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HC-SR04 Ultrasonic Distance Sensor Module


The HC SR04 Ultrasonic Distance Sensor is the most cost-effective solution for applications where precision range-finding, 5V operation and low-cost are needed. The SR04 Range Finder has only four pins and can be used with two Digital I/O pins.

The SR04 Distance Sensor is very easy to use. Ranging is started by applying a 10us wide (or longer) pulse on the "Trigger" pin. The "Echo" pin goes high the SR04 has detected the return echo from the reflecting surface. 

The distance is determined by the speed of sound and the time between the Trigger and Echo pulses. The distance travelled is twice the distace from the sensor to the reflecting surface, once to the surface and once from the reflacting surface back to the receiver on the SR04. So the distance can be calculated as:

Distance = 0.5 * EchoTime * Speed Of Sound

The speed of sound is about 330 meters/s or 33000 cm/s in metric units and 12870 Inch/s in Imperial units. See for more details and better formulas.

This popular ultrasonic distance sensor provides stable and accurate distance measurements from 2cm to 450cm. It has a focus of less than 15 degrees and an accuracy of about 2mm,This particular sensor sends out an ultrasonic sound that has a frequency of about 40 kHz.


  • Operating Voltage: 5V(DC).
  • Static Current: Less than 2mA.
  • Output Signal: Electric frequency signal, high level 5V, low level 0V.
  • Sensor Angle: Not more than 15 degrees.
  • Detection Distance: 2cm-450cm.
  • High Precision: Up to 0.3cm.
  • Input Trigger Signal: 10us TTL impulse.
  • Echo Signal : output TTL PWL signal.

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