1. IIST
DIGITAL ANEMOMETER
Kosuru Sai Malleswar
Harmeet Singh
Rajil Ramesh A.
An instrument that can measure both the speed and the direction of the wind flow

2. Introduction
An anemometer is a device for measuring wind speed. Coupled with a weather vane which
indicates the direction of the wind, it forms a complete setup for describing the wind at any given
geographical location.
There are a variety of anemometers available currently which are classified on the basis of
their operating principle. Cup anemometers, Windmill anemometers, Hot-wire anemometers, Laser
Doppler anemometers, Sonic anemometers, Ping-pong ball anemometer and Acoustic Resonance
Anemometers are a few to name. Two-dimensional (wind speed and wind direction) anemometers
are used in applications such as weather stations, ship navigation, wind turbines, aviation and
weather buoys.
Our Design
The anemometer that we have made as a part of this event is of cup type. It consists of four
hemispherical cups each mounted on one end of four horizontal arms, which in turn were mounted
at equal angles to each other on a vertical shaft. On an anemometer with four cups it is easy to see
that since the cups are arranged symmetrically on the end of the arms, the wind always has the
hollow of one cup presented to it and is blowing on the back of the cup on the opposite end of the
cross. Due to the shape of the cups, more pressure and hence more force is exerted on the concave
surface of the cups as compared to the convex surface resulting in an unbalanced torque causing
the shaft to rotate. The air flow past the cups in any horizontal direction rotated the shaft in a
manner that was proportional to the wind speed. We have used a DC motor in place of a dynamo
to convert the shaft rotation to equivalent voltage.
For measuring the angle of wind, we have used a wind wane. The design of a wind vane is
such that the center of gravity is directly over the pivotal axis, so that the pointer can move freely
on its axis, but the surface area is unequally divided. The side with the larger surface area is blown
away from the turdle, so that the smaller side, with the pointer, is pivoted to face into the wind
direction. Most wind vanes have directional markers beneath the arrow, aligned with the
geographic directions. In the present design, we have used a simple single turn resistive
potentiometer attached to the wind wane as our sensor. The voltage at wiper point is clearly
proportional to the angle of the rotating dial.
Once we have the sensors in place, we can calibrate them to obtain the true wind speed and
direction. By giving the analog voltage outputs of these sensors to a microcontroller after some
signal conditioning, we can convert them to digital format for displaying on LCD.

3. Block Diagram
Figure 1: Block diagram of anemometer and wind direction measurement setup
Signal Processing unit
The voltage produced by the motor in generator mode is proportional to the velocity of the
rotating shaft which is proportional to the wind speed. So we made a plot of wind speed versus the
voltage produced. From the graph, we found the offset and the gain. According to these results,
we programmed ATMEGA128 Microcontroller to read the voltage through 10 bit Analog to
Digital Converter (ADC) units, perform scaling operations and display the speed value on 2X16
LCD Module. The supply voltage to the Microcontroller is 5V.
The voltage corresponding to the angle is indicated by the wiper arm of potentiometer. This
is read by another ADC channel of Microcontroller and scaled to obtain the angle and display on
LCD.
Figure 2: Signal Conditioning unit

4. Conclusion
Anemometer which can measure wind speeds from 2 m/s to 22 m/s with an accuracy of
0.05 m/s along with the set up for measuring the wind direction based on the reference direction
with a resolution of 0.3516 degree has been made. This system was connected with
Microcontroller unit to display the speed and the angle on LCD.
Code for measuring speed and angle and displaying on LCD
#include <avr/io.h>
#define F_CPU 14.7456e6
#include <avr/interrupt.h>
#include <util/delay.h>
#include "lcd.h"
#define adc_delay 40
#define samples 5
uint16_t adc_reading;
float c,fr;
float speed,angle;
uint8_t count=0;
uint16_t adc_read(unsigned char Ch)
{
uint16_t res;
Ch = Ch & 0x07;
ADMUX= 0x00| Ch;
ADCSRA = ADCSRA | 0x40;

5. while((ADCSRA&0x10)==0);
res = (uint16_t)ADCL;
res|= (((uint16_t)ADCH)<<8);
ADCSRA = ADCSRA|0x10;
return res;
}
void lcd_print_float(uint8_t row, uint8_t col,float value)
{
float fract;
lcd_print(row,col,(int)value,3);
lcd_cursor(row,col+3);lcd_wr_char('.');
fract=(int)(1000*(value-(int)value));
lcd_print(row,col+4,fract,3);
}
//Main Function
int main(void)
{
DDRC = DDRC | 0xF7;
PORTC = PORTC & 0x80;
ADCSRA = 0x00;
ADMUX = 0x00;
ACSR = 0x80;
ADCSRA = 0x86;

6. lcd_set_4bit();lcd_init();
lcd_string(" SPEED | ANGLE ");
lcd_cursor(2,8);lcd_wr_char('|');
while(1)
{
adc_reading=adc_read(0); c=(float)adc_reading; c=c*5000/1024;
if(c>70)
{
speed=c*0.0093; speed+=3.0846;
}
else
{
speed=0.000;
}
lcd_print_float(2,1,speed); _delay_ms(100);
adc_reading=0;
for(count=0;count<5;count++)
{
adc_reading+=adc_read(2); _delay_ms(100);
}
angle=(float)adc_reading; angle/=5;
angle=angle*360/1024;
lcd_print_float(2,9,angle);
}
}