Keep Values in Range

Part of the Inputs section of Coddy's Arduino journey. Lesson 11 of 22.

Sometimes only part of a range should count. Say only the middle of the knob's travel matters, readings 200 to 800, and that should be 0 to 100 percent:

int percent = map(reading, 200, 800, 0, 100);

That gives 0 at 200 and 100 at 800, but map() does not stop at the ends of the range. A reading of 0 gives -33, and 1023 gives 137. A percent below 0 or above 100 makes no sense.

constrain(x, low, high) keeps a number inside a range: anything below low becomes low, anything above high becomes high, and everything in between stays as it is.

percent = constrain(percent, 0, 100);

Challenge

Easy

The knob is on A0. Print a percent where readings 200 to 800 count as 0 to 100:

map the reading from 200 to 800 into 0 to 100
keep it between 0 and 100 with constrain()
print it, then wait 100 ms

Press Run, turn the knob all the way both ways, then Check.

Try it yourself

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

void loop() {
  int reading = analogRead(A0);
  // map 200..800 to 0..100, keep it in 0..100, print it, wait 100 ms
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Inputs

Practice on your own: Arduino playground