Rpm Counter Using Micro Controller

| RPM Counter Using Microcontroller AT89C4051 1

RPM COUNTER USING MICROCONTROLLER

AT89C4051

1. WHAT IS RPM COUNTER

An instrument that measures angular speed, as that of a rotating

shaft. The measurement may be in revolutions over an

independently measured time interval, as in a revolution counter,

or it may be directly in revolutions per minute. The instrument

may also indicate the average speed over a time interval or the instantaneous speed. RPM

Counters are used for direct measurement of angular speed and as elements of control

systems to furnish a signal as a function of angular speed.

2. REVOLUTIONS PER MINUTE

Revolutions per minute (abbreviated rpm, RPM, r/min, or r·min−1

) is a measure of the

frequency of a rotation. It annotates the number of full rotations completed in one minute

around a fixed axis. It is used as a measure of rotational speed of a mechanical component.

Standards organizations generally recommend the symbol r/min, which is more consistent

with the general use of unit symbols.

2.1 International System of Units

According to the International System of Units (SI), rpm is not a unit. This is because

Revolutions is a semantic annotation rather than a unit. The annotation is instead done in the

subscript of the formula sign if needed. Because of the measured physical quantity, the

formula sign has to be f for (rotational) frequency and ω or Ω for angular velocity. The

corresponding basic SI unit is s−1

or Hz. When measuring angular speed, rad·s−1

can also be

used as unit.


Even though angular velocity, angular frequency and hertz all have the dimensions of 1/s,

angular velocity and angular frequency are not expressed in hertz, but rather in an appropriate

angular unit such as radians per second. Thus a disc rotating at 60 revolutions per minute

(rpm) is said to be rotating at either 2π rad/s or 1 Hz, where the former measures the angular

velocity and latter reflects the number of complete revolutions per second. The conversion

between a frequency f measured in hertz and an angular velocity ω measured in radians per

second are:

ω=2*π*f and f=ω/(2*π)

rpm to Hz

2400*2*3.14=15072 rad/min

15072/60=251.2 rad/s

(1800*2*3.14)/60=188.4 rad/s

(3300*2*3.14)/60=345.4 rad/s

3. INTRODUCTION

Counting the revolutions per minute (RPM) of motors determining the motor speed is

essential in the field of industrial automation. It is useful especially for closed-loop control

systems where proper action can be taken in case the actual RPM deviates from the set RPM.

This project is based on micro-controller AT89C4051 that measures and shows on an LCD

the RPM of a running motor. Using a proper transducer, first the rotations of the motor are

converted into pulses. The generated pulses are counted by the micro controller for a fixed

time (say, one second). The count is multiplied by a factor to get the exact RPM and then

displayed; if time is one second, the factor is 60.

4. CIRCUIT DESCRIPTION

Fig. 1 shows the block diagram of the RPM counter based on AT89C4051 microcontroller

that generates pulses for every rotation of the motor, counts them and shows on the LCD.

On a fixed base, there is a laser source on one side and the combination of a light-dependent

resistor (LDR), pulse generator, microcontroller and LCD on the other side. Both the


arrangements are housed in separate wooden cabinets such that the laser beam falls directly

on the LDR. The motor is placed on top of the laser source. A slotted wheel is attached to the

motor shaft. The wheel is so bit that it can interrupt the laser beam falling on the LDR.

As the motor rotates, the slotted wheel also rotates. The laser beam falls on the LDR

whenever the slot aligns with the laser beam and LDR, producing one pulse. Thus the

rotations of the motor are converted into pulses that can be counted by the program in the

microcontroller. Pulses are counted for one second. The pulse count is multiplied by 60

(because 1 RPM = 60 RPS) and finally shown on the LCD.

Fig. 2 shows the circuit of the RPM meter. It comprises microcontroller AT89C4051, timer

NE555, LCD module (16x2 line) and a few discrete components. Timer NE555 is configured

as a mono-stable multi-vibrator whose time period depends upon the combination of resistor

R1 and capacitor C1. Trigger pin 2 of NE555 is pulled high via resistor R2. The LDR is

connected along with resistor R2 to pin 2 of NE555 such that when the laser light falls on the

LDR, pin 2 goes low to trigger NE555.

