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

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 XBR0=0x04 XBR1=0x40 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

Implementation: Initializing Timer and Counter T4CON=0X03

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 cmd_write(0x06); //Entry mode 0000 01 I/D S }

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; }

Range of few Hz to 100s of k HZ 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 you Questions?