The Arduino Anatomy, The Signals, The Sensors & The Actuators

Now we know that Arduino is an open source platform, this means that all the information regarding the hardware and software provided is freely available and can be used by anyone. And it also means that the learning is possible for us now… possible even if we have no basic in electronics or hardcore engineering knowledge. What we need now is a dedication to learn it.

Let’s focus on our main topic here, getting started with Arduino. Imagine if you already have any Arduino board, be it Arduino Uno, or Nano, or Duemilanove, or maybe Mega 2560, the first thing you should do is study the hardware.

So, before we go deep into our discussion here, let us go through the outline of this article, what we aim to understand by the end of this article:

• Exploring The Basic Anatomy of An Arduino Board
• The Electronic Signals
• Sensors and Actuators

Since its introduction in 2005 up till today, Arduino has released hundreds of hardware designs in many shapes and forms. Even all Arduino boards might be different from each other, however, there are some elements that can be related on practically in any Arduino. Therefore, in this section particularly, we will use Arduino Uno as an example ^[1].

• 1. USB Port

  This port is used to connect the Arduino board to a computer.

• 2. USB to Serial Chip

  This is an important component that helps translating the data that comes from the external machine, such as a computer to the on-board microcontroller. It also allows us to program the Arduino board from our computer.

• 3. Digital Pins

  These are the pins that use digital logic, usually for controlling the switches or turning on/off an LED. For reference, digital logic is the numerical representation of the signals and patterns in a digital circuit like ON/OFF or HIGH/LOW.

• 4. Microcontroller

  This is the main processor of an Arduino. This is the component that we load our programs into. You can imagine it as a little computer, but created to do only a specific number of things.

• 5. Analog Pins

  These are the pins are used for reading analog values in a 10 bit resolution (0-1023).

• 6. VIN

  VIN - stands for Voltage In. It is a power pin with a dual function. This pin can work as a voltage input for regulated external power supplies that do not use a barrel jack connector.

• 7. GND

  Short for 'Ground'. It is also known as negative or simply ‘-‘, is used to complete a circuit, where the electrical level is at 0 volt.

• 8. 5V

  This pin outputs a regulated 5V from the regulator on the board. It can supply maximum about 800 mA of current.

• 9. 3.3V

  You can use the 3.3V pin to power sensors and modules that need 3.3V power. It can supply about 100 to 150mA of current.

#1-Analog Signals

An analog signal is a signal that represents data as continuously. Example of analog signal can be seen in the displayed figure. Among the application that use analog signal are speech recording, voice filtering, and sound controlling.

An analog signal is generally bound to a range. In an Arduino, that range is typically 0-5V, or 0-3.3V. If we for example use a potentiometer (an analog component used to change the resistance of a circuit), we can manually adjust this range (0-5V). In the program, this is represented in a range of 0-1023, which is a 10-bit resolution.

#2 – Digital Signal

A digital signal is a signal that represents data as a sequence of discrete values. It works a bit different, representing only two binary states (0 or 1) that are read as high or low states in the program. This is the most common signal type in modern technology. Example of digital signals can be seen in figure below. When the signal is ‘1’, the bulb will turn on. When the signal is ‘0’, the bulb is turn off.

#3 – Pulse Width Modulation (PWM)

It is hard to understand PWM if you heard it for the first time, but as soon as you are familiar with this term, it will become easier for you to understand how this thing works. Just imagine a bulb that is lighting up, on an off alternately, it can be represented as a digital signal. But what if the bulb is lighting up gradually? This is where PWM is needed.

PWM is a way to control analog devices with a digital output. Take a bulb for an instance, lighting up a bulb gradually seems like we are controlling the input voltage to the bulb using an analog signal. Truthfully, it is not analog signal that we feed the bulb, but it is PWM. We can change the proportion of time the signal is high compared to when it is low over a consistent time interval.

In PWM, there are two main components that determine its behavior which are frequency and duty cycle.

• Frequency – determines how fast PWM completes a cycle.
• Duty cycle – determines the amount of time the signal is ON as a percentage of the total time of a cycle.

Observe figure ‎above, that shows the different percentage of duty cycle. We can see how the difference in percentage of the duty cycle will influence the brightness of the bulb.

The Arduino that we use support PWM signals. If you observe carefully on the Arduino UNO board, there are tilde symbol (‘~’) among the digital pins displayed as highlighted in figure ‎shown ^[2]. This symbol means that the digital pin support PWM signals. Therefore, if let say you have a project that require you to control the brightness of an LED, you can use any digital pins that has tilde symbol.

Before you begin experimenting with something with Arduino, you need to know what type of electronic devices you are playing with. Either it is a sensor, or it is an actuator. In this section, we will discuss these two elements: Sensors and Actuators.

What is a sensor? A sensor is a device that measures physical input from its environment and converts it into data that can be interpreted by either a human or a machine ^[3]. We may come across various types of sensors frequently in our daily lives, for instance, the thermometer (temperature sensor), automatic door opener system (PIR sensor), or car reverse sensor (ultrasonic proximity sensor).

In Arduino, sensors can also take the form of just a simple button: when a state change (we pressed a button), the electronic signal is switched from low to high (0 to 1).

Meanwhile, an actuator is a part of a device or machine that helps it to achieve physical movements by converting energy. Simply to say, the actuator is the component in any machine that enables movement ^[4].

How actuators are controlled depends on what type of component we have. The simplest way is to simply turn something on/off, while the more advanced is controlling the amount of voltage a component receives (i.e. the speed of a motor).

In brief, sensors, and actuators, are typically referred to as inputs and outputs. When we write a program, it is common to construct conditionals that check the state of a sensor and decides whether it should actuate something.