The output form pin 3 of NE555 is inverted by transistor T1 and fed to port pins P3.3 and

P3.4 of the micro controller. LED2 is connected to port pin P3.0 (pin 2) of the

microcontroller. Data pins D0 through D7 of the LCD are connected to port pins P1.0

through P1.7 of the microcontroller, respectively. Control pins E, RS and R/W of the LCD


are connected to port pins P3.2, P3.5 and P3.7, respectively. A 12MHz crystal connected

between pins 4 and 5 of the microcontroller, along with two 22pF capacitors C4 and C5,

generates the basic clock frequency. Power-on reset is derived with the combination of

resistor R7 and capacitor C6. Switch S2 is used for manual reset.


5. OPERATION

1. As the motor starts rotating, the laser light falls on the LDR when the slot aligns

with the laser beam and LDR.

2. Every time the motor completes one rotation, the mono-stable (NE555) triggers to

generate one pulse, which is indicated by LED1. So LED1 blinks at the rate of

motor speed.

3. As the first pulse arrives, it generates an interrupt for the microcontroller and

immediately the microcontroller starts counting the pulses. This is indicated by

LED2. The LCD shows the message "Counting RPM.

4. The microcontroller counts the pulses for a period of one second. Thereafter,

LED2 shows the message "Counting finished....." and goes off. The

microcontroller stores the count and multiplies it by 60 to give the final RPM

count.

5. The count is in hex format, so you have to convert it into decimal first. As the

LCD accepts only ASCII values, the decimal values are converted into ASCII and

shown on the LCD one by one.

6. Now if you press RST switch, the process repeats.


Figure 4 Continuity Testing

Figure 3 Breadboard Testing


6. SOFTWARE

The software for the RPM counter is written in 'C'

language and compiled using Keil Vision3 compiler.

The generated 'hex' file is burn into the microcontroller

using a suitable programmer.

The various functions are detailed below:

1. Main function initializes the timer, LCD, ports, etc. displays the message "RPM

counter", clears the timer content and enables the external interrupt. It remains in

the loop till 'rpm flag' (flag) is not set. When the RPM counting completes, it

displays the RPM value if it is within the range.

2. Int1 is an interrupt based function that is called automatically when there is a

negative edge on external interrupt 1 pin (P3.3). As soon as the first negative edge

arrives, the counter starts counting the external pulses for one second. After one

second, the content of TL0 is compared with A6h (166d). For any number greater

than 166, multiplication with 60 will yield a number that is longer than four digits,

which is out of the display range. This means RPM of max. 9960 (166x60) can be

displayed. Otherwise, the LCD will show the message "RPM Out of Range".

Figure 5 Connections on PCB


3. Display function performs three tasks one by one :

(i) Converts hex number in TL0 into decimal and multiplies it by 60

(ii) Converts the final decimal number into equivalent ASCII characters one

by one

(iii) Displays all the ASCII characters one by one on the LCD.

4. Write cmd function sends command byte to the LCD. It takes one argument byte

and sends sit to P1.

5. Write data function sends the data byte to be displayed on the LCD. It also takes

one argument byte and sends it to port P1.

6. Write str function writes the entire string (message) on the LCD. It takes the

pointer as an argument that points the address of the first character of the string.

Then through the pointer, it sends all the characters one by one to P1.

7. Busy function checks the status of the busy flag of the LCD. if the flag is set, that

means the LCD is not ready and the program remains within the loop. When the

flag is reset, the LCD is ready and the program comes out of the loop.

8. Delay function generates a fixed delay of one second using timer 0. The basic

delay is of 50 milliseconds, which is rotated in the loop for 20 times to generate

total delay of 20x50 ms = 1000 ms = 1 second.

6.1. PCB Designing & CAD

Although the circuit is tested on general purpose PCB but due to the

complexity of the connections make it very difficult to understand. So that

with the help of CAD it is done for much simple & easier.

In this project double side printed PCB is used means that printing is done on

both side of the PCB.


