DS18B20 Experiment of digital temperature sensor

STM32 Although there is a temperature sensor inside , But because of the chip temperature rise and other problems , It is quite different from the actual temperature , therefore , In this chapter, we will show you how to pass the STM32
To read the temperature of the external digital temperature sensor , To get a more accurate ambient temperature . In this chapter , We will learn to use single bus technology , Through it STM32 And external temperature sensor (
DS18B20) Communication of , The temperature obtained from the temperature sensor is displayed in the TFTLCD On the module .

1 DS18B20 brief introduction
DS18B20 By DALLAS
A new product launched by semiconductor company “ One wire bus ” Temperature sensor of interface . Compared with the traditional thermistor and other temperature measuring elements , It is a new type of small size , Wide voltage range , Digital temperature sensor with simple interface with microprocessor . One wire bus structure is simple and economical , It makes it easy for users to set up sensor networks , So as to introduce a new concept for the construction of measurement system , The measuring temperature range is -55~+125℃
, The accuracy is ±0.5℃. The field temperature is directly controlled by “ One wire bus ” Digital mode of transmission , The anti-interference performance of the system is greatly improved . It can read the temperature directly , And it can be realized by simple programming according to the actual requirements 9~l2
Digital value reading mode of bit . It works in 3~5.5V Voltage range , Various packaging forms are adopted , So the system design is flexible , convenient , The set resolution and the alarm temperature set by the user are stored in the EEPROM
in , Keep it after power down .

ROM In 64 Bit serial number is recorded by light before leaving factory , It can be seen as the DS18B20 Address sequence code of , each DS18B20 Of 64 The bit serial numbers are not the same . 64 position
ROM What's the arrangement : front 8 Bit is the product family code , next 48 The position is DS18B20 Serial number of , last 8 One is in the front 56
Bit cyclic redundancy check code (CRC=X8+X5+X4+1). ROM The role is to make every DS18B20 It's all different , In this way, it is possible to connect multiple nodes on one bus DS18B20.
All single bus devices require strict signal timing , To ensure the integrity of the data . DS18B20 share 6 Two signal types : Reset pulse , Reply pulse , write 0, write 1, read 0 And read
1. All these signals , Except for the reply pulse , The synchronous signal is sent by the host . And send all the commands and data are the first byte . Here we briefly introduce the timing of these signals :

①, Unique single bus interface mode ,DS18B20 Only one port line is needed to connect with microprocessor Modern microprocessors and DS18B20 Two way communication based on Internet . The anti-interference performance of the system is greatly improved .

② , Measuring range -55℃~+125℃, The accuracy is ±0.5℃.

③, Support multipoint networking , Multiple DS18B20 It can be connected in parallel on the only three wires , Parallel connection at most 8 individual , Multi point temperature measurement , If the quantity is too much , The power supply voltage will be too low , So the signal transmission is unstable .

④, Working power supply : 3.0~5.5V/DC ( Data line parasitic power supply can be used ).

⑤ , No peripheral components are needed in use .

⑥, The measurement results are as follows 9~12 Serial transmission in bit word mode .

1) Reset pulse and reply pulse
All communication on a single bus starts with an initialization sequence . Host output low level , Keep low for at least 480us,, To generate a reset pulse . Then the host releases the bus , 4.7K
The pull-up resistance will pull the single bus high , delayed 15~60 us, And enter the receiving mode (Rx). next DS18B20 Pull down the bus 60~240
us, To generate a low level reply pulse , In case of low level , Further delay 480 us.
2) Write timing
Write timing includes write timing 0 Timing and writing 1 sequential . All write timing requires at least 60us, And in 2 At least two independent write sequences are required 1us
Recovery time for , Both write sequences start when the host pulls down the bus . write 1 sequential : Host output low level , delayed 2us, Then release the bus , delayed 60us. write 0 sequential : Host output low level , delayed
60us, Then release the bus , delayed 2us.
3) Reading sequence
The single bus device is only used when the host sends the read sequence , To transmit data to the host , therefore , After the host sends the read data command , Read sequence must be generated immediately , So that the slave can transfer data . All read sequences require at least
60us, And in 2 At least two independent read sequences are required 1us Recovery time for . Each read sequence is initiated by the host , At least pull down the bus
1us. The host must release the bus during read timing , And at the beginning of the sequence 15us Internal sampling bus status . The typical reading sequence process is :
Host output low level delay 2us, Then the host goes into input mode 12us, Then read the current level of the single bus , Then delay 50us.
After understanding the single bus timing , Let's see DS18B20 Typical temperature reading process , DS18B20 The typical temperature reading process is : reset  hair SKIP ROM command (
0XCC)  Send the start conversion command ( 0X44) delayed  reset  send out SKIP ROM command ( 0XCC)  Send read memory command ( 0XBE)
 Read two bytes of data continuously ( That is temperature ) end .
DS18B20 encapsulation

