So yesterday we connected our LED into our circuit.
Here's what our drab, grey circuit now looks like with the battery, the switch and the LED added:
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And then we switched it on and - kaboom! - it exploded!
(Okay, maybe it wasn't that dramatic - but at least we broke it...)
It happened because there was too much 'current' flowing.
So we're going to add a special component to make sure this doesn't happen.
That component is a resistor.
But first - what is 'current'?
Imagine that the wire and components in our circuit are completely filled with marbles. When you switch on the circuit, the marbles move around the circuit from one side of the battery and back in through the other side.
There's no extra room - the circuit is completely filled with marbles - so when one marble goes out from the battery and into the circuit, another one is pushed back into battery on the other side.
And all the marbles must, therefore, move with the same speed.
The speed of the marbles represents the size of the 'current'.
These 'marbles' are pushed through the circuit by a force known as 'voltage'. The battery provides the voltage and is what creates the current.
When you know what current is, resistors are easy to understand:
A resistor is a component that *resists* current. It slows down the movement of the 'marbles'.
You can think of it as a tighter tube.
The more resistance, the slower the 'marbles' will go through the circuit. Unless you 'push harder', which means increasing the voltage.
We use resistors to control the current and/or the voltage in a circuit.
In our circuit, we will control how much current goes through the LED by introducing a resistor that reduces it.
So now we have a battery, a switch, an LED and a resistor. Here's our modified circuit diagram:
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In real life to test this circuit, you can use something called a breadboard. Breadboards make life easy when it comes to seeing if your circuit will actually work.
Check out the video below to see me connect a similar circuit on a breadboard:
https://youtu.be/uBGDME2pA_8
In most circuits, you'll have a lot of connection to plus and minus. So to simplify, we use symbols.
This symbol means to connect to plus:
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And this symbol means to connect to minus:
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Using these symbols, our circuit becomes:
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As we continue, we'll use these symbols instead of drawing the battery.
One more thing:
Many beginners try to understand a circuit by looking for a simple loop from plus to minus.
And that's understandable. After all, the word 'circuit' suggests that something comes out one side, goes around a loop and comes back in the other side.
Which it does.
But the route from one side to the other isn't always as straightforward as you might think.
Because the moment you go beyond a simple battery-plus-light bulb set-up, this happens: You'll find that within your nice, straightforward loop you have loops, sub-loops and even loops within sub-loops - not to mention sub-loops that change over time!
It's part of what makes electronics fascinating - and fun - but, of course, we still need a way to see the flow of current to be able to understand the circuit.
Do you know what professionals do?
We make life easy on ourselves.
We think of voltages, not loops.
And to find how the current flows in a circuit, we have a rule:
Current always flows from a higher voltage to a lower voltage - if there is a path for the current to take.
With this rule, we don't have to look at the current in the whole circuit to understand it. We can look at a small part, figure out the voltages, then see how the current flows in that part of the circuit. And if voltages between two points should change - which they sometimes do - then we can also see how that change affects our circuit.
That's so much easier!
With practice, you get better and better at spotting higher and lower voltage points - and so your circuit quickly makes sense.
So. We're doing well. Our circuit is underway.
But there's another ingredient we need to make this light blink. It's a strange thing... a kind of electronic disobedience.
Basically, whatever we tell it to do we want it to do the opposite.
Which is odd when we think about it... but it'll make sense when you see it in action tomorrow!
SUMMARY
You know that a resistor reduces the amount of current in a circuit, slowing its flow. And you also now realize that current doesn't flow in the same direction along the same paths at all times. It flows from higher voltage to lower and that those voltages can change from time to time - causing current to alter its path.
Keep On Soldering!
Oyvind @ build-electronic-circuits.com
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