An ultrasonic radar is one of the most satisfying beginner Arduino projects: a sensor sweeps back and forth like a tiny radar dish, and nearby objects appear on a display in real time. It teaches distance sensing, servo control and display programming in a single afternoon build, and it looks great on a desk or a science-fair table.
How It Works
An HC-SR04 ultrasonic sensor sits on top of a small servo motor. The servo sweeps the sensor slowly from one side to the other while the sensor sends out sound pulses and listens for echoes. The Arduino converts each echo time into a distance, pairs it with the current servo angle, and draws a simple radar-style plot on an OLED display, with closer objects shown nearer the centre.
Components Required
- Arduino Uno or Nano board
- HC-SR04 ultrasonic distance sensor
- SG90 micro servo motor
- 0.96 inch OLED display (I2C)
- Small buzzer (optional, for a proximity beep)
- USB cable, jumper wires, breadboard
- Cardboard or a small mount to hold the sensor on the servo
Circuit Connections
- HC-SR04 Trig to Arduino digital pin 9, Echo to digital pin 10, VCC to 5V, GND to GND.
- Servo signal wire to digital pin 11, power to 5V, ground to GND.
- OLED SDA to A4, SCL to A5 on an Uno (check your board's I2C pins if you use a Nano).
- Buzzer positive to digital pin 6 through a resistor, negative to GND, if you add the optional beep.
- Power the servo from the Arduino 5V pin only for this small SG90; larger servos need their own supply.
Build Steps
1. Mount the ultrasonic sensor on the servo horn with a small cardboard bracket, so it points forward and sweeps freely.
2. Wire the circuit as listed and upload a sweep program that moves the servo in small steps and records a distance at each step.
3. Draw the radar view on the OLED: a sweeping line at the current angle, and a dot wherever an object is detected.
4. Add the optional buzzer so it beeps faster as an object gets closer.
5. Test with objects at different distances — a book, a bottle, your hand — and check the display matches what you see.
Troubleshooting
- Readings stuck at one value: check the Trig and Echo wiring, and make sure the sensor is not facing a soft surface like a curtain, which absorbs sound.
- Servo jittering: check the power supply and keep the servo wires short; a weak USB port can cause twitching.
- Display blank: confirm the OLED I2C address in your code, and check SDA and SCL are not swapped.
- Noisy distance jumps: add a short pause between readings and average two or three readings per angle.
Going Further
Once the basic radar works, try logging distances to a computer over serial, adding coloured LEDs for near, medium and far zones, or mounting the whole unit on a small robot chassis. The same sweeping-sensor idea is the starting point for obstacle-avoiding robots.
What will your radar guard first — a desk, a doorway, or a model car park? Tell us in the comments.
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