Hey all I have been playing with a number of different Sigma Delta ADC's. This time its a 24-bit offering from Linear Tech - LTC2410. Overall, its super easy to work with and much easier than the I2C MCP3421. See code below for details. I have also uploaded a picture of the digital scale I hacked apart and interfaced to using a development board and a pickit2.



Code:
'****************************************************************
'*  Name    : UNTITLED.BAS                                      *
'*  Author  : [select VIEW...EDITOR OPTIONS]                    *
'*  Notice  : Copyright (c) 2011 [select VIEW...EDITOR OPTIONS] *
'*          : All Rights Reserved                               *
'*  Date    : 6/9/2011                                          *
'*  Version : 1.0                                               *
'*  Notes   :                                                   *
'*          :                                                   *
'****************************************************************
'References
'Arduino - http://interface.khm.de/index.php/lab/experiments/connect-a-ltc2400-high-precision-24-bit-analog-to-digital-converter/
'Datasheet - http://cds.linear.com/docs/Datasheet/2410fs.pdf
;-------------------------------------------------------------------------------
Device = 18F26K22
    Xtal = 10
    Declare PLL_Req = On    
    All_Digital = TRUE
;-------------------------------------------------------------------------------
;**** Added by Fuse Configurator ****
; Use the Fuse Configurator plug-in to change these settings

Declare Reminders Off
@ CONFIG_REQ = 0 ; Override Compiler's configuration settings
Asm-
    Config FOSC = HSMP	;HS oscillator (medium power 4-16 MHz)
    Config PLLCFG = On	;Oscillator multiplied by 4
    Config PRICLKEN = On	;Primary clock enabled
    Config FCMEN = OFF	;Fail-Safe Clock Monitor disabled
    Config IESO = OFF	;Oscillator Switchover mode disabled
    Config PWRTEN = OFF	;Power up timer disabled
    Config BOREN = SBORDIS	;Brown-out Reset enabled in hardware only (SBOREN is disabled)
    Config BORV = 190	;VBOR set to 1.90 V nominal
    Config WDTEN = OFF	;Watch dog timer is always disabled. SWDTEN has no effect.
    Config WDTPS = 256	;1:256
    Config CCP2MX = PORTC1	;CCP2 input/output is multiplexed with RC1
    Config PBADEN = OFF	;PORTB<5:0> pins are configured as digital I/O on Reset
    Config CCP3MX = PORTB5	;P3A/CCP3 input/output is multiplexed with RB5
    Config HFOFST = On	;HFINTOSC output and ready status are not delayed by the oscillator stable status
    Config T3CMX = PORTC0	;T3CKI is on RC0
    Config P2BMX = PORTB5	;P2B is on RB5
    Config MCLRE = EXTMCLR	;MCLR pin enabled, RE3 input pin disabled
    Config STVREN = On	;Stack full/underflow will cause Reset
    Config LVP = On	;Single-Supply ICSP enabled if MCLRE is also 1
    Config XINST = OFF	;Instruction set extension and Indexed Addressing mode disabled (Legacy mode)
    Config Debug = OFF	;Disabled
    Config CP0 = OFF	;Block 0 (000800-003FFFh) not code-protected
    Config CP1 = OFF	;Block 1 (004000-007FFFh) not code-protected
    Config CP2 = OFF	;Block 2 (008000-00BFFFh) not code-protected
    Config CP3 = OFF	;Block 3 (00C000-00FFFFh) not code-protected
    Config CPB = OFF	;Boot block (000000-0007FFh) not code-protected
    Config CPD = OFF	;Data EEPROM not code-protected
    Config WRT0 = OFF	;Block 0 (000800-003FFFh) not write-protected
    Config WRT1 = OFF	;Block 1 (004000-007FFFh) not write-protected
    Config WRT2 = OFF	;Block 2 (008000-00BFFFh) not write-protected
    Config WRT3 = OFF	;Block 3 (00C000-00FFFFh) not write-protected
    Config WRTC = OFF	;Configuration registers (300000-3000FFh) not write-protected
    Config WRTB = OFF	;Boot Block (000000-0007FFh) not write-protected
    Config WRTD = OFF	;Data EEPROM not write-protected
    Config EBTR0 = OFF	;Block 0 (000800-003FFFh) not protected from table reads executed in other blocks
    Config EBTR1 = OFF	;Block 1 (004000-007FFFh) not protected from table reads executed in other blocks
    Config EBTR2 = OFF	;Block 2 (008000-00BFFFh) not protected from table reads executed in other blocks
    Config EBTR3 = OFF	;Block 3 (00C000-00FFFFh) not protected from table reads executed in other blocks
    Config EBTRB = OFF	;Boot Block (000000-0007FFh) not protected from table reads executed in other blocks
Endasm-
Declare Reminders On
;**** End of Fuse Configurator Settings ****
;-------------------------------------------------------------------------------      
' ** Declare Pins Used **
	Symbol CS   = PORTB.0				' Chip Select Pin
	Symbol SDO  = PORTB.1				' Shift Data Pin 
	Symbol SCK	= PORTB.2				' Shift Clock Pin 
;------------------------------------------------------------------------------- 
' ** Declare Variables **     
    Symbol VREF = 5.0                   ' Vref in Volts
    Dim RAW As Dword                    ' RAW value read from ADC
    Dim SIGN As Dword                   ' Sign Value for Negative Numbers
    Dim COUNTS As Dword                 ' 24-Bit Counts Variable
    Dim VOLTS  As Float                 ' Volts value
    Dim READY As Bit                    ' Ready Bit for conversion completion
;------------------------------------------------------------------------------- 
' ** MAIN **    
;------------------------------------------------------------------------------- 
MAIN:
    GoSub GET_SAMPLE

