Using map()
When working with sensor readings one of the most useful functions the Wiring language offers is map():
map( value, from_min, from_max, to_min, to_max)
Map takes 5 parameters or passed variables as follows:
-
value - the name of the variable with the value that you want to transform
-
from_min - the lower bound of the range that the value is currently in
-
from_max - the upper bound of the range that the value is currently in
-
to_min - the lower bound of the range that you want to transform the value to
-
to_max - the upper bound of the range that you want to transform the value to
It’s really flexible and great for transforming sensor readings into PWM ranges, or inverting ranges.
An example - convert to PWM range
int lightSensorPin = A0; // connected to analog pin 0
void loop()
{
int val = analogRead(lightSensorPin); // read from the sensor
// analogRead gives us the range 0-4095
// when we fade an LED we want it in the range 0-255
// map lets it convert the value like this...
int ledValue = map( val, 0, 4095, 0, 255);
}
Another example - invert a range
int invertedValue = map( val, 0, 4095, 4095, 0);
Another example - shift a range
Note that it can also handle negative numbers!
int invertedValue = map( val, 0, 100, -50, 50);