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• So oftentimes, in electronics, we find ourselves interfacing with with other circuits.

• Um, and I have an example of another circuit here, and this is this is some other circuit that I built that I'm actually not gonna talk too much about what it does.

• So I'm gonna I'm gonna kind of push it aside over here so that we're not looking at it.

• Um, because, like I said, oftentimes, electronics, we find ourselves interfacing with other circuits like that that we don't know all the details of exactly how they work, and we don't really want it.

• We don't even need to know all the details in order to interface with them.

• You know, like, if I want to build something that plugs into a computer, um, I don't need to know all the details of of the circuitry inside that computer.

• I really just need to know what the signal is that it's sending me and how to interpret that signal.

• And so I have this circuit here it is sending me some sort of signal across thes across these two wires.

• Um, and I want to look at what that signal is and see if we can do something interesting.

• So I have a volt meter here so we can start by just looking at the voltage across these these two wires to see what's going on.

• And if we take a look at the volt meter, we see something kind of interesting here.

• It seems like this is switching between zero volts and ah, little over five volts, zero volts, five volts, zero volts, five volts.

• And so it looks like the signal that I'm being sent.

• It is either zero vaulter five olds.

• Um, and I happen to know since I built that circuit, that that's exactly what it's supposed to be doing.

• It supposed to be just switching between those two.

• Those two voltages.

• Um, so that's interesting.

• So I have ah, having led here.

• So maybe we can Maybe we can use this led on and hook it up in some way to this signal in so that the led turns on and off when the signal switches between zero and five volts.

• So I'll get this out of the way.

• And, of course, when it's when it's a deer revolts, that that's pretty easy.

• The led is gonna be off.

• Um, went to five volts.

• Well, we've kind of already looked at how to hook in, led up to a five old source.

• And so we found that we needed a resistor of some sort and so I haven't led and resistor, So we should be able to hook the resister in the led up to this.

• And, um, when this signal is zero votes, the led should be off.

• And if we hook it up right when the signals at five volts, the led will turn on.

• So we should actually be able to get the led to flash on and off by By using this signal, so have the resistor here.

• This is a 220 ohm resistor, which is the same one we used before When we when we calculated how, how big of a resister we needed to hook and led up to five volts and I have course the led.

• So we'll hook.

• We'll hook all this up and so we have the negative, the electrons, of course, air flowing in the negative side here, through the resistor, through the led.

• And then out the positive side here and we see the led flashing on and off.

• And in case you don't see that, I'll turn the lights off and you should see the led is flashing on and off.

• So when the circuit is sending us five or when this signal is sending us five volts, we see the led.

• Come on.

• When it zero votes, we see the led go off.

• And so it's flashing on and off like that.

• But one thing that seems kind of, um, a little bit mysterious here is that for some reason, it looks like the led is not as bright as it was when we just had it hooked up to five volts before.

• So I don't know if I'm just imagining that or what's going on, but just just to double check that, um, we have this this five volt Ah, this five, A little, uh, USB adapter thing that we modified so that we could we could get five bolts out of it.

• And so I'm gonna go ahead and just actually hook up on almost identical circuit down here with another resistor, and another led.

• So we'll hook my five volt source into just right below here into the into the bread board and Well, go ahead and get another resistor.

• And this is the exact same sort of resister.

• This is Ah, 220 ohm resistor and we'll get the exact same sort of led.

• This is the same yellow led that we've been using.

• Um, so we'll plug that in right here.

• So this is the same circuit that we have up here.

• It's just that now, instead of this sort of mystery five old signal that's turning on and off coming in here we have the five volts from from this from this power adapter from this little USB adapter that gives us five volts.

• So we'll go ahead and plug this in and the led comes on and definitely right away.

• You notice that this bottom led is much brighter, especially if I turn the lights off.

• You can see the bottom led is just, you know, really a lot brighter than the top one.

• When when the top one is on, Of course.

• So So what's going on here?

• Let's let's see if we can do a little a little detective work here and find out what might be what might be the difference.

• So let me get my voltage, My my meter probe here.

• So I'm gonna take the ladies out for a moment and just measure things.

• So this bottom, we think, is five volts.

• So let me just double check.

• And sure enough, it's 5.1 a little over 5.1 volts, and I'm going to go to the top and just compare and see what's going on up here and up here.

• It's either zero or a little more than 5.1.

• So when it's on, it's it's the same voltage.

• And of course we've got the same the same resistors here, too.

• And just to double check, I mean, who knows?

• Maybe these resistors air are kind of weird.

• We can actually measure the resisters as well.

• So you know the bottom one here is 217.6 homes, and it's a 220 ohm resistors.

• So I guess that's because that's close enough.

• And the top one we can measure this resistor 217.7 homes, So the resisters air the same uh, basically the same.

• The voltage is the same.

• The ladies of the same, eh?

• So So what's going on?

• Um, you know, down here, just double check this again.

• Go back to our voltage reading 5.1 volts.

• Connect our led in here.

• That comes on nice and great.

• Um, we could just double check all of our other voltages here.

• So the resistor is dropping 3.1 volts.

• The led here is taking almost two votes, which is which is right, what it should be taking.

• So, of course, this bottom one looks okay.

• Let's see if we see those same things on the top one.

• So I'll plug in here and just to see.

• Yep.

• We're still getting the 5.1 volts when when it's on.

• So connect the led and the led starts flashing.

• But something interesting is going on here.

• You notice Now the voltage is only going upto 1.8 volts.

• And when I had the led out of there, we take the led out.

• It goes up to 5.1 volts.

• When I put the led back in the voltage only goes up to 1.8 balls.

• No, not changing anything with the With the circuit that's sending us this signal.

• It's only just when I add the led.

• For some reason, um, we're not getting the same amount of voltage on the signal when I put that led in the circuit.

• So that's that's kind of curious.

• Um, so that might be a clue as to what's what's going on here.

• But I'm actually gonna end the video here because I want you to think about what might be the difference between the five volt power source with the bottom and this five old signal at the top.

• You know, both of these, you know, we measured are giving us five volts.

• But what might be different about the power that we're getting from this five volts versus the power we're getting from this five volts.

• See if you can come up with any, um, any hypotheses of your own, and then we'll we'll dive into this a little bit more in the next video.

So oftentimes, in electronics, we find ourselves interfacing with with other circuits.

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B1 led signal resistor circuit voltage hook

# Connecting to a mystery signal | Digital electronics (4 of 10)

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林宜悉 posted on 2020/03/27
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