hc-sr04 v0.1.0

HC-SR04 ultrasonic distance sensor.

Application scenarios

• A parking or obstacle sensor.
• Tank or bin level measurement.
• A simple presence detector.

Contract

uint8_t hc_sr04_read(hc_sr04_port_t port, uint32_t *millimeters);
uint32_t hc_sr04_millimeters(uint32_t echo_us);

• read triggers one measurement and measures the echo pulse.
• millimeters is the round-trip distance at 343 m/s.
• Returns 1 on success, 0 for an out-of-range echo.
• hc_sr04_millimeters is the pure conversion, useful for capture ISRs.

Parameters

• Measure echoes from about 100 us to 60 ms.
• Keep the sensor perpendicular to a flat target.
• The speed of sound changes with temperature; this unit uses 343 m/s.

Memory and timing

• 4 bytes; one trigger and one pulse measurement.
• A 60 ms maximum echo limits the range to about 10 m.

Integration

uint32_t millimeters;
if (hc_sr04_read(board_hc_sr04_port(), &millimeters)) {
    show(millimeters);
}

Adapters

• The adapter drives TRIG high for 10 us, then measures ECHO high time.
• Reference: LibDriver hcsr04 (MIT) and the HC-SR04 datasheet.
• This implementation is original.

When not to use

• A soft or angled target; use a different ranging principle.
• Multiple sensors without cross-talk sequencing.

Verification

make test covers a nominal echo, the minimum and maximum range, and a

short/invalid echo.

void *context;
void (*trigger)(void *context);
uint32_t (*echo_pulse_us)(void *context);