How to use digital potentiometer as variable resistance

Discussion in 'The Projects Forum' started by watha2, Jun 27, 2013.

  1. watha2

    Thread Starter New Member

    Jun 1, 2013
    Hello, my name is Watha.
    I have a project to measure the output voltage of Photovoltaic using adjustable resistance in digital potentiometer AD5260.
    I need to use the digpot as variable resistance.
    In an mechanical potentiometer, if I need to use it as variable resistance, I could let the pin A floating, wire pin W (Wiper) to the source (photovoltaic) and pin B to the Ground. Or I could tie the pin A and pin W together.
    However, it didn't work in this digital potentiometer. If I did it that way, the output voltage is max and didn't change.
    But if I wire pin A to the source, pin B to the ground, and use pin W as output voltage, it just means that I use the digpot as voltage divider. The voltage output is linear because as I said, it used as voltage divider. I want it to be used as variable resistance and the output supposed to be logarithmic.
    Is my circuit is wrong?
    Or do I need to modified the program so it could be used as variable resistance?

    Please help.

    I attached the skematic circuit when I used it as voltage divider.,d.bmk
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
    You have the SHDN, pin #6, pulled high. This disables the pot, to get it to work, pin #6 needs to be pulled low. This is shown in the data sheet by the line above the SHDN marking of pin #6. With pin #6 pulled high it stays at the last resistance setting it was set at.
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
    Shutdown is active low. With the pin pulled low, pin A is open circuit. See Table 5 on page 7.

    Page 16 has info on using the device as a rheostat. I'm not sure why you are having a problem.
    Last edited: Jun 28, 2013