Name: トラブルシューティング。LEDが薄暗い理由の調査 (10のうち5) (Troubleshooting: Investigating why the LED is so dim (5 of 10))
Uploaded: 2021-01-14T10:15:56.000Z
Duration: 5 min 43 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

過去完了形

So the last video we had connected up these two different circuits, one that had a five volts signal that switching on and off coming from some other circuit and the other that had five volts coming from just a regular power supply.

And for some reason, the five volts coming from this power supply is is making this led much brighter than the five volts that's coming from the signal.

法助動詞 B1

And we were a little bit puzzled as to why that might be because we measured both of these and and when we measure the voltage coming into this top circuit we saw we had five volts when When it when it was on, we'd have five volts and the bottom one.

We have five volts and we looked at the resistors.

The resisters air the same, but for some reason, the eh ladies are not the same brightness when when they're both on.

And so if voltage is the same and resistance is the same, the next thing to kind of check out might be might be Ah, the current.

How many amps are actually flowing through this circuit?

And so we can do that with our multi meter we can We can go ahead and set it to measure amps, and I need to move the power lead over here.

And so what we have to do to measure amps is actually put the meter in Siri's with circuit.

So what I'll actually do is take the led out of the circuit out of both of these circuits and I'll put the AM eater in place of where the led iwas just to see how many amps were flowing through that part of the circuit where the led iwas.

And what we see is that we either get about zero amps or it looks like almost 00.3 million amps.

So when this is all in, we get 0.3 millions.

When it's off, we get zero, and it just seems to be switching back and forth between those two, which is which is what we expect.

We'd expected to switch back and forth between zero and some number of of milli amps, so it switching back for 30 and 300.3 millions.

Now it's come down here and see how many amps air flowing through this part of the circuit where this brighter led iwas.

And here we see 23 million amps is ah is almost 100 times the amount of current that was flowing through the top circuit when it was on.

So we have 23 millions here and the top circuit.

And so that that right, there is basically the explanation of why the led on the top circuit was so much less bright than the led in the bottom circuit.

The resistance is the same, but the current is almost 100 times less, and so the led is much less bright.

Um and so the question is, what can we do about this?

We have plenty of current because this is a power supply, and power supplies are generally designed to be able to deliver a lot of current and maintain their voltage.

I mean, it's hard to say what what the signal is trying to do, but in this case, oftentimes a signal will Will will indicate you know, whether it's offer on with a voltage.

But it may or may not allow you to draw a ton of current from it.

So power supplies designed to let you draw a ton of current you know, a signal like this might not necessarily so again, if we go back and look at the voltage here when this is on, we're definitely getting, you know, over five volts.

So the signal is, is using that five volt potential t indicate whether it's on or off.

So if I see five volts, then that's telling me this signal is saying on if I see zero votes to signal saying off.

But when I try to connect, any kind of load like this led to the signal the led tries to draw, you know he needs to draw some current in orderto light up.

It wants to draw 20 millions ideally, but there isn't 20 million amps available.

You know this this signal just can't provide 20 million pes it can only provide, you know, almost 1/100 of that.

And so the led ends up not being very bright.

And when the led does draw that much current relative to what this can provide, this can't even maintain the five volts anymore.

And that's why we see the voltage is so much less so.

The question is, how can we used this voltage differential somehow?

Detect that there's a voltage change there and still get current through the led.

Um, and the answer to that is an ingenious little component called the Transistor, which you probably heard of.

And I have some transistors here, these air transistors, and hopefully you can see him down there.

So these air transistors and basically a transistor, um, can be thought of in a couple of days.

It could be thought of as a switch or a current amplifier.

If that doesn't make sense in the next video, we'll go through how we can use a transistor basically, too.

At least if we get the led out of the way, it'll be five volts.

That's turning on and off and use that to switch in, led on and off and have the led be bright And have this five old signal not be not being strained, not be dropping so much by putting the led right right in the circuit.

So we're gonna use transistors to do that.

 And in the next video, we'll talk about how, um, how the transistor is gonna help us do that, and then we'll build it and and see if we can get it to work. 