Name: 我們的LED電路｜數碼電子產品（3 of 10）。 (Powering our LED circuit | Digital electronics (3 of 10))
Uploaded: 2021-01-14T10:16:11.000Z
Duration: 13 min 22 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

In the last video, we built this circuit with Anneli D and a resistor.

情態副詞

And the reason we were using this resistor to limit the current through the l E D s so that so that the led would only draw.

Um, you know, the 20 million pes of current and it would and the resistor would drop any excess voltage so the led would would only would only operate at the at the 1.9 or two volts that it requires.

And we were connected up to this laboratory power supply that allowed us to adjust the voltage with with quite a bit of precision.

But now that we have this resistor in here, we don't need that that precise bolted source anymore.

And we can we can look at some other options, which which is great if you want to build this at home and you don't happen to have a very expensive power supply.

So let me make a little bit more room here and one of the other options or the most convenient option maybe is a battery.

So this is just a simple nine volt battery and again because we saw with a resistor particularly this.

This is a 1000 Omar one kilo ohm resistor.

Um, we can we can put quite a bit more voltage in here, and the resistor will drop the excess voltage.

And so the easy way to do this is with one of these little, um, one of these little battery snaps here and to the battery just snaps into here, and then you can you can connect this to the circuit and so will connect.

Um, just the same way the negative side here, on the positive side here, that corresponds to the way that the league is connected.

And then if we connect the battery, the led lights up so pretty simple and you and you can certainly try this at home.

Uh, and if we're interested, so it looks like the led is working fine.

It's ah, you know, reasonable, Reasonably bright.

Um, it doesn't appear to be, uh, you know, hot or drawing too much current.

Nothing's smells like it's burning, which is always, always a good sign.

But if you're interested to see just exactly how much voltage the led is drawing, we can measure the voltage across it.

If you have if you have a volt meter, um, any any volt meter will d'oh!

Um, I'll use I'll use this one, but you can use any any volt meter you have, and we'll just set it to DC voltage.

And it says that it's measuring volts DC and first, what I'll do is I'll measure the voltage across the entire circuit.

So from this side, where the where the negative terminals coming in from the battery to the positive terminal and you see it says it's about nine volts, Which makes sense because we have a nine volt battery.

Um, now the resistor is supposedly dropping some voltage, said the led operates with the appropriate voltage.

And if we look at what the manufacturer says, manufacturer members said that this led should have between 1.9 and two volts, and it seems to be operating fine.

So hopefully that's the voltage that it's getting.

If not, then we need to kind of maybe looking at maybe a different value for that resistor.

So if I look at the voltage across this led, I see 1.95 you know, we're so volts, which is right, right in that range from 1.922 volts, which is which is perfect and explains why the led is working just fine.

And just one more thing I'll measure is look at the voltage on the resistor.

So from this side of the resistor to the other side, I see 7.12 volts, which makes sense.

The led is dropping 1.95 volts and the battery is providing nine volts, which all makes sense.

So if you have the batteries plus nine, the resistor is dropping 7.1.

All of that together cancels out and we are obeying Kershaw fs voltage law, which is that the all of the voltage sources add to zero.

And so, in this case, the battery is a positive altered source and then the drops across each component is a negative voltage source, and all of that adds zero, which which works out nicely.

So this is a great way that you can build this circuit at home.

Another way that I actually really like is instead of using a battery.

One of things about batteries, of course, is that, you know, they get used up and you have to have to buy new ones or recharge them.

Um, so what I what I find is convenient, actually.

Make sure I disconnect this here so that we don't short this and can damage the battery.

What I find is convenient is these little USB chargers.

So this plugs into the wall, of course, and it gives you USB and U S B has a five volt, um, a five old D c voltage available on it.

And so you can use these things, which you probably might have around the house.

Or you can get relatively inexpensively and you could get five votes out of this and just to double check if we wait, take a close look at this and you should check.

If you're using one of these, you should check the one you're using.

But let me just take you, see if I can zoom in here.

If we look very closely right here, it'll say input is 100 to 240 volts.

50 60 hertz at 0.15 amps and that and that matches what you would get from from the power source from the wall in the U.

And this little symbol here means means D c direct current, which is what we want.

So five volts, it upto one amp is what we get out of this.

So in order to in order to use this, we need to find some way to kind of plug in to the other side of here and get the five bolts out.

And so a way to do that is to get an old USB cable or one that you don't you don't need or don't, um, aren't using for anything else.

And let me let me zoom out here just a little bit more.

So this is just a USB cable In this end, of course, plugs into the wall adapter, and this other end is this is just like a mini USB.

But what we want to do is plug into the bread board, so this isn't gonna plug in here.

So what I could d'oh is just and again, This is obviously one that I'm not using for.

Anything else is I could just cut this off.

And, of course, don't do this while it's plugged in.

And if I If I kind of dig into this, um, she's here.

Oh, may just kind of nibble away at the outside chief, and I'm being very careful not to cut the wires inside.

So I'm just taking this little plastic sheath off and money zoom in a little bit so you can kind of see what I'm doing.

But what I've done is I'm taking the outside plastic off and inside.

There's some shielding, it looks like, and you may find something different when you take apart your USB cable.

But inside there's some shielding, and inside of that there's some other little wires that we want to get at.

So let me try toe cut some of the shielding apart.

Looks like there might be a little bit of plastic coating here when we get the plastic coating out of the way, and again, I'm not really sure what to expect here.

Each cable is gonna be made a little bit differently.

It's a little plastic coating and there's some some stranded wire shielding that I'm just gonna pull back for now.

And then there appears to be some foil here is well, pull the foil back.

And then inside we find we find a few conductors, find a few a few wires here, and your USB cable might be construct a little bit differently.

You might have some different layers in here, um, but you should find you should find four wires inside, just as I have here, and there's a black red and then, uh, in this case, a green and a white.

But what we're interested in is the black and the red, because the black and the red are the positive and negative five volt source, and then the green and white are used for data.

If this USB we're plugged into a computer, then you might want to send data across it, and that's what these air used for.

I would definitely not use your computer to power our our experiment here because you could short something out and you know the worst case you could you could damage your computer, and you don't want to do that.

So definitely Only if you're gonna do this only power through one of these little wall adapters.

Because the worst case is you might damage the wall adapter, but this is relatively inexpensive.

Um, you don't want to risk damaging your computer.

So with that out of the way, Um, basically, the next thing to do is just kind of get all this shielding out of the way.

And I'm just gonna kind of get it all together here and cut it off because you don't want any of this.

This is they just put this in here to prevent, um, to prevent interference with the data signals.

And like I said, the you're interested in the in the red and the black because that's where the five old power is.

The other conductors that air in here, we can actually just cut him off because we're not using them.

And so I'm I'm left with the red in the black, and I could get clean this up a little bit more.