map and constrain in Arduino

Rescale one range onto another, then clip the edges.

// map rescales one range onto another; constrain clips the edges.
const int KNOB_PIN = A1;
const int VENT_PIN = 6;

void setup() {
  pinMode(VENT_PIN, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int knob = analogRead(KNOB_PIN);
  // 0-1023 counts onto 0-255 PWM, then clipped to a safe band.
  int duty = map(knob, 0, 1023, 0, 255);
  duty = constrain(duty, 20, 235);
  analogWrite(VENT_PIN, duty);
  Serial.println(duty);
  delay(100);
}

How it works

1. map(knob, 0, 1023, 0, 255) moves counts onto PWM duty.
2. constrain(duty, 20, 235) keeps the vent in its safe band.
3. Knob to vent in two library calls, no arithmetic by hand.

Keywords and builtins used here

• OUTPUT
• Serial
• analogRead
• analogWrite
• begin
• const
• constrain
• delay
• int
• loop
• map
• pinMode
• println
• setup
• void

The run, in numbers

Lines

18

Characters to type

427

Tokens

94

Three-star pace

65 tpm

At the three-star pace of 65 tokens a minute, this run takes about 87 seconds.

Type this snippet

Step 2 of 3 in Analog, step 8 of 27 in Language basics.

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