2. Connection mode

Connect to STM32 upper Pin interface of ( Other options are available ) The connected pins are used for later programming

Single bus is a half duplex communication mode

DS18B20 share 6 Two signal types : Reset pulse , Reply pulse , write 0, write 1, read 0 And read 1. All these signals , Except for the reply pulse , The synchronous signal is sent by the host . And send all the commands and data are the first byte .

Talking about signal types , Talking about the way of code configuration , Let us know STM32 drive 18B20 process .

  The signal line :PG9

//IO Direction setting

#define DS18B20_IO_IN()  {GPIOG->MODER&=~(3<<(9*2));GPIOG->MODER|=0<<9*2;}  
 //PG9 Input module

#define DS18B20_IO_OUT() {GPIOG->MODER&=~(3<<(9*2));GPIOG->MODER|=1<<9*2;}   
 //PG9 Output mode

IO operation                           

#define    DS18B20_DQ_OUT PGout(9) // Data port PG9

#define    DS18B20_DQ_IN  PGin(9)  // Data port     PG9 

( 1).  Reset pulse

All communication on a single bus starts with an initialization sequence . Host output low level , Keep low for at least 480
us,, To generate a reset pulse . Then the host releases the bus ,4.7K The pull-up resistance will pull the single bus high , delayed 15~60 us, And enter the receiving mode (Rx). next DS18B20 Pull down the bus 60~240
us, To generate a low level reply pulse .

// reset DS18B20 void DS18B20_Rst(void)      

{                    

DS18B20_IO_OUT(); // Set to output mode    

DS18B20_DQ_OUT=0; // Pull down DQ    

delay_us(750);    // Pull down 750us( at least 480us)    

DS18B20_DQ_OUT=1; //DQ=1 Pull up release bus    

delay_us(15);     //15US    

// Enter acceptance mode , Waiting for response signal .

}

② Response signal

// wait for DS18B20 My response

// return 1: Not detected DS18B20 The existence of     return 0: existence

u8 DS18B20_Check(void)       

{      

u8 retry=0;    

DS18B20_IO_IN();//SET PA0 INPUT        

while (DS18B20_DQ_IN&&retry<200)    

{            

retry++;          

 delay_us(1);    

 };        

if(retry>=200)return 1;    

else retry=0;    

while (!DS18B20_DQ_IN&&retry<240)    

{            

retry++;            

delay_us(1);    

};    

if(retry>=240)return 1;            

return 0;

}

③ Write timing

Write timing includes write timing 0 Timing and writing 1 sequential . All write timing requires at least 60us, And in 2 At least two independent write sequences are required 1us Recovery time for , Both write sequences start when the host pulls down the bus .
write 1 sequential : Host output low level , delayed 2us, Then release the bus , delayed 60us. write 0 sequential : Host output low level , delayed 60us, Then release the bus , delayed 2us.

/ Write a byte to DS18B20 //dat: Bytes to write

void DS18B20_Write_Byte(u8 dat)    

 {                

u8 j;

 u8 testb;    

DS18B20_IO_OUT();// set up PA0 For output    

for (j=1;j<=8;j++)    

{        

testb=dat&0x01;        

dat=dat>>1;        

if (testb) // High output      

  {          

  DS18B20_DQ_OUT=0;// Host output low level            

delay_us(2);                  // delayed 2us            

DS18B20_DQ_OUT=1;// Release the bus            

delay_us(60); // delayed 60us                    

}        

else // Low output        

{            

DS18B20_DQ_OUT=0;// Host output low level            

delay_us(60);               // delayed 60us            

DS18B20_DQ_OUT=1;// Release the bus            

delay_us(2);                  // delayed 2us              

  }    

}

}

④ Reading sequence

The single bus device is only used when the host sends the read sequence , To transmit data to the host , therefore , After the host sends the read data command , Read sequence must be generated immediately , So that the slave can transfer data .
All read sequences require at least 60us, And in 2 At least two independent read sequences are required 1us Recovery time for . Each read sequence is initiated by the host , At least pull down the bus 1us. The host must release the bus during read timing , And at the beginning of the sequence 15us Internal sampling bus status .

