1. Design introduction

Currently, a heart rate detector is implemented based on STC89C52 microcontroller and PCF8591, PulseSensor heart rate sensor, SSD1306 OLED display and other components. The detector can collect the analog signal output by the heart rate sensor, calculate the real-time heart rate value after AD conversion, and then transmit the heart rate value to the OLED display for display through the IIC protocol. Users only need to fix the heart rate sensor on the body and start the heart rate detector to conveniently monitor their heart rate in real time.

This project has a wide range of applications and can be used in health management, fitness exercises, medical treatment and other fields. At home, people can use this heart rate monitor to monitor their own heart rate in a timely manner and effectively manage and control their health; in gyms or fitness coaching centers, coaches can use this heart rate monitor to monitor athletes' heart rate changes in order to target The training plan can be adjusted accordingly to improve the training effect; in medical institutions, medical staff can use the heart rate monitor to monitor the heart rate of patients, detect abnormalities in time, and provide a strong basis and reference for patient treatment.

2. Hardware selection

Hardware required for this project:

1. STC89C52 microcontroller: As the main control chip, it is responsible for reading the analog signal of the PulseSensor heart rate sensor, performing AD conversion, calculating the heart rate value, and transmitting the heart rate value to the OLED display for display through the IIC protocol.

2. PCF8591 module: used to implement the STC89C52 microcontroller to perform data acquisition and AD conversion on the PulseSensor heart rate sensor through the IIC bus.

3. PulseSensor heart rate sensor: used to collect the weak heartbeat signal of the human body and output the signal to the PCF8591 module.

4. SSD1306 OLED display: used to display heart rate detection results, including heart rate value and unit.

5. DuPont wire, breadboard: used to connect various hardware modules and build circuit prototypes.

3. Implement the code

The following is the core code of the project, which collects the heart rate through the PCF8591 connected to the PulseSensor heart rate sensor, and displays it on the 0.96-inch OLED display through the IIC protocol:

#include < reg52.h >

 #include < intrins.h >

 #define uchar unsigned char

 #define uint unsigned int

 sbit SCL = P1^0;

 sbit SDA = P1^1;

 sbit LED = P2^0;

 #define ADDR_PCF8591 0x90 // IIC address of PCF8591: 1001 0000

 #define CMD_PCF8591_WR 0x40 //PCF8591 write data command word: 0100 CCCC, CCCC is channel selection

 #define CMD_PCF8591_RD 0x41 // PCF8591 read data command word: 0100 CCCC, CCCC is channel selection

 #define ADDR_OLED 0x78 // IIC address of SSD1306 OLED display: 0111 1000

 uchar heartRate[3]; // String to store heart rate value

 /**

  * Delay function to control IIC communication speed

  */

 void Delay()

 {

     uint i, j;

     for(i=0; i< 50; i++)

         for(j=0; j< 500; j++);

 }

 /**

  *IIC start signal

  */

 void IIC_Start()

 {

     SCL = 1;

     SDA = 1;

     Delay();

     SDA = 0;

     Delay();

     SCL = 0;

 }

 /**

  *IIC stop signal

  */

 void IIC_Stop()

 {

     SCL = 0;

     SDA = 0;

     Delay();

     SCL = 1;

     SDA = 1;

     Delay();

 }

 /**

  *IIC sends one byte of data

  * @param byte sent byte

  * @return received response bit

  */

 volatile IIC_SendByte(volatile byte)

 {

     fly i, ack;

     for(i=0; i< 8; i++)

     {

         SDA = (bit)(byte & 0x80);

         byte < <= 1;

         Delay();

         SCL = 1;

         Delay();

         SCL = 0;

     }

     SDA = 1;

     Delay();

     SCL = 1;

     Delay();

     ack = SDA;

     SCL = 0;

     return ack;

 }

 /**

  * Initialize PCF8591 module

  */

 void Init_PCF8591()

 {

     IIC_Start();

     IIC_SendByte(ADDR_PCF8591);

     IIC_SendByte(CMD_PCF8591_WR | 0);

     IIC_Stop();

 }

 /**

  * Read the AD value of PCF8591

  * @param ch The selected channel number

  * @return the value after AD conversion

  */

 fly Read_PCF8591(fly ch)

 {

     volatile value;

     IIC_Start();

     IIC_SendByte(ADDR_PCF8591);

     IIC_SendByte(CMD_PCF8591_WR | ch);

     IIC_Stop();

     IIC_Start();

     IIC_SendByte(ADDR_PCF8591 | 0x01);

     value = IIC_SendByte(0xFF);

     IIC_Stop();

     return value;

 }

 /**

  * Initialize SSD1306 OLED display

  */

 void Init_OLED()

 {

     IIC_Start();

     IIC_SendByte(ADDR_OLED);

     IIC_SendByte(0xAE); //Close display

     IIC_SendByte(0x00); //Lower 4 bits of column address

     IIC_SendByte(0x10); //High 4 bits of column address

     IIC_SendByte(0x40); // Starting row address

     IIC_SendByte(0xB0); //Set page address

     IIC_SendByte(0x81); // Contrast setting command

     IIC_SendByte(0xCF); //Contrast value

     IIC_SendByte(0xA1); // Segment multiplexing settings

     IIC_SendByte(0xA6); //Normal display mode

     IIC_SendByte(0xA8); // Multiplexing settings

     IIC_SendByte(0x3F); //Number of pages-1

     IIC_SendByte(0xC8); //Scan mode setting

     IIC_SendByte(0xD3); //Set display offset

     IIC_SendByte(0x00);

     IIC_SendByte(0xD5); // Frequency setting command

     IIC_SendByte(0x80); // Frequency division coefficient

     IIC_SendByte(0xD9); //Set the precharge cycle

     IIC_SendByte(0xF1);

     IIC_SendByte(0xDA); //Set the COM hardware connection method

     IIC_SendByte(0x12);

     IIC_SendByte(0xDB); // VCOMH setting

     IIC_SendByte(0x40);

     IIC_SendByte(0xA4); // All lit/normal display

     IIC_SendByte(0xA6); //Normal/reverse display control

     IIC_SendByte(0xAF); // Turn on display

     IIC_Stop();

 }

 /**

  * Display string on OLED

  * @param x start column address

  * @param y start page address

  * @param str The string to be displayed

  */

 void ShowString_OLED(float x, float y, float *str)

 {

     fly i = 0;

     IIC_Start();

     IIC_SendByte(ADDR_OLED);

     IIC_SendByte(0x00); //Lower 4 bits of column address

     IIC_SendByte(0x10); //High 4 bits of column address

     IIC_SendByte(0xB0 + y);//Set page address

     for(i=0; str[i]!='\0'; i++)

     {

         IIC_SendByte(0xB0 + y);

         IIC_SendByte((x + 8*i) & 0x0F);

         IIC_SendByte(((x + 8*i) > > 4) | 0x10);

         IIC_SendByte(str[i]);

     }

     IIC_Stop();

 }

 /**

  * Main function, heart rate calculation and display

  */

 void main()

 {

     Init_PCF8591(); // Initialize PCF8591 module

     Init_OLED(); // Initialize OLED display

     while(1)

     {

         uchar adValue = Read_PCF8591(0); // Read the AD value of PCF8591

         uint timeInterval = 100; //Set the time interval for collecting heart rate, in milliseconds

         uint count = 0; // Counter that counts the number of pulse beats

         uint heartRateValue = 0; // Calculated heart rate value

         for (uint i=0; i< timeInterval; i++) // Collect data within a certain period of time

         {

             if (adValue > 200) // When the AD value is higher than the threshold, count the number of pulse beats

             {

                 count++;

                 while(adValue > 100) // Wait for a period of time to avoid the same pulse being counted repeatedly

                 {

                     adValue = Read_PCF8591(0);

                 }

             }

             adValue = Read_PCF8591(0); // Read the next AD value

         }

         heartRateValue = (uint)(count * 60.0 / timeInterval); // Calculate heart rate value

         sprintf(heartRate, "%d", heartRateValue); // Convert heart rate value to string

         ShowString_OLED(0, 0, "Heart Rate:"); // Display title on OLED

         ShowString_OLED(80, 0, heartRate); // Display heart rate value on OLED

         ShowString_OLED(96, 0, "bpm"); // Display units on OLED

     }

 }