    If READY = 1 Then
        GoSub CONVERT_SAMPLE
    EndIf 
    SerOut PORTB.7,84,[13,10] 
    DelayMS 250
GoTo MAIN
;------------------------------------------------------------------------------- 
' ** SUB ROUTINES **    
;-------------------------------------------------------------------------------
GET_SAMPLE: 'INPUT - N/A 
            'RETURN - RAW as DWORD

    Low CS 'Request Device Conversion
        If SDO = 1 Then ' Test if Device is ready
            READY = 1
            SHIn SDO,SCK,MsbPre_L,[RAW.Byte3,RAW.Byte2,RAW.Byte1,RAW.Byte0]
        Else
            READY = 0
            DelayMS 100 'Wait for Conversion to complete
            SerOut PORTB.7,84,["Conversion not Complete",13,10]
        EndIf 
    High CS 'Request Device to Sample
Return 
;-------------------------------------------------------------------------------
CONVERT_SAMPLE: 'INPUT - RAW as DWORD
                'RETURN - VOLTS as Float
                'RETURN - COUNTS as Float
    COUNTS = RAW
    SerOut PORTB.7,84,["0-",Bin32 COUNTS,32,SDec COUNTS,13,10]
    
    
    'Test for Overanging & Pos/Neg Values
    If RAW.29 = 1 Then
        If RAW.28 = 1 Then
            SerOut PORTB.7,84,["Over Range VIN >= 0.5 * VREF",13,10]  
        Else
            COUNTS = COUNTS
            SIGN = 1
        EndIf
    Else If RAW.29 = 0 Then
        If RAW.28 = 0 Then
            SerOut PORTB.7,84,["Under Range VIN <= 0.5 * VREF",13,10]  
        Else
            COUNTS = ~COUNTS 'Invert Sample
            SIGN = -1        'Apply Negative sign in final calculation
        EndIf
    EndIf
    SerOut PORTB.7,84,["1-",Bin32 COUNTS,32,SDec COUNTS,13,10] ' 
    
    COUNTS.31 = 0 'EOC Bit
    COUNTS.30 = 0 'Dummy Bit
    COUNTS.29 = 0 'Sign Bit
    SerOut PORTB.7,84,["2-",Bin32 COUNTS,32,SDec COUNTS,13,10] 

    COUNTS.4 = 0 'Sub LSBs
    COUNTS.3 = 0 'Sub LSBs
    COUNTS.2 = 0 'Sub LSBs
    COUNTS.1 = 0 'Sub LSBs
    COUNTS.0 = 0 'Sub LSBs

    SerOut PORTB.7,84,["3-",Bin32 COUNTS,32,SDec COUNTS,13,10] 
    COUNTS = COUNTS >> 5
    SerOut PORTB.7,84,["4-",Bin32 COUNTS,32,SDec COUNTS,13,10] 
   
    COUNTS = SIGN * COUNTS  'Apply Pos/Neg Sign Convention
    SerOut PORTB.7,84,["5-",Bin32 COUNTS,32,SDec COUNTS,13,10] 
    
    VOLTS = COUNTS * VREF / 16777216.0 '24-BIT RESOLUTION
    SerOut PORTB.7,84,["6 - ",Dec8 VOLTS," (V)",13,10]
Return


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