Ultrasonic Ranging Special: Electronic Ruler · Parking Radar · Liquid-Level Detection

📏 Ultrasonic Ranging — The Robot's Eye

🔊 HC-SR04 Workflow

1. Trig pin sends a ≥10µs high pulse
2. Sensor emits 8 pulses at 40kHz
3. Ultrasound reflects off the obstacle
4. Echo outputs a high pulse whose width = round-trip time
5. Distance = pulse width (µs) ÷ 58 (cm)

🧪 Three Projects

• Electronic ruler: 2~400cm range, ±3mm, LCD display, switchable units
• Parking radar: >50cm silent / 30-50cm slow beep / 10-30cm fast beep / <10cm continuous buzz + red
• Liquid-level detection: measure above the water surface; pump on below the warning line, off at the upper limit to prevent overflow