7. Program of RPM Counter

#include<reg51.h>

#include<string.h>

sbit rs = P3^5; // rs pin of LCD

sbit en = P3^2; // en pin of LCD

sbit rw = P3^7; // rw pin of LCD

sbit b = P1^7; // busy flag

sbit led = P3^0; // led indication

unsigned int flag=0; // rpm flag

void delay() // 1 sec delay

{

int k;

TL1 = 0xAF; // load value 15535=3CAF

TH1 = 0x3C;

TR1 = 1;

for(k=0;k<20;k++)

{

while(TF1==0);

TF1 = 0;

TL1 = 0xAF;

TH1 = 0x3C;

}

TR1 = 0;

}

void busy() // check busy flag

{

en = 0;

P1 = 0xFF;

rs = 0;

rw = 1;

while(b==1)

{

en=0;

en=1;

}

en=0;

}

void writecmd(unsigned char a) // send command byte to LCD

{

busy();

rs = 0;

rw = 0;


P1 = a;

en = 1;

en = 0;

}

void writedata(unsigned char b) // send data byte to LCD

{

busy();

rs = 1;

rw = 0;

P1 = b;

en = 1;

en = 0;

}

void writestr(unsigned char *s) // write string / message to LCD

{

unsigned char l,i;

l = strlen(s);

for(i=0;i<l;i++)

{

writedata(*s);

s++;

}

}

void int1(void) interrupt 2 // external interrupt 1 function

{

EA=0; // first disable interrupts

led=0; // give indication

writecmd(0x01);

writestr("counting RPM...."); // display message

TR0=1; // start timer 0

delay(); // give 1 sec delay

TR0=0; // stop timer

writecmd(0x80);

writestr("counting finish "); // display message

led=1;

if(TL0>0xA6)

{ // if value more then

166

writecmd(0xC0);

writestr("RPM out of range");// send message

}

else flag=1; // if not then set the

flag

}

void display() // convert hex to desimal and

{ // decimal to ascii


unsigned int tmp1,tmp2,t,t1,i,j;

unsigned char asci[4];

tmp1 = (TL0 & 0x0F); // get lower nibble of

TL0

tmp2 = TL0 >> 4; // get upper nibble of

TL0

tmp2 = tmp2*16; // multiply upper

nibble with 16

t = tmp1+tmp2; // get decimal number

t=t*60; // multiply it with

60

i=3;

if(t>=1000) // if more then 4

digits

{

while(t>10)

{

t1=t%10;

asci[i]=t1+0x30; // convert them one by one

t=t/10; // into ASCII

i--;

}

asci[0]=t+0x30;

}

else // otherwise convert

{

while(t>10)

{

t1=t%10;

asci[i]=t1+0x30; // last three digits

t=t/10;

i--;

}

asci[1]=t+0x30;

asci[0]=0x30; // and put first digit as 0

}

writecmd(0xC0);

writestr("currentRPM:"); // display current RPM and

for(j=0;j<4;j++)

writedata(asci[j]); // all four digits one by one

}

void main()

{

TMOD=0x15; // timer 0 in 16 bit counter

and timer 1 in 16 bit counter

P1 = 0x00; // P1 as output port


rs=0; // clear all LCD control

pins

en=0;

rw=0;

writecmd(0x3C); // initialize LCD

writecmd(0x0E);

writecmd(0x82);

writestr("RPM Counter"); // initially display message

TH0=0x00; // clear T0

TL0=0x00;

IE=0x84; // enable external interrupt

1

while(flag==0); // remain within loop till rpm flag is clear

display(); // when flag is set display current RPM value

while(1); // continuous loop

}

8. SOFTWARE USED FOR CRICUIT

i) For Schematic circuit design

Dip trace Schematic

ii) Circuit Testing

Circuit Wizard

iii) For PCB design

Dip trace PCB design


9. PCB LAYOUTS

Top Current Mirror


Bottom Current Mirror


Top Current Contrast


10. REFERENCES

1. RPM Counter definition: McGraw-Hill Science &

Technology Encyclopaedia

2. Revolution Per Minute:

http://en.wikipedia.org/wiki/Revolutions_per_minute

3. AT89C4051 Datasheet

http://www.atmel.com/dyn/resources/prod_documents/doc1001.pdf

4. NE555 Timer IC

http://www.datasheetcatalog.org/datasheet/philips/NE_SA_SE555_C_2.pdf

5. Resistance Colour Coding: http://www.vishay.com/docs/28733/28733.pdf

Rpm Counter Using Micro Controller

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