The **SR-04** (commonly referred to as the HC-SR04) is an ultrasonic distance sensor used widely in robotics and electronics projects. It operates on the principle of **sonar**, using sound waves to determine the distance to an object. --- ### 1. Key Electronic Specifications The performance of the sensor depends on these electrical parameters: | Parameter | Specification | | :--- | :--- | | **Operating Voltage** | 5V DC | | **Operating Current** | 15mA | | **Working Frequency** | 40 kHz | | **Max Range** | 4 meters | | **Min Range** | 2 cm | | **Measuring Angle** | 15 degrees | | **Trigger Input Signal** | 10µs TTL pulse | --- ### 2. Pin Configuration The sensor features a 4-pin interface for communication with microcontrollers (like Arduino or ESP32): 1. **VCC**: Power supply (5V). 2. **Trig (Trigger)**: Input pin. Sending a high pulse here initiates the measurement. 3. **Echo**: Output pin. This pin stays HIGH for the duration it takes for the sound wave to return. 4. **GND**: Ground. --- ### 3. Core Components The board consists of several specialized electronic parts: * **Ultrasonic Transmitter (T)**: A transducer that converts electrical energy into 40kHz sound pulses. * **Ultrasonic Receiver (R)**: A transducer that detects the reflected sound waves and converts them back into electrical signals. * **Control Circuitry**: Usually involves an integrated circuit (IC) like the **LM324** (Quad Operational Amplifier) to amplify the weak signal received by the receiver, and a microprocessor/timer to handle the logic. --- ### 4. Working Logic (Code Implementation) To use the sensor, you must trigger it and then measure the timing of the pulse on the Echo pin. ```cpp // Example Arduino Code Snippet long duration; int distance; digitalWrite(trigPin, LOW); delayMicroseconds(2); digitalWrite(trigPin, HIGH); // Send 10us pulse delayMicroseconds(10); digitalWrite(trigPin, LOW); duration = pulseIn(echoPin, HIGH); // Read time in microseconds distance = duration * 0.034 / 2; // Calculate distance (Speed of sound = 340m/s) ``` --- ### 5. Distance Calculation Formula The distance is calculated based on the speed of sound ($v \approx 340\text{ m/s}$ or $0.034\text{ cm/µs}$): $$\text{Distance} = \frac{\text{Time} \times \text{Speed of Sound}}{2}$$ *Note: We divide by 2 because the sound travels to the object and back.*