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Pull up resistors.. — Parallax Forums

Pull up resistors..

ArchiverArchiver Posts: 46,084
edited 2004-01-26 15:29 in General Discussion
Hi,

I'm using the SRF08 (SONAR) with my BS2P. On the example it says to
pull up the inputs from the SRF08 to the stamp by hooking them up to
the 5V power supply with some resistors. I'm just wondering, what
is the point of doing that? I wired it without the resistors and it
seems to be working fine.. Is the actaully a reason to pull up the
inputs? Does it have something to do with accuracy? Because the
results I get are fairly inaccurate...

Thanks
James

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2004-01-26 14:35
    The SRF08 uses I2C to communicate with the Stamp -- the pull-ups are for
    the I2C buss. Usually 4.7k, though I hear that one customer (in an
    electrically noisy robot project) went down to 1K. I've never had to,
    I've been able to use 4.7K with BASIC Stamps and Javelin Stamps.

    This N&V article may help out:

    http://www.parallax.com/dl/docs/cols/nv/vol4/col/99.pdf

    -- Jon Williams
    -- Applications Engineer, Parallax
    -- Dallas Office


    Original Message
    From: James Dang [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=baIUV3uqUAxofbD6okiNK4ju-_ostASO9GsDEYoIzcVsMbOS30sAvb3Z8y6P6NfrbbijsePjtCNnDdZsEA]ensignkim113@y...[/url
    Sent: Monday, January 26, 2004 5:59 AM
    To: basicstamps@yahoogroups.com
    Subject: [noparse][[/noparse]basicstamps] Pull up resistors..


    Hi,

    I'm using the SRF08 (SONAR) with my BS2P. On the example it says to
    pull up the inputs from the SRF08 to the stamp by hooking them up to
    the 5V power supply with some resistors. I'm just wondering, what
    is the point of doing that? I wired it without the resistors and it
    seems to be working fine.. Is the actaully a reason to pull up the
    inputs? Does it have something to do with accuracy? Because the
    results I get are fairly inaccurate...

    Thanks
    James
  • ArchiverArchiver Posts: 46,084
    edited 2004-01-26 15:10
    In a message dated 1/26/2004 9:25:11 AM Eastern Standard Time,
    ensignkim113@y... writes:


    > I'm using the SRF08 (SONAR) with my BS2P. On the example it says to
    > pull up the inputs from the SRF08 to the stamp by hooking them up to
    > the 5V power supply with some resistors. I'm just wondering, what
    > is the point of doing that? I wired it without the resistors and it
    > seems to be working fine.. Is the actaully a reason to pull up the
    > inputs? Does it have something to do with accuracy? Because the
    > results I get are fairly inaccurate...
    >

    The pull up resistors keep you from getting erroneous readings. You should
    be using them.

    Sid Weaver
    W4EKQ
    Port Richey, FL


    [noparse][[/noparse]Non-text portions of this message have been removed]
  • ArchiverArchiver Posts: 46,084
    edited 2004-01-26 15:10
    In a message dated 1/26/2004 9:25:15 AM Eastern Standard Time,
    ensignkim113@y... writes:
    Hi,

    I'm using the SRF08 (SONAR) with my BS2P. On the example it says to
    pull up the inputs from the SRF08 to the stamp by hooking them up to
    the 5V power supply with some resistors. I'm just wondering, what
    is the point of doing that? I wired it without the resistors and it
    seems to be working fine.. Is the actaully a reason to pull up the
    inputs? Does it have something to do with accuracy? Because the
    results I get are fairly inaccurate...

    Thanks
    James
    James:

    Usually a manufacturer recommends pull up or pull down resistors as a
    precaution to prevent inputs and outputs from going into an undefined state
    which can
    cause problems. Just like the inputs on a TTL or CMOS chip, the chip may
    perform flawlessly under many applications with out tying the inputs either high

    or low but next time you use that circuit, they very well may not. The same
    would be true with your situation, your circuit may work great now but tomorrow
    or next week, maybe not. Also, are there resistors elsewhere in the circuit
    that may in fact be pulling those inputs/outputs high anyway.

    Maybe this will help out.

    Randy Abernathy
    4626 Old Stilesboro Road
    Acworth, GA 30101
    Ph / Fax: 770-974-5295
    E-mail: cnc002@a...

    I[noparse][[/noparse]Non-text portions of this message have been removed]
  • ArchiverArchiver Posts: 46,084
    edited 2004-01-26 15:26
    Hi James,

    Pullups keep the pin from floating and being in an undefined logic
    level when no input is available, in this case it pulls up to +5V.
    There are also pull down resistors which, as you might guess, pull
    down a pin to 0V. Regards,

    -Dave

    --- In basicstamps@yahoogroups.com, "James Dang" <ensignkim113@y...>
    wrote:
    > Hi,
    >
    > I'm using the SRF08 (SONAR) with my BS2P. On the example it says
    to
    > pull up the inputs from the SRF08 to the stamp by hooking them up
    to
    > the 5V power supply with some resistors. I'm just wondering, what
    > is the point of doing that? I wired it without the resistors and
    it
    > seems to be working fine.. Is the actaully a reason to pull up the
    > inputs? Does it have something to do with accuracy? Because the
    > results I get are fairly inaccurate...
    >
    > Thanks
    > James
  • ArchiverArchiver Posts: 46,084
    edited 2004-01-26 15:29
    In a message dated 1/26/2004 9:25:11 AM Eastern Standard Time,
    ensignkim113@y... writes:


    > I'm using the SRF08 (SONAR) with my BS2P. On the example it says to
    > pull up the inputs from the SRF08 to the stamp by hooking them up to
    > the 5V power supply with some resistors. I'm just wondering, what
    > is the point of doing that? I wired it without the resistors and it
    > seems to be working fine.. Is the actaully a reason to pull up the
    > inputs? Does it have something to do with accuracy? Because the
    > results I get are fairly inaccurate...
    >

    You should also have a 270 ohm resistor in series with the IR detector pin 3.

    Sid Weaver
    W4EKQ
    Port Richey, FL


    [noparse][[/noparse]Non-text portions of this message have been removed]
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