Ultrasonic sensors

Ultrasonic sensors work on a principle similar to radar or sonar which evaluates attributes of a
target by interpreting the echoes from radio or sound waves respectively.HC-SR04 Ultrasonic
Distance Sensor is a popular and low cost solution for non-contact distance measurement
function. It is able to measure distances from 2cm to 400cm with an accuracy of about 3mm.
This module includes ultrasonic transmitter, ultrasonic receiver and its control circuit.

HC-SR04 module has 4 pins:

1. VCC 5V +ve of the power supply

2. TRIG Trigger Pin

3. ECHO Echo Pin

4. GND -ve of the power supply

WORKING PRINCIPLE

Sensor measures the obstacle in the front travelling path. TRIG and ECHO pins can be used to
interface ultrasonic module with a microcontroller unit. Provide TRIGGER signal, at least 10μS
High Level (5V) pulse. The module will automatically transmit eight 40 KHz ultrasonic burst. If
there is an obstacle in-front of the module, it will reflect the ultrasonic burst. If the signal is back,
ECHO output of the sensor will be in HIGH state for duration of time taken for sending and
receiving ultrasonic burst. Pulse width ranges from about 150μS to 25mS and if no obstacle is
detected, the echo pulse width will be about 38ms.To obtain the distance, measure the width of
Echo pin. If the obstacle is detected, the microcontroller sends a signal to Relay switches which
operate Vibrator. It also detects Panic Switches Input (Emergency Help Switches) and sends
SMS to user Family member with User’s GPS location. Here we are using the GSM module for
sending the coordinates of blind man on mobile phone via message. GPS sends the coordinates
continuously in form of string.