Circuit Theory

An LED is an electronic part that emits light when properly wired in an electric circuit. The LED has positive and negative leads protruding through a plastic body, as shown in Figure 4-1. You can use the Arduino in electronic projects to operate multiple LEDs. Figure 4-3 shows two LEDs wired to the Arduino D13 pin. The Arduino output pins are capable of providing 40 mA (milliamperes) of electrical current, sufficient to turn on two LED circuits wired in parallel.

Figure 4-3. Two LED circuits wired in parallel to the Arduino D13 pin; the arrows indicate the LEDs are on