## Introduction: Prerequisites

*The following information is a single lesson in a larger project. Find more great projects *here*.*

**Return to Previous Lesson: **Build a Simple Circuit (Simulator)

**Lesson Overview:**

Now we'll learn what we'll need to do before jumping into the full kit!

## Step 1: Introduction

Before starting the Arduino Basic Kit projects, it is helpful to have some foundational knowledge of electronics!

The following topics are not required for completing projects, but they are highly recommended. We'll go over some of the basics in this lesson and also provide links for more information.

- Continue to the next step.

## Step 2: Current, Voltage and Resistance

In order to talk about electrical circuits, you need to be familiar with the terms voltage, current, and resistance. These terms are defined below.

For more information:

Refer to the Arduino Get to Know Your Tools project.

- Current (measured in amperes, or amps; with the A symbol) is the amount of electrical charge flowing through a specific point in your circuit.
- Voltage (measured in volts; with the V symbol) is the difference in energy across one point in a circuit and another.
- Resistance (measured in ohms; with the Ω symbol) is how much a component impedes the flow of electrical energy.
- Continue to the next step.

## Step 3: Ohm's Law

Current, voltage, and resistance are all related to each other in an electrical circuit. When you change one of these in a circuit, it affects the others. The relationship between them is known as Ohm's Law, named for Georg Simon Ohm, who discovered it.

Ohm's Law applies to the voltage of, current through, and resistance of a single component - such as a resistor.

VOLTAGE (V) = CURRENT (I) x RESISTANCE (R)

For more information:

Refer to the Arduino Get to Know Your Tools project.

- Continue to the next step.

## Step 4: Circuit Diagrams

In this project, you have seen circuits laid out on a breadboard or real components connected to each other with wires. In future projects we will also be using circuit diagrams, which use symbols to represent components.

A circuit diagram is like a flowchart for your circuit, giving you a map of which components are connected to each other.

The component symbols that we use in the Arduino Basic Kit projects are shown in the chart below.

- Many of the circuit diagrams symbols look like the components they represent. For example, the symbol for a piezo speaker looks like a loudspeaker cone!
- Continue to the next step.

## Step 5: Voltage Dividers (1)

It is useful to know a few things about voltage dividers before embarking on projects that use analog sensors. The voltage divider that we use is simply two resistors in series between high and low voltage points. The resistors share the total voltage and you can create a custom voltage level between the two resistors by changing their values.

To figure out what the voltage is over each resistor, you use the following system of equations, considering the fact that the current flowing through each resistor is the same!

I = V1/R1 = V2/R2

V1 + V2 = total Voltage = 5 V

The voltage that you usually care about is the output (V-out), which is equal to V2.

V-out = V2 = (5 x R2) / (R1 + R2)

For more information, and the full derivation of the voltage divider equation, visit:

https://en.wikipedia.org/wiki/Voltage_divider

- As a general rule, the larger resistor in a voltage divider will have the larger voltage across it!
- Continue to the next step to see an application of voltage dividers.

## Step 6: Voltage Dividers (2)

Voltage dividers are used in many projects with analog sensors. The light sensor, for example, changes its resistance when light is shining on it. Under low light conditions, the sensor is 180 k-ohms. Under bright lights, it is 506 ohms.

Instead of detecting resistance directly, the Arduino needs to sense a voltage. We use the voltage divider shown below to convert the resistance into an output voltage signal.

- In the light sensor example, if the sensor is hit by medium-level light and has a resistance of 1000 ohms, the output voltage that reaches the Arduino board will be 4.5 volts.
- As a general rule when more light hits the sensor, its resistance decreases and the output voltage in this circuit increases.
- Continue to the next step.

## Step 7: Multimeter (recommended)

Finally, a multimeter is a useful tool for that can verify the amount of resistance of a component, thevoltage across a component, or the amount of current running through your circuit.

There is a multimeter available in the circuit simulator. For more information on using it to measure current, you can visit the following Project Ignite video tutorial:

- In the light sensor example, if the sensor is hit by medium-level light and has a resistance of 1000 ohms, the output voltage that reaches the Arduino board will be 4.5 volts.
- As a general rule when more light hits the sensor, its resistance decreases and the output voltage in this circuit increases.
- Continue to the next step.

## Step 8: Review

Once you have reinforced your general knowledge of the prerequisites, you can continue on to create cool projects with your Arduino!

The instructions for each project will provide you with enough information to complete it, even if your electronics foundation is a little rusty. However, be sure to look out for the following terms, and review the concepts when needed:

Current

Voltage

Resistance

Ohm's Law

Circuit diagram

Voltage divider

Multimeter

Let's get started with the next project: Getting to know your tools!

Congratulations, you have completed this project!

Check out other great projects here.

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