The typical reading sequence process is : Host output low level delay 2us, Then the host goes into input mode 12us, Then read the current level of the single bus , Then delay 50us.

The typical reading sequence process is : Host output low level delay 2us, Then the host goes into input mode 12us, Then read the current level of the single bus , Then delay 50us.

// from DS18B20 Read a bit // Return value :1/0

u8 DS18B20_Read_Bit(void)              // read one bit

{

    u8 data;    

DS18B20_IO_OUT();// Set to output    

DS18B20_DQ_OUT=0; // Output low level 2us    

delay_us(2);    

DS18B20_DQ_OUT=1; // Pull up release bus    

DS18B20_IO_IN();// Set to input    

delay_us(12);// delayed 12us  

 if(DS18B20_DQ_IN)data=1;// Read bus data    

else data=0;        

delay_us(50);  // delayed 50us            

return data;

}

Read a byte of data

// from DS18B20 Read a byte // Return value : Data read

u8 DS18B20_Read_Byte(void)    // read one byte

{            

u8 i,j,dat;    

dat=0;  

 for (i=1;i<=8;i++)  

 {        

j=DS18B20_Read_Bit();        

dat=(j<<7)|(dat>>1);    

}                                

return dat;

}

Let's see DS18B20 Typical temperature reading process ,DS18B20 The typical temperature reading process is : reset  hair SKIP
ROM command (0XCC) Send the start conversion command (0X44) delayed  reset  send out SKIP
ROM command (0XCC) Send read memory command (0XBE) Read two bytes of data continuously ( That is temperature ) end .

3 Finally, the final source program ( You need to put the program in the STM32F4 Library function programming )

Open our DS18B20 Digital temperature sensor experiment project can see that we added ds18b20.c Documents and their
Header file ds18b20.h file , All ds18b20 Driver code and related definitions are distributed in these two files .
//ds18b20.c code

// reset DS18B20

#include "DS18B20"
void DS18B20_Rst(void)
{
DS18B20_IO_OUT(); //SET PG11 OUTPUT
DS18B20_DQ_OUT=0; // Pull down DQ
delay_us(750); // Pull down 750us
DS18B20_DQ_OUT=1; //DQ=1
delay_us(15); //15US
}
// wait for DS18B20 My response
// return 1: Not detected DS18B20 The existence of
// return 0: existence
u8 DS18B20_Check(void)
{
u8 retry=0;
DS18B20_IO_IN();//SET PG11 INPUT
while (DS18B20_DQ_IN&&retry<200) { retry++; delay_us(1); };
if(retry>=200)return 1;
else retry=0;
while (!DS18B20_DQ_IN&&retry<240) {retry++; delay_us(1); };
if(retry>=240)return 1;
return 0;
}
// from DS18B20 Read a bit
// Return value : 1/0
u8 DS18B20_Read_Bit(void)
{
u8 data;
DS18B20_IO_OUT();//SET PG11 OUTPUT
DS18B20_DQ_OUT=0;
delay_us(2);
DS18B20_DQ_OUT=1;
DS18B20_IO_IN();//SET PG11 INPUT
delay_us(12);
if(DS18B20_DQ_IN)data=1;
else data=0;
delay_us(50);
return data;
}
// from DS18B20 Read a byte
// Return value : Data read
u8 DS18B20_Read_Byte(void)
{
u8 i,j,dat;
dat=0;
for (i=1;i<=8;i++)
{
j=DS18B20_Read_Bit();
dat=(j<<7)|(dat>>1);
}
return dat;
}
// Write a byte to DS18B20
//dat: Bytes to write
void DS18B20_Write_Byte(u8 dat)
{
u8 j;
u8 testb;
DS18B20_IO_OUT();//SET PG11 OUTPUT;
for (j=1;j<=8;j++)
{
testb=dat&0x01;
dat=dat>>1;
if (testb)
{
DS18B20_DQ_OUT=0;// Write 1
delay_us(2);
DS18B20_DQ_OUT=1;
delay_us(60);
}
else
{
DS18B20_DQ_OUT=0;// Write 0
delay_us(60);
DS18B20_DQ_OUT=1;
delay_us(2);
}
}
}
// Start temperature conversion
void DS18B20_Start(void)
{
DS18B20_Rst();
DS18B20_Check();
DS18B20_Write_Byte(0xcc);// skip rom
DS18B20_Write_Byte(0x44);// convert
}
// initialization DS18B20 Of IO mouth DQ Simultaneous detection DS The existence of
// return 1: non-existent
// return 0: existence
u8 DS18B20_Init(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOG, ENABLE);// Enable GPIOG Clock
//GPIOG9

