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MCP41010 - Not "Set and Forget" ? — Parallax Forums

MCP41010 - Not "Set and Forget" ?

John A. ZoidbergJohn A. Zoidberg Posts: 514
edited 2011-02-27 18:08 in General Discussion
Hello there,

I bought these Microchip's MCP41010 digital potentiometers some two years ago, and I totally forgotten about them until I searched my drawers.

So, I tested them since I will be planning to make it as a digital voltage reference. However, when I punched in the values and go to the next subroutine, the output went back to 1/2 the voltage supply!

I had to keep sending the values into the chip repeatedly to maintain the desired voltage output.

I believe it is not "set and forget"? If that is not - any good non-volatile digital potentiometers to recommend? Through hole is the best one. :)

Comments

  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2011-02-27 08:02
    From the first page of the data sheet ... "The wiper is reset to the mid-scale position (80h) upon power-up. The RS (reset) pin implements a hardware reset and also returns the wiper to mid-scale." ... the mid-position reseting sounds like what you are experiencing. How do you have the MCP41010 configured, and what does the code that you are using look like?

    Reference:
    http://ww1.microchip.com/downloads/en/devicedoc/11195c.pdf
  • John A. ZoidbergJohn A. Zoidberg Posts: 514
    edited 2011-02-27 08:12
    Beau Schwabe (Parallax) wrote: »
    From the first page of the data sheet ... "The wiper is reset to the mid-scale position (80h) upon power-up. The RS (reset) pin implements a hardware reset and also returns the wiper to mid-scale." ... the mid-position reseting sounds like what you are experiencing. How do you have the MCP41010 configured, and what does the code that you are using look like?

    Reference:
    http://ww1.microchip.com/downloads/en/devicedoc/11195c.pdf

    I've checked the datasheet - this is the MCP41010 and it has only one potentiometer inside and nothing else.

    There is also no reset pin on the chip, only 3 SPI lines (/CS, DI, CLK), two voltage pins (VDD and VSS) and finally, two potentiometer terminals and one wiper pin.

    I do not think that this thing ever remembers the last one after I punched in the values inside.

    Or I may be missing out on something?
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2011-02-27 08:42
    I would still be curious to see the schematic and code that you are using ... On power up, the MCP41010 defaults to mid-wiper position. If somehow the power supply is not adequate or not correct it might cause symptoms of what you are describing. Also, you can enter into a shut down mode on the MCP41010 through software, so there could be a problem there.
  • John A. ZoidbergJohn A. Zoidberg Posts: 514
    edited 2011-02-27 18:08
    Beau Schwabe (Parallax) wrote: »
    I would still be curious to see the schematic and code that you are using ... On power up, the MCP41010 defaults to mid-wiper position. If somehow the power supply is not adequate or not correct it might cause symptoms of what you are describing. Also, you can enter into a shut down mode on the MCP41010 through software, so there could be a problem there.

    Sorry for late reply. I will be drawing the schematic and post the code here later, I'm at my own university working in the office.

    The funny thing is, I managed to get it to "set and forget" by first sending a empty/dummy data first, then send the desired command and value again.

    Also, the strange thing is, I haven't ever sent dummy data to DS1307s before or any other SPI related peripherals.

    Any explaination on this? :)
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