🔌 Lost + Found HC-SR04 Ultrasonic Distance Sensor Driver

This driver provides a simple, hardware-independent interface for the HC-SR04 ultrasonic distance sensor module on the Raspberry Pi Pico 2 (RP2350).

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🎛️ Hardware Description & Specifications

The HC-SR04 uses ultrasonic waves (sound at 40 kHz) to determine the distance to an object. It works by sending an acoustic pulse (trigger) and measuring the time it takes for the echo to bounce back to the receiver.

📐 Sensor Characteristics & Tentative Specifications

• Operating Voltage: 5V (from VBUS on the Pico)
• Measurement Angle: < 15 degrees
• Detection Distance/Range: 2 cm to 400 cm
• Accuracy: Up to 3 mm deviation under ideal conditions
• 5V Tolerance: Because the Raspberry Pi Pico 2 GPIO pins are 5V tolerant when powered, the sensor's Echo pin output can be connected directly to the digital inputs (like GP15) without level shifters.

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🔌 Wiring Diagram (Pico 2)

Sensor Pin	Pico 2 GPIO Pin	Pico 2 Physical Pin	Notes
VCC	VBUS	Pin 40	Power input (5V from USB).
Trig	GP14	Pin 19	Trigger output from Pico (3.3V logic level).
Echo	GP15	Pin 20	Echo input to Pico (5V logic, safe on Pico 2 digital GPIO).
GND	GND	Pin 38 (or any GND)	Common ground reference.

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🚀 Usage Example

#include "pico/stdlib.h"
#include "lf_hcsr04.h"
#include <stdio.h>

#define TRIG_PIN 14
#define ECHO_PIN 15

int main() {
    stdio_init_all();
    
    lf_hcsr04_t sensor;
    if (!lf_hcsr04_init(&sensor, TRIG_PIN, ECHO_PIN)) {
        printf("Failed to initialize HC-SR04 driver\n");
        return -1;
    }
    
    while (true) {
        float distance_cm = lf_hcsr04_read_distance_cm(&sensor);
        if (distance_cm >= 0.0f) {
            printf("Distance: %.2f cm\n", distance_cm);
        } else {
            printf("Measurement error: %.1f\n", distance_cm);
        }
        sleep_ms(500);
    }
}