Ultrasonic sensor for measuring
distance: This
circuit is developed by interfacing ultrasonic sensor“HC-SR04” with AVR
microcontroller. This sensor uses a technique called “ECHO” which is something
you get when sound reflects back after striking with a surface. We know that
sound vibrations cannot penetrate through solids. So what happens is, when a
source of sound generates vibrations they travel through air at a speed of 220
meters per second. These vibrations when they meet our ear we describe them as
sound. As said earlier these vibrations cannot go through solid, so when they strike
with a surface like wall, they are reflected back at the same speed to the
source, which is called echo.
Ultrasonic
sensor “HC-SR04” provides an output signal proportional to distance based on
the echo. The sensor here generates a sound vibration in ultrasonic range upon
giving a trigger, after that it waits for the sound vibration to return. Now
based on the parameters, sound speed (220m/s) and time taken for the echo to
reach the source, it provides output pulse proportional to distance. As shown
in figure, at first we need to initiate the sensor for measuring distance, that
is a HIGH logic signal at trigger pin of sensor for more than 10mS, after that a sound vibration
is sent by sensor, after a echo, the sensor provides a signal at the output pin
whose width is proportional to distance between source and obstacle.
This
distance is calculate as, distance (in cm) = width of pulse output (in mS) / 58. Here the width of the
signal must be taken in multiple of mS (micro
second or 10^-6).
Expt-1
1.
Title: Distance Measurement using Ultrasonic sensor
HC-SR04.
2.
Components
required:
Sl. No.
|
Category
|
Item name/value
|
Quantity
|
Remarks
|
1
|
IC
|
ATMEGA32
|
1
|
|
Power supply
|
5v
|
|||
3
|
Resistor
|
10K
|
2
|
|
4
|
Display
|
JHD_162ALCD (16x2LCD)
|
1
|
|
5
|
Capacitor
|
0.1uf
|
2
|
|
6
|
22pf
|
2
|
||
7
|
1000uf, 24Volt
|
1
|
||
8
|
Crystal Oscillator
|
16MHz
|
1
|
|
9
|
USD sensor
|
HC-SR04
|
1
|
|
10
|
PROGRAMMER
|
AVR-ISP
|
1
|
3.
Procedure
to code:
a. write
header to enable data flow control over pins
b. assign
controller crystal frequency attached
c.
include header to enable delay
function in program
d. define
“enable” to 5 pin of PORTD, since it Is connected to LCD enable pin
e.
define “registerselection” to 6
pin of PORTD, since is connected to LCD RS pin
f.
declare interger 'pulse' to
access all though the program
g.
declare interger 'i' to access
all though the program
h. set
portB as output pins
i.
giving delay of 50ms
j.
Taking portD as output except D2
k. enable
interrupt0
l.
set interrupt triggering logic
change
m. store
digital output
n. displaying
digital output as temperature in 16*2 lcd
o. Clear
Screen \
p. tell
lcd we are using 8bit command /data mode
q. LCD
SCREEN ON and courser blinking
r.
enable global interrupts
s.
Under infinite loop
i.
trigger the sensor for 15usec
ii.
get the distance based on formula
on introduction
iii.
display name
iv.
shift cursor to 1 shell of second
line
v.
display name
vi.
send command for putting variable
number in LCD(variable number, in which character to send_a_string (SHOWA);
vii.
tell the display to show
character(replaced by variable number) after positioning send_a_string
("cm ")
viii.
retun to first line first shell
t.
interrupt service routine when
there is a change in logic level at INT0
u. when
logic from HIGH to LOW
v. disabling
counter
w. count
memory is updated to integer
x. resetting
the counter memory
y. when
logic change from LOW to HIGH
z.
enable counter
4.
Code:
/*
C Program for Distance Measurement using Ultrasonic Sensor and AVR
Microocntroller
*/
#ifndef F_CPU
#define F_CPU 16000000UL
#endif
#include <avr/io.h>
#include <avr/interrupt.h>
//#define F_CPU 1000000
#include <util/delay.h>
#include <stdlib.h>
#define enable 5
#define registerselection 6
void send_a_command(unsigned char command);
void send_a_character(unsigned char character);
void send_a_string(char *string_of_characters);
static volatile int pulse = 0;
static volatile int i = 0;
int main(void)
{
//DDRA = 0xFF;
DDRB = 0xFF;
DDRD = 0b11111011;
_delay_ms(50);
MCUCR|=(1<<ISC00);
GICR|=(1<<INT0);
TCCR1A = 0;
uint16_t COUNTA = 0;
char SHOWA [16];
send_a_command(0x01); //Clear Screen 0x01 = 00000001
_delay_ms(50);
send_a_command(0x38);
_delay_ms(50);
send_a_command(0b00001111);
_delay_ms(50);
sei();
while(1)
{
_delay_ms(500);
PORTD|=(1<<PIND0);
_delay_us(15);
PORTD &=~(1<<PIND0);
COUNTA = pulse/(58*16);
send_a_string ("
USDM ");
send_a_command(0x80 + 0x40 + 0);
send_a_string ("DISTANCE=");
if (COUNTA<30)
{
itoa(COUNTA,SHOWA,10);
send_a_string(SHOWA);
send_a_string ("cm
");
_delay_ms(100);
}
else {send_a_string ("Undef");
_delay_ms(100);}
send_a_command(0x80 + 0);
}
}
ISR(INT0_vect)
{
if (i==1)
{
TCCR1B=0;
pulse=TCNT1;
TCNT1=0;
i=0;
}
if (i==0)
{
TCCR1B|=(1<<CS10);
i=1;
}
}
void send_a_command(unsigned char command)
{
PORTB = command;
PORTD &= ~ (1<<registerselection);
PORTD |= 1<<enable;
_delay_ms(8);
PORTD &= ~1<<enable;
PORTB = 0;
}
void send_a_character(unsigned char character)
{
PORTB = character;
PORTD |= 1<<registerselection;
PORTD |= 1<<enable;
_delay_ms(8);
PORTD &= ~1<<enable;
PORTB = 0;
}
void send_a_string(char *string_of_characters)
{
while(*string_of_characters > 0)
{
send_a_character(*string_of_characters++);
}
}
5.
Simulation:
