1.MLX90614简介
MLX90614是一种低性价比的非接触式温度传感器，主要用于不能直接接触测量温度的场合。常用型号是MLX90614-XYZ，其中X代表其供电电压，可选A-5V供电、B-3.3V供电、D-3.3V供电(医疗)；Y可选代表热电堆数量A-单感应区，B-双感应区，C-温度梯度补偿； Z代表包装类型，可选A-90度标准封装视角，C-35度视角、F-10度视角。视角越小，可测距离越远。我们更关心的是它与单片机的通信，MLX90614有四个引脚，其中VCC与GND是电源引脚，SCL和SDA是SMBUS通信引脚。有关SMBUS可参考通信协议SMBUS通信协议。
2.MLX90614硬件连接
显然，普通人只能买BAA型号的MLX90614来玩，传感器视角大，测量距离要求高，一般低于1cm会比较准确。在这里使用。MLX90614模块，具体硬件连接图如下(未找到)BAA模块图，用BCC替换，模块引脚是一样的): 
3.软件实现
实现软件只需按协议编写，网上参考资料也比较多，MLX90614驱动文件由.c和.h这里使用的通信共同完成I/O为单片机的PB15 PB引脚的主要内容如下： mlx90614.c
/********************************************************************************************************** author: 芯晟科电子&offical date : 2020/05/10 address: copyright : 2020-2030 **********************************************************************************************************/ #include "mlx90614.h" #define ACK 0 #define NACK 1 #define SA 0x00 #define RAM_ACCESS 0x00 #define EEPROM_ACCESS 0x20 #define RAM_TOBJ1 0x07 #define SMBUS_PORT GPIOB #define SMBUS_SCK GPIO_Pin_15 #define SMBUS_SDA GPIO_Pin_14 #define RCC_APB2Periph_SMBUS_PORT RCC_APB2Periph_GPIOB #define SMBUS_SCK_H() SMBUS_PORT->BSRR = SMBUS_SCK #define SMBUS_SCK_L() SMBUS_PORT->BRR = SMBUS_SCK #define SMBUS_SDA_H() SMBUS_PORT->BSRR = SMBUS_SDA #define SMBUS_SDA_L() SMBUS_PORT->BRR = SMBUS_SDA #define SMBUS_SDA_PIN() SMBUS_PORT->IDR & SMBUS_SDA void SMBus_StartBit(void) {
SMBUS_SDA_H(); // Set SDA line SMBus_Delay(8); // Wait a few microseconds SMBUS_SCK_H(); // Set SCL line SMBus_Delay(8); // Generate bus free time between Stop SMBUS_SDA_L(); // Clear SDA line
SMBus_Delay(8); // Hold time after (Repeated) Start
// Condition. After this period, the first clock is generated.
//(Thd:sta=4.0us min)
SMBUS_SCK_L(); // Clear SCL line
SMBus_Delay(8); // Wait a few microseconds
}
void SMBus_StopBit(void)
{
SMBUS_SCK_L(); // Clear SCL line
SMBus_Delay(8); // Wait a few microseconds
SMBUS_SDA_L(); // Clear SDA line
SMBus_Delay(8); // Wait a few microseconds
SMBUS_SCK_H(); // Set SCL line
SMBus_Delay(8); // Stop condition setup time(Tsu:sto=4.0us min)
SMBUS_SDA_H(); // Set SDA line
}
u8 SMBus_SendByte(u8 Tx_buffer)
{
u8 Bit_counter;
u8 Ack_bit;
u8 bit_out;
for(Bit_counter=8; Bit_counter; Bit_counter--)
{
if (Tx_buffer&0x80)
{
bit_out=1; // If the current bit of Tx_buffer is 1 set bit_out
}
else
{
bit_out=0; // else clear bit_out
}
SMBus_SendBit(bit_out); // Send the current bit on SDA
Tx_buffer<<=1; // Get next bit for checking
}
Ack_bit=SMBus_ReceiveBit(); // Get acknowledgment bit
return Ack_bit;
}
void SMBus_SendBit(u8 bit_out)
{
if(bit_out==0)
{
SMBUS_SDA_L();
}
else
{
SMBUS_SDA_H();
}
SMBus_Delay(6); // Tsu:dat = 250ns minimum
SMBUS_SCK_H(); // Set SCL line
SMBus_Delay(8); // High Level of Clock Pulse
SMBUS_SCK_L(); // Clear SCL line
SMBus_Delay(8); // Low Level of Clock Pulse
return;
}
u8 SMBus_ReceiveBit(void)
{
u8 Ack_bit;
SMBUS_SDA_H();
SMBus_Delay(6); // High Level of Clock Pulse
SMBUS_SCK_H(); // Set SCL line
SMBus_Delay(8); // High Level of Clock Pulse
if (SMBUS_SDA_PIN())
{
Ack_bit=1;
}
else
{
Ack_bit=0;
}
SMBUS_SCK_L(); // Clear SCL line
SMBus_Delay(8); // Low Level of Clock Pulse
return Ack_bit;
}
u8 SMBus_ReceiveByte(u8 ack_nack)
{
u8 RX_buffer;
u8 Bit_Counter;
for(Bit_Counter=8; Bit_Counter; Bit_Counter--)
{
if(SMBus_ReceiveBit()) // Get a bit from the SDA line
{
RX_buffer <<= 1; // If the bit is HIGH save 1 in RX_buffer
RX_buffer |=0x01;
}
else
{
RX_buffer <<= 1; // If the bit is LOW save 0 in RX_buffer
RX_buffer &=0xfe;
}
}
SMBus_SendBit(ack_nack); // Sends acknowledgment bit
return RX_buffer;
}
void SMBus_Delay(u16 time)
{
u16 i, j;
for (i=0; i<5; i++)
{
for (j=0; j<time; j++);
}
}
void SMBus_Init()
{
GPIO_InitTypeDef GPIO_InitStructure;
/* Enable SMBUS_PORT clocks */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_SMBUS_PORT, ENABLE);
/*??SMBUS_SCK?SMBUS_SDA????????*/
GPIO_InitStructure.GPIO_Pin = SMBUS_SCK | SMBUS_SDA;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_OD;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(SMBUS_PORT, &GPIO_InitStructure);
SMBUS_SCK_H();
SMBUS_SDA_H();
}
u16 SMBus_ReadMemory(u8 slaveAddress, u8 command)
{
u16 data; // Data storage (DataH:DataL)
u8 Pec; // PEC byte storage
u8 DataL=0; // Low data byte storage
u8 DataH=0; // High data byte storage
u8 arr[6]; // Buffer for the sent bytes
u8 PecReg; // Calculated PEC byte storage
u8 ErrorCounter; // Defines the number of the attempts for communication with MLX90614
ErrorCounter=0x00; // Initialising of ErrorCounter
slaveAddress <<= 1; //2-7???????
