Welcome back to my Electronics tutorial series. For those unfamiliar with this series, I give lessons discussing in detail how things work and how to test certain aspects of them. For those who are new, please see my first lesson and work up to here. For those who are not new, this lesson will be about how you can manipulate the flow of electricity in circuits. Also, from my previous lesson, I said the next lesson would be a coding lesson. Sorry, that is still in the making, but I wanted to equip my pupils with knowledge on more fundamental aspects of electricity before hand. But let's begin.
Step 1: Review: What Is a Circuit
For those not new, you should be familiar with this diagram of what a complete circuit is. But there is one thing that I made a mistake in this diagram: Assuming that the green connective wire directly carries power to the ground, this will cause a short circuit! Yeah, you remember those, alright. This short circuit would cause a normal battery to loose all its power in a few seconds. So to prevent this, we are going to have to find ways of regulating the flow of electricity through a circuit.
But first, let's go down to how electricity actually flows.
Step 2: The Flow of Electricity
In electricity, there are small, negatively charged particles called Electrons, labeled above. These electrons don't like to be close to one another, so when there is a spot that is positively charged (because there isn't as many Electrons there), the electrons want to go there. But in order to, they need a medium to get to the positive location. The medium of travel is called the conductor, which in the diagram is the wire. The conductor allows the electrons to move, generating electricity. The number of electrons moving per unit time (charge/sec) is called the current. Although this may be confusing, as it means that electrons come from ground, it also means that relative to the ground, the spots lacking electrons come from power. I will not go into too much detail, but simply remember that when looking at the flow from power to ground, you are really looking at the flow of holes where electrons should be.
Since it is the current that is causing a problem of short circuit, and no way to stop the current from crossing the terminals, how can we modulate the amount of current to get some work done?
Step 3: Manipulating Current
There are 3 main ways to or not to manipulate current (the movement of electrons). You can either:
Let it be and have no change done to it (shown as the regular current)
Reduce the amount of current flowing (shown in the second row)
Or supplement the circuit with extra electron flow (third row)
For each of the last two options, there is an associated device to accomplish the task. For reducing, the resistor comes in handy. And for increasing the current, there are two options, the transistor and the capacitor. Because transmitters have a variety of functions, we will not discuss them here (that is for another lesson).
Okay, okay, so you have the names of devices, but how do you use them?
Step 4: Using a Resistor
As I mentioned previously, the resistor is used for limiting current. This can be useful when you want to prevent something from frying. Take a look at the diagram to understand.
In the diagram where the resistor is not present, we see that the led is burning, unable to take the large current being given from its power source (the battery is there, but is represented as ground and power). However, when you insert a resistor into the circuit, the led shines without burning out. The reason: because the resistor is there to reduce the amount of current flowing through the circuit. There is a formula, called Ohm's law (after a German Physicist Ohm), that describes this phenomenon mathematically. Current = Voltage/Resistance.
So now you know how to reduce the current rushing into current sensitive devices (like the LED). But how do you increase the current to power high demand devices like motors? Enter the Capacitor!
Step 5: Using a Capacitor
Capacitors are interesting beasts, and can be confusing at times, so listen closely. How capacitors work is that they receive current from power (with a positive charge yes), but allows only a small amount of electric current to pass through the second terminal. What happens is that on the first terminal, the charge is being stored up like in a reservoir. What this allows is the ability to extract current from this reservoir into a separate circuit to power high consuming devices like the motor seen above.
Starting a motor requires higher current than running it in motion (like "overcoming inertia"). In the circuit without a capacitor above, we see that the motor is in a complete circuit, but is not moving (because of this "inertia"). This is because the current running is not enough to initiate motion. But in the circuit with a capacitor, the motor is receiving larger current levels from the reservoir to give the motor a better ability to start (initiate) motion.
But here is what is interesting about the circuit. Unlike the circuit with a resistor, the capacitor and motor are not connected in series, where one comes after the other. Instead, they are in what is called a parallel circuit, Where, technically, two complete circuits are made. Both share the same terminals of ground and power, but since the power's charge is being stored up by the capacitor, that charge is being given to the motor on the second circuit where it can start and move with the healthy current that it needs.
Step 6: Variable Resistors
You know how to restrict current and to supplement current. But what if you want to vary the level of current being restricted in your circuit? What if you want a dim light at one point and a bright light at another, and maybe want something in between yet another time? The potentiometer allows you to do this.
What you may notice first is that unlike the other devices I have shown you, the potentiometer has three terminals! Like the rest, two are for power and ground, represented in red and blue, respectively. But the third inner terminal is called input. What you will learn in future lessons is that this is the standard design of a whole family of electrical devices called sensors. But for now, lets see how this device works.
In the exterior design picture of a poteniometer, you see the three terminals, and you see a long spining apendage called the wiper. This wiper turns around in place, which, depending on its angular position, controls the level of resistance that passes through it. Looking on the inside, you may notice that through the resistive material ( the actual variable resistor), ground and power are connected. Fortunately, the resistor in between them is so high in resistance, that little to no current passes through it at that length. The wiper, however, is free to rotate its hand to any point on the resistor, which, because of its length, affects how much current passes.
In short, the shorter the piece of resistor that connects the power to the input terminal, through the wiper, the less resitance current experiences because the electricity has less resistive wire to go through. The longer the connection is, however, means the lower the current level. Now lets see how you would use this in a circuit.
Step 7: Using a Potentiometer
In the diagram above, you can see a potentiometer in the circuit. The idea of this circuit is to allow you to control the brightness of the LED. Try constructing this circuit to give yourself an idea of how to use a potentiometer.
To build it, you will first need:
-A power Source (a battery)
Take the power of the battery and connect it to the power end of the potentiometer. Then connect the potentiometer's ground (the second outermost terminal) and connect it to the battery's ground. This gives you a complete circuit as is. But, it won't do anything.
Next, connect the inner terminal of the Potentiometer to the long leg of the LED. From there, Connect the LED's short leg to the battery Ground. Now you have a second complete circuit. Try it out by swiveling the potentiometer and see the LED glow and dim as you turn it! Congratulations
What you may notice, when looking at this circuit conceptually is that it is very similar to the circuit design used with a Capacitor! And you are correct! This circuit design incorporates parallel circuits. The potentiometer's inner mechanism is inputing a certain amount of current to the LED through the input pin (the inner terminal), causing the LED's brightness fluctuate as you swivel the potentiometer.
Step 8: And NOW...
Well, I hope that you enjoyed this lesson in basic Electronics. What I hope you now know is that there are many new ways to regulate the flow of electricity and to manage it so it can give you the power and control you need.
Next time, I will be going into the basics of arduino coding.
Saddle up! It's gonna be a big one!
Until Next time.