1. FREQUENCY COUNTER USING Silicon Labs C8051F020 microcontroller
Embedded Systems EGRE631
Smitha Gautham
Dept. of Electrical and Computer Engineering
Virginia Commonwealth University

2. Outline Application Theory Implementation Results and Discussions
Summary and Future Work

3. Examples of Application
Calibrate other equipment
Guitar tuner (attach to a crystal)
Measure rpm of wheel

4. Theory: Keeping track of time
System clock is 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

5. Theory: counting frequency
Every second: stop counter
Store value in counter register
Counter registers:16 bits → count 65,535
Higher frequencies: track counter overflows

6. Theory: LCD display
Display the frequency on LCD
Integer → string
Pass string to LCD routine

7. Implementation: Overview of Microcontroller
T4 is P0.4
Data port
Command port
Reference: Embedded programming , Chew Moi Tin and Gourab Sen Gupta

8. Implementation: Hardware Schematic

9. Implementation: Actual Hardware Set-up
Complete Set-up
MC and LCD

10. 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 }

11. Implementation: Crossbars
XBR0=0x04
XBR1=0x40
XBR2=0x58

12. 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; }

13. Implementation: Initializing Timer and Counter
CKCON=0x20
T2C0N=0X00

14. Implementation: Initializing Timer and Counter
T4CON=0X03

15. 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 }

16. 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);

17. 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

18. Implementation: Main Program cont’d{
zcnt=0;
if ( z> ) // if value in z is >550K indicate
ptra=& arr4[0];
ptra="out of range";
z=0;
if(ptra!='\0')
lcd_disp(* ptra);
lcd_init(); }

19. 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); }

20. Implementation: LCD Display
void lcd_init() {
cmd_write(0x38);
micro100_delay(30); // gives delay of 1 ms
cmd_write(0x0E); // Display on Cursor off; DCB
micro_delay(1);
cmd_write(0x01); //Clear the display
cmd_write(0x06); //Entry mode I/D S }

21. 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; }

22. 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; }

23. Range of few Hz to 100s of k HZ
Results
Range of few Hz to 100s of k HZ

24. 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

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

26. 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

27. Future Work Expand range of frequency counter
Other ways of implementations
Explore use of other Timers/Counters

28. Thank you Questions?