Digital Display Control Board for HC-SR04 Ultrasonic Sensor, STM8S103

This control board gives a standalone, visual readout for an HC-SR04 ultrasonic distance sensor, built around an onboard STM8S103 8-bit microcontroller that handles the sensor timing, distance calculation, and display driving all on one small board, without needing a separate Arduino or other microcontroller to interpret the HC-SR04's raw timing signal. A digital tube display shows the current distance reading directly in centimeters, making it useful as a standalone measurement tool or a quick way to verify an HC-SR04 sensor is working correctly before integrating it into a larger project.

Beyond the onboard display, the board also outputs the same distance data over a serial connection at 9600 baud, in a simple format ("D:" followed by the distance value in centimeters and a line ending), letting a separate microcontroller or computer log or display the same readings through a UART connection rather than reading the HC-SR04's raw echo timing directly. This dual output (visual display plus serial data) makes the board useful both as a bench testing tool for verifying sensor performance and as a simplified interface that offloads the timing-measurement work from a project's main microcontroller.

Valid measurement range is rated at 3cm to 400cm, and the board includes TX and RX serial pins alongside NRST and SWIM pins specifically for reprogramming the onboard STM8S103 chip if custom firmware behavior is ever needed. Power comes through a simple 5V VCC/GND connection via a 2.54mm pin socket, and the board itself is compact at 36 x 25 x 12mm.

One important note from the listing: for accurate readings, the object being measured should be at least 0.5 square meters in surface area, smooth, and highly reflective, since ultrasonic sensing depends on a clean echo bouncing back, and a small, soft, or irregularly shaped object can give inconsistent readings regardless of how good the control board itself is. The HC-SR04 sensor itself is not included and needs to be purchased separately. Anyone wanting a quick, standalone way to test or display HC-SR04 readings without wiring up a full microcontroller setup will find this control board a genuinely useful bench tool.