Digital Pot

[Scott]

I am looking at building a test board that using a Digital potentiometer such as the Analog devices AD5160 or the Microchip MCP42XXX to simulate a 10k ohm thermistor via software.

Can someone give me some pointers?
Has anyone attempted anything like this?

Any help would be great,
Scott

[mister_e]

Digital pot is one option BUT there's probably cheaper way to do it depending on how the Thermistor is place in the circuit. Generating a coltage with PWM and a op-amp buffer could do the same job.

BTW do you have a schematic of the Thermistor section you want to simulate?

[Scott]

Voltage will be supplied by another I/O board. I want to vary the resistance to simulate the changing of the temperature with the digital potentiometer. Does this make sense? I would like to place the board that will be simulating the 10k ohm thermistor in the same location as the real 10k ohm thermistor.

I am trying to simulate earlier captured data.

I do not have a schematic for the sensor!

Thanks,
Scott

[mister_e]

Sure it make sense no problem. Yes you can use Digital pot for that but you'll be limited to their own position/taps limitation.

Good luck.

[CocaColaKid]

Here's the code I wrote to control 5 digital pots daisy chained together.

DEFINE  LOADER_USED 1   ' Bootloader is being used
DEFINE  OSC 16          ' Set oscillator frequency, 4MHz (HS_PLL x4)
DEFINE  HSER_BAUD 9600  ' Baud rate for serial output
DEFINE  HSER_CLROERR 1  ' Automatically clear over-run errors
DEFINE  HSER_RCSTA 90h	' Enable USART receive
DEFINE  HSER_TXSTA 24h	' TXSTA=%00100100. TX enable, BRGH=1 for high-speed

@ __CONFIG _CONFIG1H, _OSCS_OFF_1H & _HSPLL_OSC_1H
' Oscillator Switch Disable
' Oscillator Type HS PLL    
 
@ __CONFIG _CONFIG2L, _BOR_ON_2L & _PWRT_ON_2L & _BORV_45_2L
' Brown-Out Reset Enabled
' Power-Up Timer Enable
' Brown-Out Reset Voltage 4.5V

@ __CONFIG _CONFIG2H, _WDT_ON_2H 
' Watch Dog Timer Enable

@ __CONFIG _CONFIG4L, _STVR_ON_4L & _LVP_OFF_4L & _DEBUG_OFF_4L
' Stack Over/Underflow Reset Enable
' Low Voltage ICSP Programming Disabled
' Background Debugger Disabled

    ADCON1 = %0111              ' Set porta to digital mode

    si      var     porte.2
    sclk    var     porte.1
    cs      var     porte.0

    pot_value_0 var     byte
    pot_value_1 var     byte
    pot_value_2 var     byte
    pot_value_3 var     byte
    pot_value_4 var     byte
    cmd         var     byte
    position    var     byte

    low     sclk    ' Set clock pin low
    high    cs      ' Set chip select low

    clear
    
start:
    gosub pot_5
    gosub pot_4
    gosub pot_3
    gosub pot_2
    gosub pot_1
    goto start                      

pot_5:
    low cs
    cmd = %00010001 : position = pot_value_4 : gosub shout
    cmd = 0 : position = 0 : gosub shout
    cmd = 0 : position = 0 : gosub shout
    high cs
    return

pot_4:
    low cs
    cmd = %00010010 : position = pot_value_3 : gosub shout
    cmd = 0 : position = 0 : gosub shout
    high cs
    return

pot_3:
    low cs
    cmd = %00010001 : position = pot_value_2 : gosub shout
    cmd = 0 : position = 0 : gosub shout
    high cs
    return

pot_2:
    low cs
    cmd = %00010010 : position = pot_value_1 : gosub shout
    high cs
    return

pot_1:
    low cs
    cmd = %00010001 : position = pot_value_0 : gosub shout
    high cs
    return

shout:
    shiftout si,sclk,1,[cmd]
    shiftout si,sclk,1,[position]
    return

Just set the pot_value_x to whatever you want between 0-255.

[Scott]

Wow!

Thanks for the code I'll give it a try this week and let you know.

Scott

[CocaColaKid]

If you need any help with them just give me a shout.