HC-SR04 Ultrasonic Sensor Specifications and Features - Complete Guide

Overview of the HC-SR04

The HC-SR04 is a low-cost ultrasonic distance sensor commonly used in hobby, education and prototyping projects. It uses ultrasonic pulses (40 kHz) to measure distance by timing the echo return. This guide breaks down key specifications, electrical requirements, timing formulas, wiring examples, and practical South African considerations for sourcing and using the HC-SR04 in maker and educational projects.

Key specifications

How the HC-SR04 measures distance

Operation sequence: the microcontroller sends a 10 us high pulse to TRIG. The module emits an ultrasonic burst (~8 cycles at 40 kHz) and sets ECHO high. ECHO stays high until the echo is received; pulse width (t_echo) is proportional to the round-trip time of sound.

Convert t_echo to distance using the speed of sound (approximately 343 m/s at 20 degreesC). Basic formula:

distance (m) = (t_echo (s) * speed_of_sound (m/s)) / 2

Commonly used simplified formula in centimetres:

distance (cm) = t_echo (us) / 58

(Note: using speed_of_sound = 343 m/s gives t_echo/58; changes in ambient temperature affect the constant.)

Temperature correction

Speed of sound varies with air temperature: c ~ 331.4 + 0.6 * T (m/s), where T is degreesC. For accurate work in South African conditions (e.g., 5 degreesC to 35 degreesC), adjust calculations accordingly. For wiring examples and an Arduino integration walkthrough, see tutorial on integrating HC-SR04 with Arduino.

If you need sourcing options within South Africa, check buy BMT ultrasonic sensor HC-SR04 online in South Africa for local purchase guidance.

For common problems like false echoes, noisy readings, or wiring mistakes, refer to troubleshooting common issues with HC-SR04 sensors.

Wiring and example code snippets

Typical HC-SR04 pinout: VCC, TRIG, ECHO, GND. VCC is 5 V. Microcontroller GPIOs must tolerate 5 V on the echo pin; if using 3.3 V devices (many Raspberry Pi or some MCUs), use a level shifter or simple resistor divider on ECHO.

Simple wiring ASCII diagram

  +5V ----- VCC (HC-SR04)
  GND  ----- GND (HC-SR04)
  GPIOx ----- TRIG (HC-SR04)
  GPIOy <---- ECHO (HC-SR04)  [use level shifting for 3.3V GPIOs]

Arduino timing example (concept)

1. Set TRIG LOW for 2 us. 2. TRIG HIGH for 10 us. 3. Read pulse width on ECHO (pulseIn). 4. distance_cm = pulseWidth / 58.0.

Practical selection and troubleshooting

• Surface and angle: small or soft targets (cloth, foam) reflect poorly; aim perpendicular to the surface for best results.
• Minimum range: objects closer than ~2 cm may not be detected reliably.
• Interference: avoid using multiple HC-SR04 modules simultaneously without synchronization, as echoes can cross-talk.
• Power supply: use a stable 5 V source; noisy supply can cause false readings.
• Pulse timing: ensure microcontroller timers and blocking delays are appropriate for your sampling rate.

Example calculations with South African context

Example: at 25 degreesC, speed of sound ~ 331.4 + 0.6*25 = 346.4 m/s. If measured t_echo = 11600 us (0.0116 s):

distance = 0.0116 * 346.4 / 2 ~ 2.010 m (201 cm)

If using the simple divider: 11600 us / 58 ~ 200 cm (close to corrected value).

Local buying and classroom use notes (South Africa)

Communica stocks a range of ultrasonic modules, sensors and related prototyping accessories in categories such as Sensors & Semiconductors and Robotics & Prototyping. For students and educators: order quantities for labs may incur lead times; check branch stock at Samrand, Pretoria CBD or Cape Town for collection. Prices and availability in ZAR vary; typical hobby HC-SR04 modules are low-cost but buying genuine modules or branded sensor breakout boards can improve reliability.

Troubleshooting checklist

• No echo: confirm VCC/GND and TRIG pulse is reaching module; check with scope or logic probe.
• Spurious readings: add median filtering or take several samples and average; check for nearby reflective surfaces.
• Incorrect range on Pi: ensure ECHO is reduced to 3.3 V using voltage divider or level shifter.
• Cross-talk in multi-sensor arrays: stagger measurement times or use shielding/enclosures.

Sources

• HC-SR04 module datasheet (SparkFun mirror)
• Arduino PING Ultrasonic Tutorial
• Raspberry Pi community documentation and forum
• Communica Sensors collection