Digital Potentiometer

Discussion in 'General Electronics Chat' started by ELECTRONERD, Jun 17, 2009.

  1. ELECTRONERD

    Thread Starter Senior Member

    May 26, 2009
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    Hey Everyone,

    Could someone explain to me how a digital potentiometer works and how I could use it?

    Thanks!
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Gee, that's a mighty general question.

    But basically, you supply a digital pot with voltages for both "ends" (sometimes labeled H and L for high and low) and you get a voltage between those two at the "wiper" (sometimes labeled "W") depending upon the binary input that you supply it.

    Some digital pots use parallel binary data, some use serial binary data. Also, the "H", "L" and "W" terminals are usually limited to the range of the digital pots' supply voltages.

    How can you use it? Lots of ways. Usually for establishing some kind of low-current reference voltage or input to an opamp or other high-impedance circuit.
     
  3. ELECTRONERD

    Thread Starter Senior Member

    May 26, 2009
    1,146
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    Yeah, I thought that was how it worked, but when I look at some of the digital potentiometer IC's they dont seem to work that way... They dont have switches for the "High" and "Low."
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Those aren't switches; they are the opposite "ends" of the digital pot.

    Some pots might just use the pots' own Vcc/Vdd and GND terminals instead of having external H and L connections.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    The data sheets usually have the circuit shown.
     
  6. ELECTRONERD

    Thread Starter Senior Member

    May 26, 2009
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    Okay, I'll have to look at it again. Thanks!
     
  7. Tobias

    Active Member

    May 19, 2008
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    0
    Just look at it as a mechanical pot that is controlled by a PIC, STAMP, etc. Instead of you turning the dial to change the resistance between Leg1/Wiper and Leg2/Wiper, the processor does it for you. You will find the digital pots in 256, 512, or 1024 steps most likely. That number will give you a resolution. You have already noticed I am sure that you can find 10k, 20k etc digital pots. The steps is how many parts the range is divided. For example, you have a 10k pot with 256 steps. Each step is 10k/256.

    The pots have a couple different protocols to issue a command. The most basic is the 'step' type. I think that's the name. I use them often yet can't remember what they are exactly called. Anyway, there are two inputs, High/Low and Increment. When the pot fires up it starts in the middle position. If 10k and 256 steps, then the wiper is at 5k. If the High/Low pin is HI and you send it one pulse, it will then be at 5k + (5k/256). Conversely High/Low pin is pulled low and one pulse, the result is 5k-(5k/256).

    There are a couple other formats to communicate with a digital pot. The steps are removed and you in essence tell the digital pot with one command to move the wiper to one spot on the 10k spectrum.

    You can wire the digital pot to not just output a voltage but take Leg1 and Wiper together as one along with Leg2 and you can literally vary resistance to a circuit. Make sure you tie Leg1 to the wiper. I learned that leaving it float will allow RF to really screw things up.
     
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