Ultrasonic & Distance Sensors

Distance sensors let robots avoid walls, bins report how full they are, and tanks report their water level. Three types cover most projects.

  • The HC-SR04 ultrasonic sensor sends a 40 kHz ping and times the echo. Distance in centimetres is the echo pulse width divided by 58, with no library needed. Readings past about 3 m get unreliable.
  • Time-of-flight (ToF) sensors such as the VL53L0X and VL53L1X time reflected laser light. They give fine, millimetre-level distance over I2C at shorter range, but bright ambient light can roughly halve their range.
  • IR obstacle sensors only tell you whether something is within range, with no distance number.

How to choose:

  • Pick ultrasonic for cheap, general distance.
  • Pick ToF for precise short range or a narrow beam.
  • Pick IR for simple "is something there?" triggers.

All of them work with Arduino and ESP32. The HC-SR04's Echo pin outputs 5V, so on a 3.3V board such as the ESP32 put a voltage divider on Echo before it reaches the GPIO.

Frequently asked questions

How do I convert HC-SR04 time to distance?

Divide the echo pulse width in microseconds by 58 to get centimetres.

Can I connect an HC-SR04 to an ESP32?

Yes, but add a voltage divider on Echo. It outputs 5V, and ESP32 pins are 3.3V only.

Why is my ToF sensor's range shorter outdoors?

Bright ambient light can roughly halve a VL53L0X's range compared with darkness.

Does an IR obstacle sensor measure distance?

No. It switches when something is within range. Use ultrasonic or ToF for a number.

Guides

Reference pages on soldr.ai

More guides on soldr.ai

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