## Off to the races: debugging!

What are voltage, current and resistance? How are they related? And why should I care?

In this chapter, you will learn about voltage, current and resistance and how they interact with each other. This will help you understand how your circuits are working, and how to make adjustments to them. We will also learn how to use the multimeter to measure these properties. This will aid in debugging your circuits and also get you on your way to designing and building your own projects from scratch.

### Understanding electricity

Electricity is the flow of electrons through a material. In the projects in this book, electrons flow through carefully arranged and specified paths: our circuits.

Electricity has three main properties: Voltage, Current and Resistance. In this chapter, we will see how these properties interact with each other, in a fundamental relationship called Ohm’s Law. We will also learn how placing components in different arrangements affect the electrical properties in a circuit.

Why are we looking at electrical properties, and not just building more circuits with our Arduino and other components? If you don’t understand a bit about how these properties work in a circuit, it will be very difficult to move on to building your own circuits after we’ve completed all the projects in this book. Also, without some understanding of these properties, troubleshooting your projects is next to impossible. In this chapter, you will learn more techniques for debugging your projects.

#### Measuring electrical properties with your multimeter

Remember the multimeter from Chapter 2? We learned how to set it up to test for continuity (whether our components are connected to each other). The multimeter helps us to debug problems in a circuit. By testing for continuity, for example, we can verify that our circuit is a complete loop. In this chapter, we will learn how to use our multimeter to measure voltage, current and resistance. Why do we need to do this? Testing voltage and current will help us analyze problems with our circuits; for example, is our circuit getting voltage? How much voltage is each of our components consuming?

Understanding how voltage, current and resistance interact in a circuit helps us troubleshoot our projects as well as build new circuits.

If we are going to use our multimeter to test electrical properties in a circuit, we will first need to build a circuit. We will start with a basic circuit that contains one LED, a resistor, a breadboard and an Arduino. We are not going to write an Arduino sketch this time; we will instead simply use the Arduino as a power source. We will check the voltage coming out of the Arduino, then the voltage across each component. We will then add a second LED to the breadboard and see how the electrical properties of the components depending on if we place them in a series or in a parallel arrangement. We’ll explain exactly what we mean by all of this shortly.