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;// Normal output mode
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;// Push pull output
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;//50MHz
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;// Pull up
GPIO_Init(GPIOG, &GPIO_InitStructure);// initialization
DS18B20_Rst();
return DS18B20_Check();
}

// from ds18b20 Get the temperature value
// accuracy : 0.1C
// Return value : Temperature value ( -550~1250)
short DS18B20_Get_Temp(void)
{
u8 temp;
u8 TL,TH;
short tem;
DS18B20_Start();// ds1820 start convert
DS18B20_Rst();
DS18B20_Check();
DS18B20_Write_Byte(0xcc);// skip rom
DS18B20_Write_Byte(0xbe);// convert
TL=DS18B20_Read_Byte(); // LSB
TH=DS18B20_Read_Byte(); // MSB
if(TH>7)
{
TH=~TH;
TL=~TL;
temp=0; // The temperature is negative
}else temp=1; // The temperature is positive
tem=TH; // Get the top eight
tem<<=8;
tem+=TL; // Get the bottom eight
tem=(double)tem*0.625;// transformation
if(temp)return tem; // Return temperature value
else return -tem;
}
This part of the code is read according to the single bus operation sequence we introduced earlier DS18B20 The temperature value of ,DS18B20
The temperature of DS18B20_Get_Temp Function read , The return value of this function is signed short integer data , Of the return value
The scope is -550~1250, In fact, the temperature value has expanded 10 times .
Principal function ds18b20.h

#include "sys.h"
#include "delay.h"
#include "usart.h"
#include "led.h"
#include "lcd.h"
#include "ds18b20.h"

int main(void)
{
u8 t=0;
short temperature;
NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);// Setting system interrupt priority group 2
delay_init(168); // Initialize delay function
uart_init(115200); // Initialize serial port baud rate to 115200
LED_Init(); // initialization LED
LCD_Init();
POINT_COLOR=RED;// Set the font to red
LCD_ShowString(30,50,200,16,16,"ALIX");
LCD_ShowString(30,70,200,16,16,"DS18B20 TEST");
LCD_ShowString(30,90,200,16,16,"ALIX");
LCD_ShowString(30,110,200,16,16,"2018/7/22");
while(DS18B20_Init()) //DS18B20 initialization
{
LCD_ShowString(30,130,200,16,16,"DS18B20 Error");
delay_ms(200);
LCD_Fill(30,130,239,130+16,WHITE);
delay_ms(200);
}
LCD_ShowString(30,130,200,16,16,"DS18B20 OK");
POINT_COLOR=BLUE;// Set the font to blue
LCD_ShowString(30,150,200,16,16,"Temp:    . C");
while(1)
{
if(t%10==0)// each 100ms Read once
{
temperature=DS18B20_Get_Temp();
if(temperature<0)
{
LCD_ShowChar(30+40,150,'-',16,0); // Show minus sign
temperature=-temperature; // Turn to positive
}else LCD_ShowChar(30+40,150,' ',16,0); // Remove the minus sign
LCD_ShowNum(30+40+8,150,temperature/10,2,16); // Show positive part
LCD_ShowNum(30+40+32,150,temperature%10,1,16); // Show decimal part
}
delay_ms(10); t++;
if(t==20)
{
t=0; LED0=!LED0;
}
}

 

 

 

 

 

 

 

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