BeginnerSensors

Ultrasonic Parking Distance Beeper

Measure nearby objects with an HC-SR04 and make a buzzer beep faster as an object gets closer.

Estimated time: 60–90 minutes · Skills: Digital inputs and outputs, pulse timing, simple thresholds

Parts from the database

Other supplies

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Connections

  1. HC-SR04 VCC to 5 V and GND to GND; TRIG to D9 and ECHO to D10 on a 5 V Uno-compatible board.
  2. Piezo buzzer positive to D3 and negative to ground. Use a small piezo buzzer, not a loudspeaker.
  3. If using a 3.3 V board instead, level-shift the HC-SR04 ECHO output before connecting it to the MCU.

Build steps

  1. Upload the sketch and open Serial Monitor at 9600 baud.
  2. Place a flat target 20–150 cm from the sensor; keep the sensor face clear.
  3. Confirm the displayed distance changes consistently as you move the target.
  4. Listen for beeps that speed up below the selected threshold; tune the thresholds for your enclosure.

Software and firmware setup

const int trigPin=9, echoPin=10, buzzerPin=3;
void setup(){ Serial.begin(9600); pinMode(trigPin,OUTPUT); pinMode(echoPin,INPUT); pinMode(buzzerPin,OUTPUT); }
void loop(){
  digitalWrite(trigPin,LOW); delayMicroseconds(3);
  digitalWrite(trigPin,HIGH); delayMicroseconds(10); digitalWrite(trigPin,LOW);
  unsigned long us=pulseIn(echoPin,HIGH,30000);
  if(us==0){ noTone(buzzerPin); Serial.println("No echo"); delay(100); return; }
  float cm=us*0.0343f/2.0f; Serial.println(cm);
  if(cm<100){ int interval=map((int)cm,5,100,80,700); tone(buzzerPin,2200,40); delay(max(interval,80)); }
  else { noTone(buzzerPin); delay(100); }
}

Review the pin assignments in the sketch against the wiring table before uploading.

Test your build

A target moving from about 100 cm toward the sensor should produce progressively faster chirps. The result is a bench demonstrator, not an automotive parking safety system.

Troubleshooting

  • If readings are zero, check TRIG/ECHO order and the 5 V supply.
  • Soft fabric and angled surfaces reflect ultrasound poorly; test with a flat cardboard book.
  • If the buzzer is silent, check whether it is an active buzzer or a passive piezo; this sketch uses tone().

Safety and limitations

This is only a tabletop demo. Do not use it to guide a real vehicle or rely on it to prevent a collision.

Manufacturer and platform documentation

Community Notes for This Project

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