What is an ultrasonic sensor?

An ultrasonic sensor is an instrument that measures the space to an object using ultrasonic sound waves.

An ultrasonic sensor uses a transducer to send and receive ultrasonic pulses that relay back information about an object’s proximity.

High-frequency sound waves reflect from boundaries to supply distinct echo patterns.

How Ultrasonic Sensors Work.

Ultrasonic sensors work by sending out an acoustic wave at a frequency above the range of human hearing. The transducer of the sensor acts as a microphone to receive and send the ultrasonic sound. Our ultrasonic sensors, like many others, use one transducer to send a pulse and to receive the echo. The sensor determines the space to a target by measuring time lapses between the sending and receiving of the ultrasonic pulse.

The projects are available at: Ultrasonic Distance Sensor


Here’s a list of some of the HC-SR04 ultrasonic sensor features and specs:

  • Power Supply: +5V DC
  • Resolution: 0.3 cm
  • Effectual Angle: <15°
  • Working Current: 15mA
  • Quiescent Current: <2mA
  • Measuring Angle: 30 degree
  • Trigger Input Pulse width: 10uS
  • Dimension: 45mm x 20mm x 15mm
  • Ranging Distance : 2cm – 400 cm/1″ – 13ft

How does it Work?

The ultrasonic sensor works on the principle of SONAR and RADAR system which is employed to work out space to an object. An ultrasonic sensor generates the high-frequency sound (ultrasound) waves. When this ultrasound hits the thing, it reflects as echo which is sensed by the receiver Provide TRIGGER signal, a minimum of 10μS High Level (5V) pulse. The module will automatically transmit eight 40KHz ultrasonic bursts. If there’s an obstacle ahead of the module, it’ll reflect the ultrasonic burst. 

If the signal is back, the ECHO output of the sensor is going to be during a HIGH state (5V) for the duration of your time taken for sending and receiving ultrasonic bursts. Pulse width ranges from about 150μS to 25mS and if no obstacle is detected, the echo pulse width is going to be about 38ms.


HC-SR04 Ultrasonic Sensor Pinout


  • VCC: +5VDC
  • Trig: Trigger (INPUT)
  • Echo: Echo (OUTPUT)
  • GND: GND

Ultrasonic Sensors are best used in the non-contact detection of:

  • Level
  • Position
  • Distance
  • Presence