การต่อสาย Trigger และ Echo

The HC-SR04 has four pins in a row: VCC, Trig, Echo, and GND. Get these connected correctly and the sensor just works.

Connect VCC to the Arduino 5V pin. This sensor needs a full 5 volts to charge up and fire its sound pulses properly.

Wire GND to an Arduino GND pin. Without a shared ground, the signals have no common reference and your readings turn to nonsense.

The Trig pin is the sensor's input. When you pulse it HIGH for a moment, the sensor sends out its burst of ultrasonic sound.

The Echo pin is the sensor's output. It goes HIGH for exactly as long as the sound is travelling out and bouncing back.

Connect Trig and Echo to any two digital pins, for example pin 9 and pin 10. You will name these in code so the Arduino knows where to look.

At the top of your sketch, give each pin a clear name. Constants make the rest of your code far easier to read and edit later.

In setup, declare Trig as OUTPUT so you can drive it, and Echo as INPUT so the Arduino can read the returning pulse.

The Echo pin outputs 5V, which a standard Uno reads fine. On a 3.3V board like an ESP32, add a divider so you do not over-volt the pin. ⚠️

Plug the sensor and jumper wires into a breadboard for solid, tidy connections. Loose wires are the top cause of flickering readings.

Never swap VCC and GND. Before powering on, trace each wire once more so you protect both the sensor and your board.

Think about which pin does what.

Power, ground, and two named digital pins, that is the whole hookup. With Trig driving and Echo listening, you are ready to time the pulse. ✅