So as we discussed yesterday we still need at least one more component if we're going to make this LED of ours actually blink. And here it is: the inverter.
An inverter is a component that behaves like a typical 5-year old. It does the opposite of what you tell it.
If you tell it 1, it goes 0.
If you tell it 0, it goes 1.
Sounds weird? Well, no - not if you have a 5-year old. It sounds like another typical day.
But so far as our circuit is concerned this component is going to help you blink a light!
I remember our teacher in school told us that computers use only 1's and 0's.
He was not able to elaborate any more on that.
I don't think he understood what that meant.
Luckily, my dad knew!
He told me that 1's and 0's had many uses. In the binary counting system, you could use them to create any number you want, just by sequencing them correctly.
He also told me that in the field of electronics, 1's and 0's was about voltage.
Voltage, you might remember from Lesson 2, is a force that pushes the wire's 'marbles' through a circuit, thereby creating a current.
Recall also that voltage is always measured between two points. So when we say that a wire "has a voltage", it means that if we measure the voltage (with a multimeter) between a point on the wire and the minus of the battery, it will show a positive voltage.
My dad told me that a 1 was a wire with a voltage and that a 0 was a wire without a voltage.
He then showed me how, in electronic circuits, you can use something called 'logic gates' to do something with the 1's and 0's. The 'inverter' was one of the logic gates he taught me.
An 'inverter' inverts the input.
So if 1 is on the input to the inverter, 0 will be on the output.
If there is a voltage on the input to the inverter - that is, if there's some 'force' - then that's a '1'. The output will be a '0' - zero volts. No force, in other words.
And vice-versa. If there is no voltage on the input to the inverter - a '0' - there will be a voltage - a '1' - on the output.
That '1' by the way is know as 'HIGH' in inverter-speak. The zero - you'll be unsurprised to learn - is called 'LOW'.
Now that's a handy thing when wanting to blink a light.
What if you connect the inverter's output to the LED circuit from the last email?
Say, something like this?
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Here you have a circuit with a two-way switch. The left side of the switch is either connected to plus or minus.
By the way - even though you don't see it here - the inverter is always connected to plus and minus too. And this is how it's possible that it creates a 1 out of a 0.
But since all logic gates need connections to plus and minus, it's considered a given fact. So they're usually skipped to simplify the circuit diagram. Here's how we would draw the inverter with those connections:
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For those who are curious about how inverters are made - they're made using transistors. But we're not going to go into that in these first lessons.
Let's look at how the circuit works:
To begin with, the switch is "flipped off" so you have 0 on the input to the inverter. But the inverter makes that into a 1 on the output, so the LED lights up. When you flip the switch on, you get 1 on the inverter input, so the output becomes 0 and the LED turns off.
You'll get a circuit that turns on the light when the switch is flipped off, and it turns the light off when you flip the switch on.
Which is the opposite way of how it worked without the inverter.
Now, on its own that doesn't sound like a really useful circuit, does it? You either see a light that's on, or you see a light that's off. And that's it.
Whereas we want one that blinks.
So tomorrow I'm going to add a little magic to this circuit and show you some electronics cleverness that gets us what we want. It'll be with you in 24 hours - keep an eye out!
SUMMARY
So now you know that an inverter reverses whatever is on its input.
If there's a positive voltage at its input (also referred to as a '1' or 'HIGH'), it'll output no voltage at all (a '0' or 'LOW').
If there's no voltage at its input ('0' or 'LOW'), it will output a voltage ('1' or 'HIGH').
It does the opposite of what you tell it - just like a naughty 5-year-old.
Keep On Soldering!
Oyvind @ build-electronic-circuits.com
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