do
{
repeat:
SMBus_StopBit(); //If slave send NACK stop comunication
--ErrorCounter; //Pre-decrement ErrorCounter
if(!ErrorCounter) //ErrorCounter=0?
{
break; //Yes,go out from do-while{}
}
SMBus_StartBit(); //Start condition
if(SMBus_SendByte(slaveAddress))//Send SlaveAddress ???Wr=0????????
{
goto repeat; //Repeat comunication again
}
if(SMBus_SendByte(command)) //Send command
{
goto repeat; //Repeat comunication again
}
SMBus_StartBit(); //Repeated Start condition
if(SMBus_SendByte(slaveAddress+1)) //Send SlaveAddress ???Rd=1????????
{
goto repeat; //Repeat comunication again
}
DataL = SMBus_ReceiveByte(ACK); //Read low data,master must send ACK
DataH = SMBus_ReceiveByte(ACK); //Read high data,master must send ACK
Pec = SMBus_ReceiveByte(NACK); //Read PEC byte, master must send NACK
SMBus_StopBit(); //Stop condition
arr[5] = slaveAddress; //
arr[4] = command; //
arr[3] = slaveAddress+1; //Load array arr
arr[2] = DataL; //
arr[1] = DataH; //
arr[0] = 0; //
PecReg=PEC_Calculation(arr);//Calculate CRC
}
while(PecReg != Pec); //If received and calculated CRC are equal go out from do-while{}
data = (DataH<<8) | DataL; //data=DataH:DataL
return data;
}
u8 PEC_Calculation(u8 pec[])
{
u8 crc[6];
u8 BitPosition=47;
u8 shift;
u8 i;
u8 j;
u8 temp;
do
{
/*Load pattern value 0x000000000107*/
crc[5]=0;
crc[4]=0;
crc[3]=0;
crc[2]=0;
crc[1]=0x01;
crc[0]=0x07;
/*Set maximum bit position at 47 ( six bytes byte5...byte0,MSbit=47)*/
BitPosition=47;
/*Set shift position at 0*/
shift=0;
/*Find first "1" in the transmited message beginning from the MSByte byte5*/
i=5;
j=0;
while((pec[i]&(0x80>>j))==0 && i>0)
{
BitPosition--;
if(j<7)
{
j++;
}
else
{
j=0x00;
i--;
}
}/*End of while */
/*Get shift value for pattern value*/
shift=BitPosition-8;
/*Shift pattern value */
while(shift)
{
for(i=5; i<0xFF; i--)
{
if((crc[i-1]&0x80) && (i>0))
{
temp=1;
}
else
{
temp=0;
}
crc[i]<<=1;
crc[i]+=temp;
}/*End of for*/
shift--;
}/*End of while*/
/*Exclusive OR between pec and crc*/
for(i=0; i<=5; i++)
{
pec[i] ^=crc[i];
}/*End of for*/
}
while(BitPosition>8); /*End of do-while*/
return pec[0];
}
float SMBus_ReadTemp(void)
{
return (SMBus_ReadMemory(SA, RAM_ACCESS|RAM_TOBJ1)*0.02-273.15);
}
mlx90614.h
/********************************************************************************************************** author: 芯晟科电子&offical date : 2020/05/10 address: copyright : 2020-2030 **********************************************************************************************************/
#ifndef __MLX90614_H
#define __MLX90614_H
#include "stm32f10x.h"
void SMBus_StartBit(void);
void SMBus_StopBit(void);
void SMBus_SendBit(u8);
u8 SMBus_SendByte(u8);
u8 SMBus_ReceiveBit(void);
u8 SMBus_ReceiveByte(u8);
void SMBus_Delay(u16);
void SMBus_Init(void);
u16 SMBus_ReadMemory(u8, u8);
u8 PEC_Calculation(u8*);
float SMBus_ReadTemp(void); //获取温度值
#endif
4.实验结果
仅管BAA型号的传感器价格已经十分昂贵，但与医用级别的差距还很大，而且其对距离的要求比较高，小于1cm才会相对准确。将代码编绎后下载到开发板中，将手腕贴于传感器探头的表面，测出来的温度如图所示。