UltraSense

A simple and intuitive Arduino library for the HC-SR04 ultrasonic sensor.
Supports distance readings in CM / MM / inches, object speed measurement, and a built-in motion detection mode — turning your HC-SR04 into a PIR-like presence sensor.

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Installation

1. From Arduino Library Manager (stable versions)

1. In the sidebar click library manager
2. Search for "UltraSense" (by OneDevelopment)
3. Click "Install"

2. Manual download (latest version)

1. Download the repository as a ZIP file
2. In Arduino IDE: Sketch → Include Library → Add .ZIP Library...
3. Select the downloaded file

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Wiring

HC-SR04     Arduino
-------     -------
VCC    →    5V
GND    →    GND
TRIG   →    pin 9  (or any digital pin)
ECHO   →    pin 10 (or any digital pin)

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Quick Start

#include <UltraSense.h>

UltraSense sensor(9, 10); // TRIG, ECHO

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

void loop() {
  float cm = sensor.readCM();

  if (sensor.isOutOfRange()) {
    Serial.println("Out of range");
  } else {
    Serial.println(cm);
  }

  delay(500);
}

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API

Initialization

Method	Description
UltraSense(trigPin, echoPin)	Constructor – provide TRIG and ECHO pin numbers
begin()	Initialize in standard mode
beginMotionDetection(sensitivity, windowMs)	Initialize in motion detection mode

beginMotionDetection parameters:

Parameter	Type	Default	Description
sensitivity	float	5.0	Minimum distance change [cm] to trigger motion
windowMs	uint16_t	500	Time [ms] of stillness before baseline refreshes

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Distance Readings

Method	Returns	Description
readCM()	float	Distance in centimeters
readMM()	float	Distance in millimeters
readInches()	float	Distance in inches
readAverageCM(samples)	float	Average of samples readings in CM (default 5)
readAverageMM(samples)	float	Average of samples readings in MM (default 5)
readAverageInches(samples)	float	Average of samples readings in inches (default 5)
readRaw()	long	Raw echo duration in microseconds

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Range & Speed

Method	Returns	Description
isOutOfRange()	bool	true when object is out of range (~400 cm) or no echo received
getSpeed(delayMs)	float	Object speed in cm/s; negative = approaching, positive = moving away; delay between measurements defaults to 50 ms

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Motion Detection

Available only after calling beginMotionDetection().

Method	Description
update()	Required in loop() – checks for motion, fires callback, refreshes baseline
motionDetected()	Returns true if motion was detected since last call (auto-reset)
onMotion(callback)	Registers a function called automatically when motion is detected
setSensitivity(cm)	Change sensitivity at runtime
setWindowMs(ms)	Change stillness window at runtime

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How Motion Detection Works

The HC-SR04 has no built-in motion sensing, but UltraSense simulates it:

1. Calibration – beginMotionDetection() takes several readings and establishes a baseline (the reference distance of the environment)
2. Detection – on every update() call, the current reading is compared to the baseline; if the difference ≥ sensitivity → motion detected
3. Adaptation – when no motion is detected for windowMs ms, the baseline is gently updated using EMA (α = 0.2), so the sensor adapts to slow environmental changes (e.g. temperature drift)
4. Freeze – while motion is ongoing, the baseline is not updated

Distance
  │        baseline ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─
  │                          ↑ motion!
  │                    ┌─────┘     └─────┐
  │────────────────────┘                 └──────
  └──────────────────────────────────────────→ time

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Examples

Sketch	Description
01_BasicDistance	Read CM / MM / inches with out-of-range handling
02_AverageAndSpeed	Averaged readings and object speed measurement
03_MotionDetection_Polling	PIR-like motion detection – poll motionDetected() in loop()
04_MotionDetection_Callback	PIR-like motion detection – automatic callback + buzzer

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Practical Tips

Sensitivity vs environment:

• In a quiet indoor space you can set sensitivity to 3–4 cm
• In a place with vibrations or air movement, increase it to 8–10 cm

Measurement speed:

• getSpeed(delayMs) blocks execution for delayMs ms – avoid very short values if responsiveness matters
• In motion detection mode, update() takes ~30–50 ms per call (one HC-SR04 measurement)

HC-SR04 limitations:

• Range: ~2 cm – ~400 cm
• Beam angle: ~15°
• Minimum interval between measurements: ~60 ms (the library handles this internally)
• Speed of sound assumed at 343 m/s (~20°C)

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License

MIT License – free to use, modify and distribute.

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Author

OneDevelopmentPL