Switch (case) Statement, used with sensor input

An if statement allows you to choose between two discrete options, TRUE or FALSE. When there are more than two options, you can use multiple if statements, or you can use the switch statement. Switch allows you to choose between several discrete options. This tutorial shows you how to use it to switch between four desired states of a photo resistor: really dark, dim, medium, and bright.

This program first reads the photoresistor. Then it uses the map() function to map its output to one of four values: 0, 1, 2, or 3. Finally, it uses the switch() statement to print one of four messages back to the computer depending on which of the four values is returned.

Hardware Required

  • Arduino or Genuino Board
  • photoresistor, or another analog sensor
  • 10k ohm resistors
  • hook-up wires
  • breadboard

Circuit

The photoresistor is connected to analog in pin 0 using a voltage divider circuit. A 10K ohm resistor makes up the other side of the voltage divider, running from Analog in 0 to ground. The analogRead() function returns a range of about 0 to 600 from this circuit in a reasonably lit indoor space.

click the image to enlarge

image developed using Fritzing. For more circuit examples, see the Fritzing project page

Schematic

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Code

/*
  Switch statement

  Demonstrates the use of a switch statement. The switch statement allows you
  to choose from among a set of discrete values of a variable. It's like a
  series of if statements.

  To see this sketch in action, put the board and sensor in a well-lit room,
  open the Serial Monitor, and move your hand gradually down over the sensor.

  The circuit:
  - photoresistor from analog in 0 to +5V
  - 10K resistor from analog in 0 to ground

  created 1 Jul 2009
  modified 9 Apr 2012
  by Tom Igoe

  This example code is in the public domain.

  http://www.arduino.cc/en/Tutorial/SwitchCase
*/


// these constants won't change. They are the lowest and highest readings you
// get from your sensor:
const int sensorMin = 0;      // sensor minimum, discovered through experiment
const int sensorMax = 600;    // sensor maximum, discovered through experiment

void setup() {
  // initialize serial communication:
  Serial.begin(9600);
}

void loop() {
  // read the sensor:
  int sensorReading = analogRead(A0);
  // map the sensor range to a range of four options:
  int range = map(sensorReading, sensorMin, sensorMax, 0, 3);

  // do something different depending on the range value:
  switch (range) {
    case 0:    // your hand is on the sensor
      Serial.println("dark");
      break;
    case 1:    // your hand is close to the sensor
      Serial.println("dim");
      break;
    case 2:    // your hand is a few inches from the sensor
      Serial.println("medium");
      break;
    case 3:    // your hand is nowhere near the sensor
      Serial.println("bright");
      break;
  }
  delay(1);        // delay in between reads for stability
}

See Also


Last revision 2015/08/11 by SM

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