Fundamentals of Electronics: Circuits, Components, and Arduino

A Circuit

A circuit is an unbroken loop of conductive material that allows electrons to flow through continuously without beginning or end. If a circuit is ”broken,” that means its conductive elements no longer form a complete path, and continuous electron flow cannot occur in it. The location of a break in a circuit is irrelevant to its inability to sustain continuous electron flow. Any break anywhere in a circuit prevents electron flow throughout the circuit.

A Fuse

A fuse element acts as a sacrificial device to provide overcurrent protection. Most fuses include a metal wire or strip that melts when too much current flows, which interrupts the circuit in which it is connected.

Electromotive Force (EMF)

To move electrons in a conductor in a particular direction requires some work or energy transfer. This work is performed by an electromotive force (EMF) typically represented as a battery. EMF is known as voltage or potential difference. Keep in mind that electric current is always through an element and that electric voltage is always across the element or between two points.

Variable Resistors

Variable resistors provide a range of resistance values controlled by a mechanical screw, knob, or linear slide. The most common type is called a potentiometer, or pot. A potentiometer that is included in a circuit to adjust (trim) the resistance in the circuit is called a trim pot.

Direct Current (DC)

Direct Current (DC) does not flow through a capacitor. Charges are displaced from one side of the capacitor through the conducting circuit to the other side, establishing the electric field. The displacement of charge is called displacement current since current appears to flow momentarily through the device. During the flow of displacement current:

• Capacitor charge increasing
  
  Capacitor is charging
• Capacitor charge decreasing
  
  Capacitor is discharging

Diodes

A diode can operate in two states:

• Forward biased: short circuit i > 0, v = 0
• Reverse biased: open circuit i = 0, v < 0

In the real world, there usually is a voltage drop when diodes are forward biased. In electric motors and relays, there are inductors with sometimes large currents flowing through them.

Flyback Diodes

The solution is to use diodes that absorb the inductor’s current so it does not have to sharply drop to zero when disconnected.

MOSFET

MOSFET= Metal-Oxide-Semiconductor Field-Effect Transistor

Similar to BJTs, they are 3-terminal devices and operate by controlling the current between two terminals using a voltage applied to a third terminal.

The terminals:

• Gate is the control electrode, analogous to the base of the BJT. It draws no direct current (DC) because it is insulated from the other terminals.
• Drain is analogous to the BJT collector.
• Source is analogous to the BJT emitter.

Why Arduino?

It is Open Source, both in terms of Hardware and Software. It is relatively cheap. It can communicate with a computer via a serial connection over USB. It can be powered from USB or standalone DC power.

Arduino Features

• Digital I/O pins 0—13
• Analog Reference
• Third GND pin (digital ground)
• LED connected to pin 13
• Pins 3, 5, 6, 9, 10, 11: PWM outputs varying from 0 to 255
• Pins 0 and 1: Serial communication (Receive and Transmit)

Analog Inputs A0-A5

Connected to outputs of a 10-bit analog-to-digital converter (ADC). A value between 0 and 1023 (2¹⁰-1) is read from an analog input. By default, 0 V is mapped to a zero reading and 5 V is mapped to 1023. Instead of 5 V, the maximum voltage can be set by a command to be 1.1 V or the voltage connected to AREF.

Examples:

• Value read = 512 ⇒ Voltage input = 2.5 V
• Value read = 256 ⇒ Voltage input = 1.25 V

Arduino Sketches

Arduino files are called “sketches”. Arduino sketches must be compiled in the IDE before being downloaded to the Arduino board. Two required functions in an Arduino sketch are setup() and loop().