Frequency meter based on STC8 microcontroller

Frequency measurement principle: frequency is measured by counting method.

Implementation method: Using the feature of 51 MCU timer as external pulse counter, frequency counting can be realized. Specifically, two timers are used. In this example, timer 0 is used as external pulse counter to capture external pulse (falling edge trigger), and timer 3 generates 1s timing to extract counting frequency.

code show as below

//System clock frequency 24MHz

#include "STC8.H"

bit send_flag = 0;

unsigned int freq = 0; //frequency count

unsigned long cont_freq = 0; //Frequency count overflow

unsigned char res[6]; //Frequency conversion result

void TM0_Init();

void TM3_Init();

void UartSend(unsigned char dat);

void UartInit(void);

void UartSendStr(unsigned char *p);

void Num_Cut(unsigned long num);

void Uart_Send_Str(unsigned char str[],unsigned char len,bit mode);

void main ()

{

TM0_Heat();    

TM3_Init();    

UartInit();    

while(1)

{ 

    if(send_flag)

{

        Num_Cut(cont_freq+(unsigned long)freq); //Frequency value equals overflow value plus current value

  send_flag = 0;

  UartSendStr("Freq: ");

Uart_Send_Str(res,6,1);

Uart_Send_Str(res,6,0);

UartSendStr(" Hzn");

}

}

} 

/******************************************************************************

 * Description: Timer 3 initialization function, timing time 1ms

 * Parameters: None

 * Return value: None

 ******************************************************************************/

void TM3_Init()

{

T3L = 0x35; //Set the initial timing value, 1ms

  T3H = 0xA2; //Set the initial timing value

    T4T3M |= 0x08; //Start the timer

  T4T3M |= 0x02;    //Timer clock 1T mode

    IE2 |= ET3; //Enable timer interrupt

    EA = 1; // Enable general interrupt

}

/******************************************************************************

 * Description: Timer 0 initialization function, external counting mode

 * Parameters: None

 * Return value: None

 ******************************************************************************/

void TM0_Init()

{

  TMOD |= 0x04; //Set external counting mode

  TMOD |= 0x01; //Working mode 1, 16-bit does not automatically reload

  TR0 = 1; //Open the counter

    TH0 = 0x00; //Counter reset

  TL0 = 0x00;                                

  ET0 = 1; //Open counter interrupt

}

/******************************************************************************

 * Description: Timer 0 interrupt service function 

 * Parameters: None

 * Return value: None

 ******************************************************************************/

void TM0_Isr() interrupt 1

{  

    cont_freq += 65536; // Overflow count, each overflow, the count times is TH0<<8|TL0 = 0xffff, after debugging, add 1

  TH0 = 0x00; //Reset counter

  TL0 = 0x00; //Reset counter

}

/******************************************************************************

 * Description: Timer 3 interrupt service function

 * Parameters: None

 * Return value: None

 ******************************************************************************/

void TM3_Isr() interrupt 19

{   

  static unsigned int ms_flag = 0; //1s count flag

if(ms_flag++ == 1000)

{

freq = (TH0<<8|TL0); //Get the current counter value          

ms_flag = 0; //1s count flag reset

send_flag = 1; //Serial port send flag is set

  TH0 = 0x00; //Reset counter

  TL0 = 0x00; //Reset counter

}

AUXINTIF &= ~T3IF; // Clear interrupt flag

}

/******************************************************************************

 * Description: Serial port 1 initialization function, baud rate 9600 

 * Parameters: None

 * Return value: None

 ******************************************************************************/

void UartInit(void) //9600bps@24.000MHz

{

SCON |= 0x50; //8-bit data, variable baud rate

AUXR |= 0x01; //Serial port 1 selects timer 2 as the baud rate generator

AUXR |= 0x04; //Timer 2 clock is Fosc, i.e. 1T

T2L = 0x8F; //Set the initial timing value

T2H = 0xFD; //Set the initial timing value

AUXR |= 0x10; //Start timer 2

}

/******************************************************************************

* Description: Serial port character sending and function 

* Input parameter: Send character

* Return value: None

******************************************************************************/

void UartSend(unsigned char dat)

{

    SBUF =that;     

    while(!IF);

  TI = 0;

}

/******************************************************************************

* Description: Serial port string sending function

* Input parameter: Send string

* Return value: None

******************************************************************************/

void UartSendStr(unsigned char *p)

{

    while (*p)

    {

        UartSend(*p++);

    }

}

 /******************************************************************************

 * Description: Number splitting function

 * Input parameter: Split number

 * Return value: None

 ******************************************************************************/

void Num_Cut(unsigned long num)

{ unsigned long temp = num; 

unsigned char cont = 5;

while(temp != 0)

{

res[cont--] = (unsigned char)(temp % 10);

temp /= 10;

}

  cont_freq = 0;

}

/******************************************************************************

* Description: Serial port digital array sending function

* Input parameters: str: array, len: array length or data length to be sent, mode: 1 to send, 0 to clear the array

* return value: 

******************************************************************************/

void Uart_Send_Str(unsigned char str[],unsigned char len,bit mode)

{

unsigned char k;

if(mode == 1)

{

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

{

UartSend(48 + str[k]);

}

}else

{

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

{

str[k] = 0;

}

}

}

The test results are analyzed as follows: