Arduino Programming – Map and smooth values

Re-map a value from one range to another and smooth analog input values.

Level : beginner with Arduino. ( Basic knowledge of programming principles like if/else and variables ).

Download the Arduino ( .pde ) files : arduino_tutorial_map-and-smooth.zip

Map.pde :

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/* 

  Mapping example



  Re-map a number from one range to another. 



  created 01-12-2009 by kasperkamperman.com

*/



const int sensorPin = 0;    // the pin that the potmeter is attached to

int sensorValue     = 0;    // store the value coming from the sensor

int mappedValue;            // store the new value



void setup() {

  // opens serial port, sets data rate to 57600 bits per second

  Serial.begin(57600);

}



void loop() {

  // read the value from the sensor

  // the range from an analog input is 0 - 1023

  sensorValue = analogRead(sensorPin);  



  // print the value

  Serial.print("sensorValue                                 : ");

  Serial.println(sensorValue);   



  // map(value, fromLow, fromHigh, toLow, toHigh)

  mappedValue = map(sensorValue, 0, 1023, 0, 255);



  Serial.print("map to 0 - 255                              : ");

  Serial.println(mappedValue);  



  // invert a value is possible too 

  mappedValue = map(sensorValue, 0, 1023, 255, 0);



  Serial.print("map to 255 - 0                              : ");

  Serial.println(mappedValue);  



  // or negative values

  mappedValue = map(sensorValue, 0, 1023, -127, 128);



  Serial.print("map to -127 - 128                           : ");

  Serial.println(mappedValue);  



  // only watch a certain part of the sensor values

  // for example when using a sensor that doesn't cover the whole

  // range

  mappedValue = map(sensorValue, 512, 712, 0, 100);

  Serial.print("map 512 - 712 to 0 - 100                    : ");

  Serial.println(mappedValue);



  // constraining the sensorValue can be usefull to prevent negative values

  sensorValue = constrain(sensorValue, 512, 712);  

  Serial.print("constrained sensorValue                     : ");

  Serial.println(sensorValue);



  mappedValue = map(sensorValue, 512, 712, 0, 100);

  Serial.print("map 512 - 712 to 0 - 100 ( with constrain ) : ");

  Serial.println(mappedValue); 



  // division between next read

  Serial.println("------------------------------------------------");



  // wait for 1000 milliseconds ( 1 second ) to read every second

  delay(1000);

}

Analog_smooth.pde :

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/* 

  Smoothing example



  Read the analog input and smooth out the result by averaging

  the result with past values of the input.



  The more samples to longer it takes to reach the final value. 

  4/5 samples give a smooth and reactive enough result. 



  Simpler algorithm than the smoothing included with the Arduino 

  examples.



  based on : Analog Smoothing Algorithm by Tom Igoe 

  <http://www.tigoe.net/pcomp/code/category/arduinowiring/41>



  created 05-01-2010 by kasperkamperman.com

*/



const int sensorPin = 0;    // the pin that the potmeter is attached to



int sensorVal       = 0;    // store the value coming from the sensor

int smoothedVal     = 0;    // smoothed result

int samples         = 4;    // amount of samples



void setup() {

  Serial.begin(57600);

}



void loop() {



  // read the value from the sensor

  // the range from an analog input is 0 - 1023

  sensorVal = analogRead(sensorPin); 



  smoothedVal = smoothedVal + ((sensorVal - smoothedVal)/samples);



  // print the original value and the smoothedValue

  Serial.print(sensorVal); 

  Serial.print(", ");

  Serial.println(smoothedVal); 



  // slow down amount of readings and prints

  delay(100); 



}