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Welcome

This class is a two-session immersive introduction to digital electronics using the Arduino platform.
We'll learn how to use this microprocessor board to read digital and analog inputs, interface it to some sensors, and to high-current actuators like motors and relays (using transistors).

What is Arduino?

• Simple board that has everything necessary to program and run the Atmel ATMega 8-bit Microprocessor.
• Designed to work with an easy-to-use Arduino programming environment modeled on Processing.
• Features a serial-to-USB converter chip that enables data transfer & microprocessor programming over USB.
• Exposes all of microprocessors analog input and digital input/output pins.

Installation Instructions

arduino.cc/en/Guide/HomePage - click Mac OS X, Windows or Linux..

A Few Important Concepts

The terms we'll most often use in talking about electronics and electricity are Current (I), Voltage (V) and Resistance (R). Current is the flow of electrons through the wire of an electronic circuit. Voltage is the force that causes electrons to move and create current and Resistance is something that opposes the flow of current through a circuit.

Water analogy is helpful in understanding these concepts. The height of the water in a tank can be thought of as Voltage. The flow of water through the tube is Current. The crank that controls the flow is like a Resistor.

Fundamental law of electricity (Ohm's law) is that the Current is directly proportional to the applied Voltage:
V = IR

Basic Electronic Parts

Resistor is an electronic component designed to oppose an electric current. We can buy them with preset resistance
(Ohm) values indicated by colored stripes.

LED (light-emitting diode) is an electronic part that produces light. We can change the LED brightness by
setting the current that flows through it using a Resistor, according to Ohm's law.

Breadboard

Solderless, reusable prototyping board for assembling electronic circuits. Use holes within one column to connect
parts together. Top and bottom rows are interconnected across the whole board and used for Power and Ground.

The First Program

In Arduino environment, open File > Sketchbook > Examples > Digital > Blink

	int ledPin = 13;                // LED connected to digital pin 13

	void setup()                    // run once, when the sketch starts
	{
	  pinMode(ledPin, OUTPUT);      // sets the digital pin as output
	}

	void loop()                     // run over and over again
	{
	  digitalWrite(ledPin, HIGH);   // sets the LED on
	  delay(1000);                  // waits for a second
	  digitalWrite(ledPin, LOW);    // sets the LED off
	  delay(1000);                  // waits for a second
	}
	

Digital Input

We can use a Button or Switch as digital inputs to the microprocessor.

• Add inputPin variable and assign it as an input in setup.
• Add a new variable val that we'll use to store the input value.
• Add digitalRead function to get the input.
• Add an if .. else .. statement to make the LED turn on when input is high

	int ledPin = 13;                // LED connected to digital pin 13
	int inputPin = 2;               // connect digital inputs to this pin
	int  val;
	
	void setup()                    // run once, when the sketch starts
	{
	  pinMode(ledPin, OUTPUT);      // sets the digital pin as output
	  pinMode(ledPin, INPUT);       // sets the digital pin as input
	}

	void loop()                     // run over and over again
	{
	  val = digitalRead(inputPin);
	  
	  if(val == 1)
	    digitalWrite(ledPin, HIGH); 
	  else
	    digitalWrite(ledPin, LOW);

	  delay(1000);
	}
	

Analog Input

We'll use a Potentiometer as an input to our program.
Potentiometer is simply an adjustable Resistor. This is a part you can find behind a knob on your stereo. Instead of changing the volume of sound, we'll use it to change the brightness of an LED.

• Replace the digitalRead with analogRead function.
• Modify delays to make the LED bright when input value is high, dim when it is low.

	int ledPin = 13;                // LED connected to digital pin 13
	int inputPin = 2;               // connect analog inputs to this pin
	int  val;
	
	void setup()                    // run once, when the sketch starts
	{
	  pinMode(ledPin, OUTPUT);      // sets the digital pin as output
	}

	void loop()                     // run over and over again
	{
	  val = analogRead(inputPin);

	  digitalWrite(ledPin, HIGH);  
	  delay(val/50);
	  digitalWrite(ledPin, LOW);
	  delay((1023-val)/50);
	}
	

Communication

Let's get our microprocessor talking to the computer. We'll transmit the analog value of the potentiometer to the Arduino environment over USB.

• Add serial speed (baud) configuration in setup.
• Add print function inside the program loop.
• Add a 1 second delay so that we are not printing too fast

	int ledPin = 13;                // LED connected to digital pin 13
	int inputPin = 2;               // connect analog inputs to this pin
	int val;

	void setup()                    // run once, when the sketch starts
	{
	  pinMode(ledPin, OUTPUT);      // sets the digital pin as output
	  Serial.begin(9600);           // establish serial communication at 9600 baud
	}

	void loop()                     // run over and over again
	{
		
	  val = analogRead(inputPin);

	  digitalWrite(ledPin, HIGH);  
	  delay(val/50);
	  digitalWrite(ledPin, LOW);
	  delay((1023-val)/50);
	  
	  Serial.println(val);          // print val to serial
	  delay(1000);  
	}
	

Sensors

There are many sensor that behave just like variable resistors. For example, photo-resistor (aka cadmium sulfide or CdS cell) is a sensor that changes resistance based on the amount of light that hits it.
Using a photo-resistor to create analog voltage input (by making a voltage divider):

Thermistor is a sensor that varies resistance with a change in temperature. We need a relatively large temperature change to see the difference.

Flex Sensor changes its resistance by bending. This is the sensor that was apparently used in the original Nintendo Power Glove.

Some complicated sensors are designed to produce analog voltage as an output, making them easy to interface to Arduino. For example, some infra-red (IR) sensors produce a voltage level proportional to distance to an object in front of the sensor.

Transistors

So far we've discussed electronic components that can be directly manipulated by microcontroller's pins. Each digital output pin on the Arduino can provide about 25mA of current. This is enough to light an LED, but to control something that requires more current (e.g. motor), we can use a Transistor.

Transistors are devices that amplify electronic signals. There are two standard types, NPN and PNP. Transistors have three leads, base (B), collector (C) and emitter (E). The rule is that small base current in a transistor controls a larger collector current.

Relays

To control AC circuits using the Arduino, we use a transistor and a part called Relay, which is an electrical switch operated by an electromagnet.

Putting it all together

Let's design a circuit that uses a sensor as an input and a standard electric bulb as an output.