've also removed the low trigger and put a jumper there in its place.

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Wire that I inserted through, this wires is just

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that across the plus and minus terminal of the flash.

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I can connect this to my power supply,

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and then we can check to see what is the voltage on the capacitor?

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How long does it take to charge that?

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Then we will do one discharge cycle by short circuiting

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the capacitors which is not recommended, just for entertainment.

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Also, then we will show you the wave from the oscilloscope,

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and then we'll get to the Nixie tube.

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So, let's see what I can do.

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So, I'm going to take the positive and the negative terminals.

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I'm going to connect them to my power supply.

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So, here's a positive,

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here is a negative terminal, so I'll put that down.

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I will take the positive and the negative terminal of the multi-meter.

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I'm going to connect it across the capacitor.

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So, I'm going to connect a negative toward the ground of this power supply would be.

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That's the positive terminal of the capacitor,

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and I will take the other wire and connected to negative terminal of the capacitor.

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So, what I'm doing here is that I'm using my power supply to power the flash.

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I am measuring the voltage across the capacitor directly.

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You will be able to move this side away,

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you will be able to see at the same time the voltage that I'm applying to the flash unit.

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You will be able to see a current that the flash unit takes.

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It will show up right here,

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and you will be able to see the voltage across the capacitor.

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So, right now the voltage across the capacitor is minus 5.2 volts approximately,

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it's the residue from the last time that I charged it.

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So, let's do that.

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I'm going to turn the power supply on.

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So, right now it says zero volts at zero amps. Is that makes sense?

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I'm going to slowly raise this voltage at all the way up to 1.5 volts,

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and since I have already started the on and off button shut,

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it will start charging right away.

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So, at the very beginning,

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up to about 0.5 volts,

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you will get nothing because its bipolar transistor hasn't turned on yet.

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So, as soon as you go about 0.6 volts, right there, now,

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the flash is starting to charge up the capacitor and you can see the voltage here

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is already on minus a 115 volts and it keeps rising slowly.

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Minus a 123 votes,

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but this is only a 0.6 volt.

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An alkaline battery, a double A battery can go all the way up to 1.5.

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So let's do that, 1.5 volts.

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We'll wait a little bit until this thing charges.

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You can see draws a lot of current at the beginning of is drawing almost an Amp.

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So, right now the current keeps going down.

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So, that makes sense of course because the current

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keeps going down because the capacitor keeps charging.

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So, resists loading on it.

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At the same time, you can see the voltage appear now is at 324 minus 326-7 volts.

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If I turn this, I have to be very very careful handling this nap very very careful.

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So, if I shift it over,

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you can see that little light flashing.

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That's the little neon light I was telling you about.

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Let me bring it up a bit closer to the camera.

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Hopefully, we'll focus on it.

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Well, you can see the neon flash going on and off.

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There is actually a little quiz in this episode that I like to see

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you guys try and discuss it on

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the forum or on the comments sections of the YouTube channel.

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The question I have for you is,

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can you tell me why does this light flash?

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I can tell you that in the LED version,

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if I were to replace this with an LED,

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the LED would not flash.

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So, let me know why you think this is flashing.

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So, let's put this down.

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So, now I have charged the capacitor to minus 350 volts.

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There's still some about 296 milliamps of current going through it.

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If you leave this for a while longer,

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it's not going to go much more than that.

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It's going to go about minus 358 volts.

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Its probably going to have it around that point.

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So, now that capacitor is fully charged, so

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what I'm going to do is,

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I'm going to turn the power supply off.

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So, there's no more current going in it.

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You can see this voltage will start to slowly fall for

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many reasons that the flashing light is of course is consuming some power,

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there's leakage through the capacitor and so on.

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So, that voltage will continue to go down.

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So, let me get something to discharge it.