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Ultrasonic sensor basics | Distance sensor working

This page describes basic function of Ultrasonic sensor. It mentions Ultrasonic sensor construction and working of Ultrasonic sensor. It is used as distance sensor.

Definition: The ultrasonic sensor is a transducer which converts electrical energy into sound waves and viceversa. These sound waves fall above the normal range of human hearing and hence it is known as ultrasonic waves. These type of waves are above the frequency of about 18000 Hz.

Ultrasonic Sensor or distance sensor construction and working

Ultrasonic Sensor

• There are two main parts in the sensor viz. transmitter and receiver.
• The transmitter part converts electrical energy into sound and transmits it.
• The receiver part receives the echo and turn this received sound waves into electrical energy.
• This returned echo is measured and used for distance calculation by the ultrasonic sensor. Basically this sensor calculates time interval between signal transmission and reception of echo and determines the distance of the object from the sensor. As this sensor is used for distance measurement it is known as distance sensor.
• Piezoelectric crystals are used in the ultrasonic sensor construction due to the fact that these crystals oscillate at higher range of frequencies.

ultrasonic sensor pin diagram

The figure-2 depicts pin diagram of a ultrasonic sensor or distance sensor. As shown there are four pins viz. +5V (Vcc pin), GND, Trigger pin and Echo pin.

Ultrasonic sensor signals

Let us understand step by step working of ultrasonic sensor.
• STEP-1: Make 'TRIGGER' pin of sensor high for some duration (say 10µs). This will initiate sensor cycle.
• STEP-2: Eight pulses of 40 KHz are transmitted from transmitter part of sensor. After this is done, 'ECHO' pin goes high from low state.
• STEP-3: After the transmission, transmitted signal gets reflected from the nearby object and returns back to the sensor.
• STEP-4: When the ultrasonic sensor detects reflected wave, 'ECHO' pin of sensor goes low.
• STEP-5:The time duration when ECHO pin is high will provide distance between sensor and detected object.
• STEP-6: The ultrasonic sensor is programmed in such a way that if no object is found then ECHO pin remains high for 38ms and will go low again.

Technical specifications of Ultrasonic Sensor

Following are the typical specifications of a ultrasonic sensor.
• Nominal Frequency output: 40 KHz
• Coverare range: 0.2 to 6 meters
• Receiver sensitivity: -67 dBm
• Sound pressure level: 112 dB (minimum)
• Maximum voltage input: 20 V(rms)

Ultrasonic or distance sensor applications

Following are the applications of Ultrasonic or distance sensor:
• It is used in automatic car parking system.
• It is used in humanoid robot design.


Also refer IoT compliant sensors which includes ambient light sensor, optical sensor, gesture sensor, proximity sensor, touch sensor, fingerprint sensor etc.
Refer Sensors and transducers article which covers types, basic functions and provide links to sensors and transducers. It include temperature sensor, humidity sensor, strain sensor, proximity or occupancy sensor, force or load sensor, voltage and current sensor, pressure sensor, speed sensor, resistance sensor, power sensor, level sensor, event or state sensor etc.

Sensors and Transducers Related Links

Proximity Sensor
Occupancy Sensor vs Motion Sensor
LVDT and RVDT sensor
Position, displacement and level sensor
force sensor and strain sensor
temperature sensor
pressure sensor
Humidity sensor
MEMS sensor
Touch sensor
Haptic sensor
Wireless sensor

RF and Wireless Terminologies

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