The idea is simple: the closer you are to an obstacle, the higher the pitch of the buzzer. Move away, pitch drops. Your ears do the work so your eyes don't have to.
The HC-SR04 ultrasonic sensor fires a pulse and measures how long the echo takes to return. That gives you distance in centimeters. Straightforward enough. The less straightforward part was making it actually feel right to use. Linear pitch mapping sounded wrong, equal distance steps felt unequal in pitch, which is just how human hearing works. Switching to a logarithmic scale fixed it. The buzzer finally felt like it was communicating something rather than just making noise.
Raw sensor readings are jittery. Without a rolling average filter the buzzer stuttered constantly and was basically unusable. Adding the filter smoothed everything out. That's the kind of thing you only figure out by wiring it up and listening to it.
The rest of the system: a 16x2 LCD shows the live distance reading, the ESP32 hosts a web dashboard you can pull up in any browser on the same network, and the Blynk app lets you mute or control the system remotely from your phone.
The hardest part wasn't the code. It was reading through datasheets and pin diagrams to figure out where everything actually connects. The HC-SR04 docs are not written for people who are new to this, and the ESP32 has a lot of pins. Got the wiring wrong twice before it worked.
Built this in July 2025 at the IIIT Delhi Electronics Design Carnival, ECE department, among B.Tech students and engineers. Two weeks of circuit design, PCB layout, IoT, 3D printing, and prototyping. Certificate signed by Prof. A V Subramanyam, HoD ECE. Industry partners on the program: Keysight, LPKF, Bergen Associates.