Ultrasonic Range Finder Using At Mega 8515

8/3/2019 Ultrasonic Range Finder Using At Mega 8515

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Ultrasonic range finder using ATMega8515

This project is used to measure the distance using ultrasonic sensors. The ultrasonic

signal passes through the atmosphere to a barrier, which we want to measure the distance.Part of this signal is reflected and travels back to the receiver. The time delay between

sending and receiving signals are then determined by distance barriers.

The device was designed as a parking assistant for the car. It will help the driver while

reversing the car to measure the amount of free space behind the vehicle. It is possible todownload for this device are two types of software on the MCU. The first version is

intended for parking assistant. After activating the measurement device measures the

distance still to shutdown and it shows on the LCD. The second version is designed for manual distance measurement. After activating the device measures the distance and

show it on LCD. For further measurements you need to activate it again with the switch.

Circuit Diagram



Operation

40Khz ultrasonic sensors are used. Microcontroller that controls the distance

measurement is the Atmel AVR Mega8515. Measured distance is displayed on the

display 2x16 characters. The device has two buttons. S2 button activates or deactivates ameasurement button S1 is controlled backlight. The device also includes a connector for

connecting the programmer SV1 via ISP.



When activated, the microcontroller will generate measurements using 8bit timer port B0

frequency 40kHz, which passes through inverters for amplifying the current and used to

drive the ultrasonic transmitter that will broadcast the ultrasonic waves at 40khz.Simultaneously with the activation of the posting run 16bit timer that measures time by

receiving the reflected signal. Sending a signal spread environment. After hitting the

barrier is part of it is reflected and returns back to the sensor. The reflected signal isdetected by the receiver, amplified in amplifier. Received signal is brought to an internal

analog comparator of the microcontroller, in which income is due to rollover. At this

point, the transmission is stopped, but mainly stops counting the time reception of reflected signals. 16bit timer is set so that the counting pulses 1?s. Measurement is treated

in a way where there is no reception, there is a 16-bit counter overflows (after 65ms) and

sending a timing stops. The display shows the inscription "out of reach". Further

measurements are re-activated by pressing button S2. When receiving the reflected signaland the subsequent completion of counting time is 1?s counted the number of samples

stored in the variable register, and timer is reset. Variable that contains the number of

time samples must be multiplied with a constant length in order to display the measured

distance.

When multiplied by the number of variables and sample length of time brings up a

constant distance to the obstacle in centimeters. The result is rounded to one decimal

place. The circuit also uses an LED. It starts flashing at a distance of less than obstaclesto 50cm.

Before the first (after production equipment) measurement it is needed to set the

reference voltage for comparator. This is done by the variable resistance R5. We will link

connector JP2. By the meter set adjustment mode. The transmitter will continue to broadcast. Reference voltage to set the size to analog comparator to the maximum

measured distance. Flip LED signals. When sufficient income reflected signal to flip andLED lights up. If one sensor , the LED should extinguish. Open the JP2 connector andthe sensor is ready for measurement. Resistance trimmer R2 is used to adjust the contrast

of characters on the LCD.

The disadvantage of this simple rangefinder is the speed of ultrasonic sound varies in air

due to temperature change.

The speed of sound in air at different temperatures

Temperature Speed

-20°C 319,3 m/s

0°C 331,6 m/s

5°C 334,5 m/s

10°C 337,5 m/s

15°C 340,6 m/s



20°C 343,8 m/s

25°C 346,3 m/s

40°C 355,3 m/s

60°C 366,5 m/s80°C 377,5 m/s

The rangefinder has a length constant calculated for a temperature of 25°C. For moreaccurate measurements it sis necessary to add a thermometer. So before each

measurement, first measure air temperature, and choose the appropriate length constant.

The speed will also get changed with variable pressure. This change is not as great as inthe case of temperature change.

Ultrasonic Range Finder Using At Mega 8515

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