EMBEDDED SYSTEMS / SENSING · PERSONAL PROJECT
A Wi-Fi-enabled ultrasonic scanning demonstrator built around an ESP32, HC-SR04 sensor, SG90 servo and 0.96-inch OLED. The servo sweeps through 180° while the ESP32 measures distance and publishes live readings to a browser dashboard hosted on the microcontroller.
01 / PROJECT BRIEF
Develop a low-cost ultrasonic scanner that can rotate a sensor, measure distances at successive commanded angles and present the latest measurement locally and remotely. The system was first exercised in Wokwi, then transferred to a physical breadboard assembly.
Terminology: This is an ultrasonic scanning demonstrator, not a radio-frequency radar. The servo angle is commanded in open loop rather than measured with an angle encoder.
02 / SYSTEM ARCHITECTURE
ESP32 commands the SG90 from 0° to 180°, reverses, then repeats.
The HC-SR04 produces a return pulse used to calculate round-trip distance.
The OLED displays the latest angle, distance and scan/object state.
The ESP32 serves a dashboard; its /data endpoint supplies updated scan values.
The browser repeatedly requests measurement data and redraws the polar display. The displayed angle is the commanded servo position, not independently verified angular feedback.
Distance = (echo pulse duration × speed of sound) / 2
The division by two accounts for the outward and return travel of the sound pulse.03 / ENGINEERING DECISIONS
An 18650 cell with MT3608 boost converter supplied the SG90 and HC-SR04, rather than drawing servo current through the ESP32's 3.3 V rail. The converter output was adjusted to approximately 5 V using a multimeter before powering the hardware.
The ESP32 was powered through USB while its GPIO signals controlled separately powered devices. Common ground connected the controller and external supply so signal levels had a consistent reference.
The HC-SR04 Echo output operates at 5 V. A 1 kΩ/2 kΩ resistor divider was used before ESP32 GPIO 18, producing approximately 3.33 V for a nominal 5 V high signal.
Wokwi enabled testing of sensor interfaces, servo sequencing, OLED layout and web-dashboard behaviour before connecting the real wiring and power supply.
The final browser plot displayed 0–100 cm rather than the earlier 0–400 cm range to suit the available test area. This was a display adjustment, not a verified improvement in sensor resolution.
The HC-SR04 used a temporary taped mount while testing. A printed sensor bracket and more compact enclosure were left for a later mechanical revision.
04 / ELECTRICAL DESIGN
| Component | Connection / role | Selection rationale |
|---|---|---|
| ESP32 Dev Board | Controller and Wi-Fi web server | Integrated wireless connectivity and sufficient GPIO |
| HC-SR04 ultrasonic sensor | TRIG GPIO 5 · ECHO GPIO 18 via divider | Low-cost short-range distance acquisition |
| SG90 servo | Signal GPIO 13 · external 5 V supply | Rotates the lightweight sensing module |
| 0.96-inch I²C OLED | SDA GPIO 21 · SCL GPIO 22 · 3.3 V | Live feedback without a separate browser |
| MT3608 boost converter | 18650 battery to ~5 V rail | Separate sensor/servo power path |
| 1 kΩ / 2 kΩ divider | Echo voltage level shifting | Reduces nominal 5 V Echo pulse to ~3.33 V |
ESP32 USB → ESP32 + OLED (3.3 V)
18650 → MT3608 (~5 V) → SG90 + HC-SR04
All subsystem grounds joined; HC-SR04 Echo signal enters the ESP32 through a voltage divider.
05 / FIRMWARE
The firmware coordinates four functions: servo sweep, ultrasonic measurement, OLED updates and serving live values over Wi-Fi. The dashboard polls the ESP32's /data endpoint and uses the returned values to refresh the display.
Sweep function from the original project documentation:
void sweepRadar() {
angle += direction;
if (angle >= 180) direction = -1;
if (angle <= 0) direction = 1;
radarServo.write(angle);
currentDistance = getDistance();
currentAngle = angle;
}The function reverses direction at the end of each scan and associates the distance measurement with the latest commanded angle. Mechanical backlash, settling time and timing delays were not independently characterized.
06 / TESTING
Simulated the ESP32, ultrasonic sensor, servo and OLED to verify the basic wiring and interface logic before assembling the physical circuit.
Set the MT3608 output to approximately 5 V using a multimeter. A loose power connection was diagnosed after the servo/sensor rail stopped functioning.
Observed the SG90 sweeping the sensor, the HC-SR04 responding to objects and the OLED displaying live readings.
Connected to the ESP32 dashboard via Wi-Fi and observed live angle, distance and detection updates in the browser.
Verified scope: The original project documents a functioning servo sweep, ultrasonic response, OLED display and live web dashboard. It does not supply calibrated range-error measurements, angular repeatability statistics, response-time traces or power-consumption logs. These are not claimed.
07 / REFLECTION
The main practical issues were electrical rather than firmware-related: correct 5 V delivery, a reliable shared ground, a loose power wire and protecting the 3.3 V ESP32 input from a 5 V Echo signal. Testing in Wokwi reduced uncertainty before energising the breadboard hardware.
Future improvements include replacing the taped sensor mount with a 3D-printed bracket, shortening the wiring, adding a compact enclosure, logging scans, and measuring distance error and servo-angle repeatability. These improvements are planned rather than completed.