Serial control of a digital pot?

[TonyA]

Hi,

I am searching for info and examples for controlling a digital pot serially using shiftout. I am using the pic18f452, and I'm not sure which digital pot to use. Any suggestions/info would be greatly appreciated.

Thank you,
TonyA

[mister_e]

those i already used in the past from Microchip
MCP42010, MCP42050,MCP42100, MCP41010,MCP41050,MCP4110.

[TonyA]

Hi,

Are there any examples of code around?

Thanks,
Tony

[mister_e]

Not where i am, but i could download the datasheet and try something somewhere today.

As i remind it wasn't too complicated. Maybe there's some example here already done. Do a search with the model i suggest, you may find something

[TonyA]

I appreciate that very much. I will try a search here.

Thanks again,
Tony

[mister_e]

O.K it's untested but it should work for any MCP4XXXX digital pot. Try it and post your results

    '
    '    Hardware configuration
    '    ======================
    TRISC=0
    
    '                      
    '    Hardware connection
    '    ===================
    CS          VAR PORTC.0
    CLK         VAR PORTC.1
    SI          VAR PORTC.2
    
    '   
    '    Variables definition 
    '    ===================
    Wiper       var byte
    
    '
    '    Constants definition 
    '    ====================
    MSBFIRST    CON 1              
    WriteOnPot0 con %00010001

    '
    '    Software/Hardware initialisation
    '    ================================
    cs = 1      ' disable MCP
    PAUSE 100   ' safe settle time
    
Start:
    for wiper = 0 to 255
        cs=0                                            ' enable 
        shiftout si,clk, MSBFIRST,[WriteOnPot0, WIPER]  ' Write to MCP
        cs = 1                                          ' Disable
        pause 10                                       
        next                                           
    goto start

Now connect PA0 too vcc, PB0 to GND and read the voltage on PW0 pin... is this working?

[TonyA]

Hi,

I appreciate that very much.

What is this constant doing : WriteOnPot0 con %00010001 ?

(I aplogize in advance if this is obvious, my brain is a little jumbled today).

I will be getting the digital chip in a few days and I will try this out and post results.

I'll be using an analog sensor read by the pic 18f452 using adcin. Then interpreting that analog reading for use in the "Wiper" variable. So as the analog sensor changes so will the digital pot.

Thank again,
TonyA

[mister_e]

This constant is the CommandByte needed by the chip. Read datasheet section 5, and look the figure 5-2.