Voltages on A to D inputs of PIC 16C770

Discussion in 'Embedded Systems and Microcontrollers' started by beenthere, Aug 18, 2006.

  1. beenthere

    Thread Starter Retired Moderator

    Apr 20, 2004
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    Hi All,

    I've been trying to use a Dataq DI-154RS to do some datalogging. With very little success. The device has four input channels for A to D conversion. Even with the inputs shorted, there is several bits of noise. Working with a signal is even worse. Using a very quiet voltage source, it still sees over 100 millivolts of noise. Monitoring the same signal with a meter shows no noise down to the millivolt level.

    The active device inside is a PIC 16C770. With no input, each line in shows 3.3 volts. My meter sees the 3.3 volts at the input terminals. This falls to .33 volts when the device is not active, but powered up.

    I have not been able to get the datasheet to load down from Microchip. Does anybody have any experience with this device? Is this one broken, or are they really this horrible? I just can't imagine a piece of test equipment that injects a voltage artifact into the input.
     
  2. Dave

    Retired Moderator

    Nov 17, 2003
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    Hi beenthere,

    Apologies I have have no personal experience with this device. Do you have access to other test equipment where you could check to see if your observations on this particular PIC device are present there? The datasheet for the Dataq equipment doesn't appear to throw any light on you situation.

    Incidently, I was able to download the datasheet for the said MC from this link.

    Dave
     
  3. beenthere

    Thread Starter Retired Moderator

    Apr 20, 2004
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    Hi Dave,

    The voltage is probably leakage occuring when the pins are not configured for inputs to the A to D. I just wanted confirmation.

    Thanks for the link, but no luck. I have to haul my computer into the school where I volunteer and put it on a T1 line to get updates. I'm still running Adobe 6, and 7.08 is now the latest and greatest. Adobe has seemingly abandoned backwards compatability. At least I'm up to XP so I can install it.
     
  4. Dave

    Retired Moderator

    Nov 17, 2003
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    Agreed I have noticed some inconsistencies with Acrobat 6 when looking at PDFs on the web. Have you looked at a newsgroup to see if anyone has come across your problem? I'm sure Microchip have a newsgroup you could subscribe to, to see if anyone has experienced this before.

    Dave
     
  5. beenthere

    Thread Starter Retired Moderator

    Apr 20, 2004
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    Hi Dave,

    Adobe 7.08 in place, and pdf's noe load faultlessly. Looks like off-state leakage.

    Lesson: Whaddya want for $24.95?

    Too bad the device is a bit less awesome than the spec sheet.
     
  6. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
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    Lol, sold a dud one! Been had a few times myself. Suppose you've learnt something from this experience.

    Dave
     
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