FREQUENCY COUNTER USING

Silicon Labs C8051F020 microcontroller

Embedded Systems EGRE631

Smitha Gautham

Dept. of Electrical and Computer Engineering

Virginia Commonwealth University

Outline

• Application

• Theory

• Implementation

• Results and Discussions

• Summary and Future Work

Examples of Application

• Calibrate other equipment

• Guitar tuner (attach to a crystal)

• Measure rpm of wheel

Theory: Keeping track of time

• System clock is 22.45 MHz.

• Timer count = 22,450 → 1 ms

• Start counter

• Counter counts external clock pulses

• Every 1 ms → interrupt

• Count 1000 in ISR → 1 second delay

Theory: counting frequency

• Every second: stop counter

• Store value in counter register

• Counter registers:16 bits → count 65,535

• Higher frequencies: track counter overflows

Theory: LCD display

• Display the frequency on LCD

• Integer → string

• Pass string to LCD routine

Implementation: Overview of Microcontroller

Reference: Embedded programming , Chew Moi Tin and Gourab Sen Gupta

T4 is P0.4

Data port

Command port

Implementation: Hardware Schematic

Implementation: Actual Hardware Set-up

Complete Set-up MC and LCD

Implementation: Initializing cross-bars

• Timer 2 to count internal clock pulses

• Counter 4 to count external frequency

• Configuring the Crossbar registers

void init_crossbar (void)

{

XBR0 = 0x04; // UART 0 TX to P0.0, RX to P0.1

XBR1 = 0x40; // Sysclk out

XBR2 = 0x58; // Enable cross bar rout T4 to port pin

}

Implementation: Crossbars

XBR1=0x40

XBR0=0x04

XBR2=0x58

Implementation: Initializing Ports

• Configuring ports void init_ports(void)

{

P0MDOUT = 0x00; //configure P0 as input port

P0=0x04;

P1MDOUT = 0xFF; // P1 is push pull

P2MDOUT = 0xFF;// P2 as push pull

P3MDOUT = 0x00;

P5 = 0x00;

}

Implementation: Initializing Timer and Counter

CKCON=0x20

T2C0N=0X00

T4CON=0X03

Implementation: Initializing Timer and Counter

Implementation: Initialize timer

void init_timer(int cnt) { T2CON =0x00; //clear Timer 2 T4CON=0x03; //clear Timer4 config Timer 4 as counter CKCON= 0X20; //Timer 2 uses sys clk

TMR2RL=-cnt; //load count to get 1 ms delay TMR2=TMR2RL; TMR4RL=0x00; // clear Counter4 TMR4=TMR4RL; ET2=1; //Enable Timer2 interrupt TR2=1; // Run Timer2 T4CON= 0x0F;//Run Counter4 }

Implementation: ISR

void Timer2_ISR (void) interrupt 5 { unsigned int scnt;

TF2=0; //clear timer2 interrupt flag scnt++;

if (scnt==100) // ISR every 1ms, 1ms *100 gives .1 s { flag=1;

z=z+TMR4; //TMR4 value is repeatedly added to z TMR4=0x00; scnt=0; zcnt=zcnt+1; // to get 10 counts of .1 s

} if (zcnt==10) //.1s* 10 gives 1 s delay

{ T4CON =0x00; init_timer(mSEC_CNT);

}}

Implementation: Main Program

int main(void)

{

unsigned int arr4[12];

unsigned int *ptra;

Init();

EA=1;

init_timer(mSEC_CNT);

while(1)

{

if(flag==1)

{

flag=0;

if(zcnt==10)

// Initialize the microcontroller

// Enable Global Interrupts

// Initialize timer

//flag is enabled after .1s

// zcnt = 10 means 1 s is complete

Implementation: Main Program cont’d

{ zcnt=0; if ( z> 550000 ) // if value in z is >550K indicate { ptra=& arr4[0]; ptra="out of range";

z=0;if(ptra!='\0') lcd_disp(* ptra); lcd_init();

}

Implementation: Main Program cont’d

else sprintf(arr4, "%ld Hz", z); // convert z to string and display z=0; ptra= & arr4[0];

lcd_init(); lcd_disp(*ptra);

} }

}

}

Implementation: LCD Display

void lcd_init()

{ cmd_write(0x38); micro100_delay(30); // gives delay of 1 ms cmd_write(0x0E); // Display on Cursor off; 0000 1DCB micro_delay(1); cmd_write(0x01); //Clear the display micro_delay(1); cmd_write(0x06); //Entry mode 0000 01 I/D S micro_delay(1);

}

Implementation: LCD Display cont’d

void cmd_write(char cmd) { RS=0; micro_delay(1); RW=0; micro100_delay(10); // gives delay of 1 ms LCD_DAT_PORT = cmd; E=1; micro_delay(1); //gives a delay of 1 micro second E=0; }

Implementation: LCD Display cont’d

void data_write(char dat)

{

EA=1;

RS=1;

micro_delay(1);

RW=0;

micro100_delay(10);

LCD_DAT_PORT = dat; //Data is written

E=1;

micro_delay(1); //enable must be high for 300 ns to capture data

E=0;

}

Results

Range of few Hz to 100s of k HZ

Discussions

• Sampling time = 0.1 s• Number of times = 10• Total =1 s

• Register TMR4→ MAX 65,535 every 0.1 s• Z=z+TMR4 each time• Max Freq= 655,350 Hz

Discussions

• Theoretically cannot measure freq > 655,350 Hz• Display “0” beyond 550,000 Hz

Summary

• Inexpensive frequency counter implemented

• Can measure frequency from 1 Hz to 550 K Hz

• TMR4 is16 bits → max count of 65,535

• repeat 10 times per sec→ max frequency of 655,350

Future Work

• Expand range of frequency counter

• Other ways of implementations

•Explore use of other Timers/Counters

Thank youQuestions?