ultrasonic sensor HC-SR04 HCSR04 distance meter for arduino raspberry pi

ultrasonic sensor HC-SR04 HCSR04 distance meter for arduino raspberry pi - The sensor that is able to measure distances is stable and accurate compared to the SRF05, SRF02 modules, the accuracy is up to 0.3cm. 

The blind spot only occurs at a super close distance of 2cm.

The HC-SR04 proximity sensor module is a highly accurate distance meter. It consists of two transducers, one of which functions as a wave 
transmitter and the other functions as a wave receiver. This module generates high frequency sound waves (40kHz).
Interfaces:
1. VCC positive 5V DC
2. Trig control part
3. Echo receiver
4. Gnd ground
Specification:
> Voltage: 5V DC
> Quiescent Current 2mA
Effective measuring angle < 15
> Effective measuring distance 2~450cm
> Measuring error tolerance: 0.3cm
> Signal output: 5V DC HIGH; 0V DC LOW

Procedure:
1. The IO port gets a high signal command for 10us or more
2. This sensor module then transmits 8x 40kHz sound waves and automatically monitors the waves returning due to reflection
3. When the waveform is back, the IO port outputs a HIGH signal. The time difference between the command and the returning ultrasonic wave can 
be measured as a distance. According to the opinion of one of our customers "The length of time the ECHO pin emits a HIGH (Low-High-Low) signal is 
proportional to the distance"
The formula:
Distance = (time x speed of sound) / 2
Where the speed of sound is known = 340 m/s (normal standard, except over mountains & low temperatures)