program IR_Thermometer

' * IR_Thermometer
' * Copyright C.TAVERNIER- 2010
' * for Elektor Magazine
' * www.tavernier-c.com
' *
' * Microchip PIC16F876A and
' * Melexis MLX90614 IR Thermometer

' LCD module connections
' LCD used in 4 bits mode on Port B

dim LCD_RS as sbit  at RB2_bit
    LCD_EN as sbit  at RB3_bit
    LCD_D4 as sbit  at RB4_bit
    LCD_D5 as sbit  at RB5_bit
    LCD_D6 as sbit  at RB6_bit
    LCD_D7 as sbit  at RB7_bit

    LCD_RS_Direction as sbit at TRISB2_bit
    LCD_EN_Direction as sbit at TRISB3_bit
    LCD_D4_Direction as sbit at TRISB4_bit
    LCD_D5_Direction as sbit at TRISB5_bit
    LCD_D6_Direction as sbit at TRISB6_bit
    LCD_D7_Direction as sbit at TRISB7_bit

' End LCD module connections

' Variable definitions

dim SensorLow as byte       ' Raw temp. low byte
    SensorHigh as byte      ' Raw temp. high byte
    SensorRaw as word       ' Raw temp. word
    SensorRawCur as word    ' Current raw temp.
    SensorRawMax as word    ' Max. raw temp.
    SensorRawMin as word    ' Min. raw temp.
    Sensor as float         ' Real temp (floating point)
    SensorString as string[9]
    DisplayString as string[9]
    PEC as byte             ' Control byte (read but not used)
    com as byte             ' MLX90614 command
    PosDecPoint as byte     ' Decimal point position
    i as byte

' Procedure definition

' Read Temperature From MLX90614
' Input : com specify temp. to read
' Output : raw temp as a word

  Sub procedure Read_temp(dim com as byte)

  I2C1_Start()           ' issue I2C start signal
  I2C1_Wr(0x00)          ' send address (device address + W)
  I2C1_Wr(com)           ' send command
  I2C1_Repeated_Start()  ' issue I2C signal repeated start
  I2C1_Wr(0x01)          ' send address (device address + R)
  SensorLow = I2C1_Rd(1) ' Read temp. low byte (acknowledge)
  SensorHigh = I2C1_Rd(1)' Read temp. high byte (acknowledge)
  PEC = I2C1_Rd(1)       ' Read PEC (not used) (acknowledge)
  I2C1_Stop()            ' issue I2C stop signal
  SensorRaw = SensorLow + (SensorHigh << 8)     ' Build temp. word

  End sub

' Convert raw data in SensorRaw
' to displayable string in DisplayString

  Sub procedure Convert_raw

  Sensor = SensorRaw * 0.02 - 273.15            ' Raw temp to Celsius
  FloatToStr (Sensor, SensorString)             ' Float to string
  PosDecPoint = Strchr (SensorString,".")       ' Search for dec. point
  For i = 0 to PosDecPoint+2                    ' Limit display to two digits
      DisplayString[i] = SensorString[i]        ' after decimal point
  Next i
  DisplayString[PosDecPoint+3]= ""
  DisplayString = DisplayString + " C"
  
  End sub

' Main Program

main:

' Initialize I/O

  PORTB = 0
  TRISB = 0                      ' All PORTB lines as output
  ADCON1  = 0x0F                 ' Configure AN pins as digital I/O

' Initialize LCD display

  Lcd_Init()                     ' Initialize Lcd
  Lcd_Cmd(_LCD_CLEAR)            ' Clear display
  Lcd_Cmd(_LCD_CURSOR_OFF)       ' Cursor off

' Initialize Min and Max object temp.

  SensorRawMax = 0
  SensorRawMin = 0xFFFF

' Initialize SMBus

  I2C1_Init(100000)              ' I2C/SMBus Clock speed 100 kHz
  SETBIT (SSPSTAT,6)             ' Force MSSP in SMBus mode

while true

    Read_temp (0x06)             ' Read ambiant temp.

    Convert_raw

    Lcd_Out(1,1,"T Amb. : ")     ' Write ambiant temp in first row
    Lcd_Out(1,10,DisplayString)

    Read_temp (0x07)             ' Read object temp.

    SensorRawCur = SensorRaw     ' Make obj. temp. current temp.
    
    If SensorRawCur > SensorRawMax Then ' Is current temp. higher than max. temp.
       SensorRawMax = SensorRawCur      ' Make max. temp. equal current temp.
    End if

    If SensorRawCur < SensorRawMin Then ' Is current temp. lower than min. temp.
       SensorRawMin = SensorRawCur      ' Make min. temp. equal current temp.
    End if

    Convert_raw

    Lcd_Out(2,1,"T Obj. : ")     ' Write object temp in second row
    Lcd_Out(2,10,DisplayString)
    
    SensorRaw = SensorRawMax
    Convert_raw

    Lcd_Out(3,1,"T Max. : ")     ' Write Max object temp in third row
    Lcd_Out(3,10,DisplayString)

    SensorRaw = SensorRawMin
    Convert_raw

    Lcd_Out(4,1,"T Min. : ")     ' Write Min object temp in fourth row
    Lcd_Out(4,10,DisplayString)

    Delay_ms (1000)

wend

end.