Name: 7セグメント16進デコーダの設計 (Designing a 7-segment hex decoder)
Uploaded: 2021-01-14T10:13:59.000Z
Duration: 15 min 33 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：

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So if we want to build some kind of output display for a computer, we can use a register just like we've built in the past, where we can push a value into that register and then have some way of displaying the contents of the register.

And this would be the output of the computer.

You can see we have a nice binary output for for the computer, but would be much nicer is if when we put contents into that register instead of getting a binary output, we get a nice decimal output like this, which is much more user friendly.

Let's take a look at how these display modules work so you can see there's some pins on the back.

And here's the data sheet that comes with it, or I guess, just sort of the packaging, and it comes in a couple different kinds.

The one that I have is blue, and it says common in owed.

What that means is that there's a bunch of ladies inside this package for each of these different segments and all of the anode they're tied together, says the positive side of the of each of these ladies are tied together and on pins three and eight.

This is pin three and then this is pin eight here in the middle on the other side.

And then the rest of the pins just control the different segments.

We could hook this up on our bread board, and I'm gonna connect the anode.

This is the common anode, which is either pin three or pin eight to our five whole supply.

We're gonna connect that with a 100 ohm resistor.

So it's gotta three volt forward voltage.

Which means that the resistor needs to drop two volts is three plus two is five on.

I'm guessing it doesn't actually tell me the current draw on this thing, but I'm guessing 20 millions would be good.

So 100 ohm resistor should should work fine.

I'll connect power noses, this five volts, and if we connect ground any of these other pins, we should see stuff light up.

So this is that first segment second segment third segment for 1/5 sixth and this is the middle segment.

And then down here is also the decimal point.

And so you can see the inputs to this thing.

Don't really let us input numbers per se.

There's not a binary input that just then displays a number.

We have to display numbers sort of on our own by lighting up just the right segments.

So if we want to light up the number one, we have to connect those two segments.

If we want to dio the number two, then we have to find all all the right segments for number two.

It's it's probably this one and then this one down here and then finally this bottom one.

And that's how you get the number two is we have to have to manually know exactly which segments delight up to get each number.

But of course we have a binary number that we want to display.

So a good approach when you don't know how to solve a problem is to try to simplify the problem on Dhe try to solve that simpler problem.

So in this case, let's let's try to solve this problem, for we only have four bits.

So instead of thinking about eight bits and how we display that with three digits, let's think about how we display four bits.

This is essentially what we want to display for each of these bits, you know, zero through nine, and then when we get above 9 to 10 instead of trying to display, that is two digits weaken.

Those as letters on this would basically just give us a hex decimal display.

So instead of 10 11 12 and so forth, we have a, B, C, D, E and F and half represents 15.

So this gives us ah different different display for each of the 16 values that you can have with four digits of binary.

So these are all the different numbers, or I guess, digits or things we want to display.

Um, and we can create a truth table that looks at each of those cases and to simplify things even further.

What we can do is actually just look at a single segment in each of these and try to solve each segment by itself.

It's instead of looking at the whole number, let's just look at one segment.

In fact, we'll start with this segment on the top here, and what you'll notice is that for any of these segments we can control whether it's on or off by setting the pin for that segment to either five volts, which case it's off or ground which case it's on.

And and that's because these are these common anode.

Um, if I had the common cathode one that it would be the other way around on, you could use the same sort of logic.

But since these are the ones I have, we'll do it this way.

And so basically, if this input is is ground or a zero, a logic zero, then that segment is on.

If that pain is a logic one or five volts, then that segments off because you've got five volts on both sides of that led, and so there's no current flowing.

So with that in mind, we can come up with a truth table for that segment.

Each of these segments kind of by convention, has a letter associated with it.

So if we look at just that segment, we can see well for zero, it's on.

Because we want that segment to be on, which means we want the input for it to be at ground or zero, and that turns it on for one.

It's off So that the one for two, it's on that zero for three.

And so what we've got here is a truth table that says, if you have these inputs, we want that output.

If you have these imports, we want that output.

And so now the question becomes, what can we build a circuit that satisfies this truth table, some kind of logic circuit, And if we could do that, then that gives us the logic required to tell us when we should turn on that top segment and then we could do the same thing for the rest of the segments.

So here's the circuit that I came up with.

And so what you can see is we've got the imports d zero d one d to Andy three, which correspond, or for a bit binary number that's coming in.

Those four imports is desire ready 12 and three and then I'm also inverted all of them.

So we also have the compliment of D zero d one d to Andy three over here.

And then what I'm doing is using a combination of and Gates and or Gates to decide whether this final output should be a one or a zero.

And the way that I did this is by looking down this column here at our outputs and looking at, Well, when do we want our output to be one?

And it turns out there's only four times that we actually want our output to be one.

We wanted to be one here, here, here and here.

And so if you look at just one of those cases when the outputs are one, the inputs are one are 0001 And so that's actually what thes three n gates do here.

Three n Gates is as a four input and gate.

I'm just using to input and gates for because it's what I have.

But what you see is I'm taking I'm handing together D zero.

So when d zero is one like this when d one d to Andy three are all zeros because if they're zeroes than the compliment of them will be ones.

And then all four of these inputs will be one.

And if all four of those inputs Air One than both of these outputs, where one and this output is one, and then that output there get sword together with the rest of the stuff, um, and and will eventually turn the final output on this A which of course, means that that input will be a one and the segment will be off just like it should be for the number one that top segments not on in number one.

Same thing for for here this is ah, the number four.

So the number four D two is high, but D zero D one and three are low.

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7セグメント16進デコーダの設計 (Designing a 7-segment hex decoder)

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