Programming Part 2

After understanding the basic structure of our program and how to store values, we need to explore how to interact with the components in our circuits.

Input

An input operation is one where we read or receive data from a component in our circuit - a sensor. As discussed in the Circuits section, different sensors can have digital as well as analog signals.

Signal	Arduino instruction	Explanation
Analog	analogRead(pin)	Returns an integer value between 0 and 1023 read on pin
Digital	digitalRead(pin)	Returns either 0 (LOW) or 1 (HIGH) read on pin

Example

// Read the value from a button connected to digital pin 2
buttonState = digitalRead(2);

// Read the value from a sensor connected to analog pin A3
sensorReading = analogRead(A3);

Output

Conversely, an output operation is one where we send data to a component in our circuit - an actuator.

Signal	Arduino instruction	Explanation
Analog	analogWrite(pin, value)	Sends a value between 0 and 1023 to pin
Digital	digitalWrite(pin, value)	Sends either 0 (LOW) or 1 (HIGH) to pin

Example

// Sending a HIGH signal (same as value 1) to pin 3
digitalWrite(3, HIGH);

// Sending a state of 123 to pin A1 
analogWrite(A1, 123);

Decision-making

To implement decision-making in programming, we use conditionals. They allow us to determine what should happen (which instructions should be executed) based on conditions we define.

Syntax

// A simple if conditional
if (condition) {
    // Instructions to be executed only if condition is true
} 

// if-else conditional
// used when we check for two possible outcomes of a condition
if (condition) {
    // Instructions to be executed if condition is true
} else {
   // Instructions to be executed if condition is false 
}

// if-else-if conditional
// used when we check for more than two possible outcomes of a condition
if (condition1) {
    // Instructions to be executed if condition1 is true
} else if (condition2) {
   // Instructions to be executed if condition1 is false but condition2 is true 
} else {
    // Instructions to be executed if all conditions are false 
}

Where condition can generally be one of the following:

Operator	Description	Example
==	Equality	buttonState == LOW
!=	Inequality	buttonState != LOW
>	Greater than	sensorReading > 300
>=	Greater than or equal	sensorReading >= 300
<	Less than	sensorReading < 300
<	Less than or equal	sensorReading <= 300

Serial

A very important programming functionality we'll use has to do with getting information from the Arduino as our program is being executed. The Serial port provides this communication and we don't need to create a circuit for it.

Configuration

void setup() {
    // Initiate the serial port and configure it to the transfer speed of 9600 bits per second
    Serial.begin(9600);
}

Manipulation

void loop(){
    // Print the reading from A0 always at a new line
    Serial.println( analogRead(A0) );

    // Wait 0.5seconds (500 milliseconds) before executing the loop function again
    delay(500);
}

Delay

As we saw in the last example, the delay() function can be used to pause the execution of our program for a specified time.

Syntax delay(number_of_milliseconds)

Example: delay(1000) for a 1sec pause, delay(5000) for 5secs, delay(50) for 50 milliseconds

This can be useful whenever when we need a pause between the execution of instructions and it is commonly placed as the last instruction in the loop function to provide a pause before executing it again.