MCP9800 Temperature Sensor Interface

The MCP9800 digital temperature sensor converts temperatures between -55°C and +125°C. It provides an accuracy of ±1°C (maximum) from -10°C to +85°C. Interfacing to it is very straightforward via an I2C bus, especially with the Positron8 BASIC Compiler's, built in, I2C routines.

The MCP9800 datasheet can be downloaded from here: MCP9800.pdf

A suitable circuit for the MCP9800 temperature sensor is shown below:

The Positron8 BASIC code for the interface is shown below:

' Interface to an MCP9800 temperature sensor

' Transmits the temperature (in degrees Centigrade) to the serial terminal

'

' For the Amicus18 board, which uses a PIC18F25K20 device operating at 64MHz

' Written by Les Johnson for the Positron8 BASIC Compiler

'

   Include "Amicus18.inc"             ' Configure the compiler to use a PIC18F25K20 at 64MHz. i.e. An Amicus18 board

   Declare Float_Display_Type = Fast  ' Set for faster and more accurate floating point displaying

   Declare SDA_Pin PORTB.1                                     ' Setup the I2C SDA pin

   Declare SCL_Pin PORTB.0                                     ' Setup the I2C SCL pin

'

' Create some constants for the MCP9800 device

'

$define cMCP9800_ADDRESS_WRITE       $90

$define cMCP9800_ADDRESS_READ        $91

$define cMCP9800_ALERT_ACTIVE_LOW    $00

$define cMCP9800_ALERT_ACTIVE_HIGH   $04

$define cMCP9800_COMP_MODE           $00

$define cMCP9800_CONFIGURATION       $01

$define cMCP9800_HYSTERESIS          $02

$define cMCP9800_INT_MODE            $02

$define cMCP9800_LIMITSET            $03

$define cMCP9800_ONESHOT_OFF         $00

$define cMCP9800_ONESHOT_ON          $80

$define cMCP9800_SHUTDOWN_OFF        $00

$define cMCP9800_SHUTDOWN_ON         $01

$define cMCP9800_TEMPERATURE         $00

$define cMCP9800_TSET_DEFAULT        $50

$define cMCP9800_CONFIG_BITS         $64

$define cMCP9800_RES_9bit            $00

$define cMCP9800_RES_10bit           $20

$define cMCP9800_RES_11bit           $40

$define cMCP9800_RES_12bit           $60

$define cMCP9800_FAULT_QUEUE_0       $00

$define cMCP9800_FAULT_QUEUE_2       $08

$define cMCP9800_FAULT_QUEUE_4       $10

$define cMCP9800_FAULT_QUEUE_6       $18

Symbol cMCP9800 = cMCP9800_ONESHOT_OFF | cMCP9800_RES_12bit | cMCP9800_FAULT_QUEUE_0 | cMCP9800_ALERT_ACTIVE_LOW | cMCP9800_COMP_MODE | cMCP9800_SHUTDOWN_OFF

'

' Create a variable for the demo

'

   Dim MCP_fTemperature As Float                               ' Holds the temperature

'-------------------------------------------------------------------------------

' Setup the MCP9800 device

' Input     : None

' Output    : None

' Notes     : None

'

Proc MCP9800_Init()

   BusOut cMCP9800_ADDRESS_WRITE, [cMCP9800_CONFIGURATION, cMCP9800]

   BusOut cMCP9800_ADDRESS_WRITE, [cMCP9800_TEMPERATURE]

EndProc

'--------------------------------------------------------------------------------

' Interface to an MCP9800 I2C temperature sensor

' Input     : None

' Output    : Returnsthe temperature (in degrees Centigrade)

' Notes     : None

'

Proc MCP9800_GetTemperature(), Float

   Dim wRaw As Word                    ' Used for reading data from the device

   BusIn cMCP9800_ADDRESS_READ,[wRaw.Byte0, wRaw.Byte1]

   Result = wRaw.SByte0

   If wRaw.15 = 1 Then

       Result = Result + 0.5

   EndIf

   If wRaw.14 = 1 Then

       Result = Result + 0.25

   EndIf

   If wRaw.13 = 1 Then

       Result = Result + 0.125

   EndIf

   If wRaw.12 = 1 Then

       Result = Result + 0.0625

   EndIf

EndProc

'--------------------------------------------------------------------------------

' The main program loop starts here

' Read the temperature and send the ASCII value to a serial terminal

'

Main:

   MCP9800_Init()

   Do

       MCP_fTemperature = MCP9800_GetTemperature()

       HRSOutLn "Temperature = ", Dec2 MCP_fTemperature

       DelayMS 500

   Loop

Below is the program running within the Proteus simulator:

The above simulation files can be downloaded from here:

MCP9800_Proteus_Design.zip