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Thread: teensy 3.1 'ground' pins

  1. #1
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    teensy 3.1 'ground' pins

    The schematic indicates an analog ground, which is connected to power return through an L and three ground pins that use the power equipotential symbol.

    The pin-out diagram indicates 'AGND' where the silkscreen also indicates 'AGND', a 'GND' pin where the silkscreen indicates 'G', and another 'GND' pin where the silk screen indicates '6'.

    Measurements indicate that the pin with the silkscreen markings 'GND' is power return, but does not connect to any other ground; and 'AGND' is connected to the 'G' pin; while pin 6 is not connected to any other ground.

    1. Does the end-use provide the mecca for joining the grounds?
    2. Is there a recommended usage for each of these ground pins?

    Thanks much.

  2. #2
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    Ignore this post #2; it is superceded by post #4 below which clarifies that there are no errors, just an non-obvious layout of the paper crib sheet...

    I think the paper printed pins crib sheet for Teensy 3.0 and 3.1 has an error for pin 6. On the board bottom side crib sheet card, pin 6 may be incorrectly marked GND. On the top side it is shown as configurable for a PWM or CS2.
    The Teensy 3.0 schematic I found shows pin 6 connected to the CPU's PTD4, a digital I/O pin.
    See enclosure.
    The silk screen on the board for T3.0 and T3.1 seems correct.

    the correction would be to remove the annotation GND at pin 6 from the pins crib sheets for 3.0 and 3.1.
    Click image for larger version. 

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    GND on the short edge of the card has continuity to the pin hole named GND which is adjacent to pin #0. So either can be use for the power return ground.

    Analog ground is isolated to reduce noise, as is commonly done.
    Last edited by stevech; 01-31-2014 at 11:11 PM.

  3. #3
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    On the paper card, the labels on the back side are referring to the "inner" connections, the front side labels refer to the outer connections. The GND label is referring to the GND surface mount pad. Same for all the other labels.

  4. #4
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    Quote Originally Posted by nox771 View Post
    On the paper card, the labels on the back side are referring to the "inner" connections, the front side labels refer to the outer connections. The GND label is referring to the GND surface mount pad. Same for all the other labels.
    sorry... I see it now. Never noticed that. The words annotated on the paper sheet for the BOTTOM side are the functions of the rectangular copper pads, not the pin holes.
    Yikes. Never noticed that. Something should be added to the crib sheet to clarify.

    so the GND annotation adjacent to pin 6 refers to the pad marked GND in the silk screen. As does the annotation A12 to the right of GND. And so on.
    Last edited by stevech; 01-31-2014 at 11:12 PM.

  5. #5
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by stevech View Post
    Yikes. Never noticed that. Something should be added to the crib sheet to clarify.
    D'oh, another batch of cards just finished printing.

    Any suggestions for what ought to be printed on the next batch?

  6. #6
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    Good People,

    Thanks much for the replies - still confused, but I see what is meant by "inner" and "outer", makes sense.

    As for an "isolated" ground, not certain what this means. According to schematic, no galvanic barrier indicated, so cannot assume any isolation. Perhaps alluding to practices for routing of traces to control return Z and current flow, and the use of L and/or C to decouple analog from digital from power equipotential references.

    Still not certain about:
    1. Does the end-use provide the mecca for joining the grounds?
    2. Is there a recommended usage for each of these ground pins?

    Until I receive an authoritative reply, will just have to provide separate returns and hope for the best. If I am wrong, could see a 3.1 board smoke tonight.

    thanks much.

    Edit:
    One of the gnd pins had no connection to my board because the header plastic was missing a pin - I will take fingerprints and DNA samples, then send the perp to Northern Afghanistan to wind power transformers on the side of a mountain using scrapped phone wire and bare hack-saw blades, for at least 2 years.
    Last edited by BJB; 02-02-2014 at 10:05 PM.

  7. #7
    Senior Member PaulStoffregen's Avatar
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    If it doubt, use the GND pins (any or all of them).

    AGND is normally only used to connect the ground for analog signals. For example, if you have a sensor that output an analog voltage, connect its ground to AGND. Or a pot would normally connect to AGND. But don't worry too much if you connect to GND instead of AGND. Usually it makes little or no difference.

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