Build an Ultrasonic Parking Sensor

Understand the target result

Combine distance measurements with LED and buzzer warning patterns. The expected result is: Alerts become faster or change color as an object approaches.

Prepare the board and parts

Disconnect the ESP32 from USB. Put the ESP32, breadboard, jumper wires, and the listed lesson parts in front of you. Straighten bent pins gently and never force a module into the breadboard.

Make each connection with power off

1. Wire HC-SR04 as in Lesson 23: TRIG GPIO 5 and divided ECHO GPIO 18.
2. Green LED → resistor → GPIO 23; yellow LED → resistor → GPIO 22; red LED → resistor → GPIO 21.
3. Active buzzer positive → GPIO 19 and negative → GND.
4. Connect every ground together.

Install any library and upload the code

No additional Arduino library is required for this starter sketch. Select your ESP32 board and serial port before clicking Upload.

const int TRIG=5,ECHO=18,GREEN=23,YELLOW=22,RED=21,BUZZER=19;
float distanceCm(){ digitalWrite(TRIG,LOW);delayMicroseconds(2);digitalWrite(TRIG,HIGH);delayMicroseconds(10);digitalWrite(TRIG,LOW);return pulseIn(ECHO,HIGH,30000)*0.0343/2.0; }
void setup(){ pinMode(TRIG,OUTPUT);pinMode(ECHO,INPUT);pinMode(GREEN,OUTPUT);pinMode(YELLOW,OUTPUT);pinMode(RED,OUTPUT);pinMode(BUZZER,OUTPUT); }
void loop(){
  float cm=distanceCm(); bool near=cm>0&&cm<15, medium=cm>=15&&cm<35;
  digitalWrite(RED,near);digitalWrite(YELLOW,medium);digitalWrite(GREEN,!near&&!medium);
  digitalWrite(BUZZER,near); delay(near?100:250); digitalWrite(BUZZER,LOW); delay(near?100:250);
}

Power the circuit and observe

Connect USB power only after the wiring check. Open Serial Monitor at 115200 baud when the sketch prints data. Watch the circuit for at least 20 seconds and compare it with this expected behavior: Alerts become faster or change color as an object approaches.

Change one value and test again

Make one small change—such as a delay, threshold, brightness, or displayed message—then upload again. This confirms that you understand which part of the program controls the result.