A robot is constituted of four main components: Motors for motion, Mechanics to hold the pieces together, sensors to make it react to environment and a code to control them and create the desired functionality.

Sensors plays an important role when dealing with autonomous robot. We’ll see here how to use them.

Presentation

The purpose of a sensor is to measure a physical value (velocity, angle, temperature, etc.). There are numerous sensors of different types passive and active (require powering). In this example, we use a photoresistor but it can be applied to other type of sensor.

Here is a list of sensor :

Passif:

• photoresistor
• tilt
• push button

Actif:

• infrared distance sensor
• ultrasonic distance sensor

Wiring

Sensor have different wiring depending on the number of pin they use. They ususally have 3 pins ground, voltage supply 5V and the signal. For passive sensor, a third output as to be created to read the voltage at its ends.

Base code to read sensor

Depending on its type, sensor can return two informations: a state (presence or not) or a continous voltage value.

To read a state, the function to use is digitalRead(). It returns a level HIGH or LOW which represent the voltage applied on the digital pin (0, 1 , 2, etc.).

/*Read digital state*/
// Constants
#define DELAY 500 // Delay between two measurements in ms

// Parameters
const int sensorPin = 2; // Pin connected to sensor

//Variables
int sensorState; // state from the sensor

void setup(void) {
  Serial.begin(9600);
  pinMode(sensorPin,INPUT);
}

void loop(void) {
  sensorState = digitalRead(sensorPin);
 
  if (sensorState == HIGH) {
     Serial.print("Sensor state is HIGH ");
  } else {
     Serial.print("Sensor state is LOW ");
  }
  delay(DELAY);
}

To read a continuous value, the function we use is analogRead() . It returns a value between 0 and 1023 representing the voltage applied on the Arduino analog pin (A0, A1, A2, etc.).

/*Read analog signal*/
// Constants
#define DELAY 500 // Delay between two measurements in ms

// Parameters
const int sensorPin = A0; // Pin connected to sensor

//Variables
int sensorVal; // Analog value from the sensor

void setup(void) {
  Serial.begin(9600);
}

void loop(void) {
  sensorVal = analogRead(sensorPin);
  Serial.print("Sensor reading = ");
  Serial.println(sensorVal); // the analog reading
  delay(DELAY);
}

Use cases

• Measure temperature and humidity with sensor DHT11
• Measure temperature with sensor LM35
• Distance measurement with sensor HC-SR04
•  Luminosity measurement with a photoresistor