Ard Constrain Range

In this tutorial, you'll learn about Arduino constrain() Not Clamping Values. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

The Problem

constrain() does not prevent values from exceeding the expected range.

Quick Fix

Wrong

int val = constrain(raw, 0, 255);  // Works, but only constrains, does not map

Values are clamped but may not be in the desired range if raw is out of bounds.

Right

int raw = analogRead(A0);
// Constrain to 0-255 range after mapping
int val = map(raw, 0, 1023, 0, 255);
val = constrain(val, 0, 255);  // Extra safety
analogWrite(9, val);
Serial.print("PWM: ");
Serial.println(val);

PWM: 127  (safe value between 0 and 255).

Prevention

constrain() clamps a value between a minimum and maximum. It does not rescale or map — use map() for scaling. Typical usage: constrain(map(input, 0, 1023, 0, 255), 0, 255). constrain works with any numeric type (int, float, long).

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FAQ