Digital Pot

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

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?

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

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.

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

Code:

---

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.

Wow!

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

Scott

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