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HC-SR04 ultrasonic distance sensor
The HC-SR04 is a 5V ultrasonic distance sensor with a 2–400 cm range and ±3 mm accuracy, using 40 kHz sound waves and time-of-flight measurement to provide reliable, non-contact distance readings for embedded systems.
Overview
The HC-SR04 is a widely used ultrasonic sensor module that measures distance by emitting ultrasonic waves (sound) and calculating the time it takes for the echo to return using the Time of Flight principle.
⚙️ Electrical Specifications
Operating Voltage: 5V DC
Operating Current: ~15 mA (typical)
Quiescent Current: < 2 mA
Power Consumption: ~75 mW
📏 Measurement Specifications
Measuring Range: 2 cm – 400 cm (0.02 m – 4 m)
Optimal Range: 2 cm – 200 cm
Accuracy: ±3 mm
Resolution: ~3 mm
Measuring Angle: ~15°
⏱️ Timing Characteristics
Trigger Input Pulse: ≥ 10 µs HIGH signal
Echo Output Pulse: Width proportional to distance
Cycle Time: ≥ 60 ms between measurements
Response Time: < 200 ms
🔊 Ultrasonic Specifications
Operating Frequency: 40 kHz
Ultrasonic Output: 8-cycle burst at 40 kHz
Detection Method: Reflection of ultrasonic waves
🔌 Pin Configuration
The HC-SR04 has 4 pins:
VCC – +5V power supply
Trig (Trigger) – Input pin to start measurement
Echo – Output pin (returns pulse width)
GND – Ground
🧠 Working Principle
Send a 10 µs HIGH pulse to the Trig pin
Sensor emits ultrasonic waves
Waves hit an object and reflect back
Echo pin outputs a pulse duration proportional to distance
Distance is calculated using the Speed of Sound:
d=
2
v×t
Where:
d = distance
v = speed of sound (~343 m/s)
t = time of echo pulse
🌡️ Environmental Conditions
Operating Temperature: 0°C to 40°C
Storage Temperature: −20°C to 70°C
Humidity: < 95% RH (non-condensing)
📐 Physical Specifications
Dimensions: ~45 mm × 20 mm × 15 mm
Weight: ~9 g
Mounting: 2 holes on PCB
Transducers: Two cylindrical ultrasonic emitters/receivers
🔗 Compatibility
Works with:
Arduino (Uno, Mega, Nano)
ESP32 / ESP8266
Raspberry Pi (with level shifting recommended)
Other microcontrollers
⚡ Key Features
Low cost and easy to use
Non-contact distance measurement
Stable and reliable for short-range sensing
Good accuracy for hobby and robotics projects
⚠️ Limitations
Affected by:
Soft surfaces (absorb sound)
Angled surfaces (deflect sound)
Temperature variations (affect sound speed)
Cannot measure very small (<2 cm) or very far (>4 m) objects accurately
Not suitable for outdoor use in heavy wind or rain
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