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BS2px with SRF235 — Parallax Forums

BS2px with SRF235

DocDoc Posts: 25
edited 2007-04-12 16:36 in BASIC Stamp
Hello,
I am using a SRF235 sonar with a bs2px microcontroller. I want to collect data in microseconds. Everything is allright but I have a stability problem. For a well defined distance, the output is not always the same. for example, I have a 1575 us +/- 5 us. I put 1.8k resistors on the SCL and SDA lines.
Does anyone have any idea please?!

Thank you.

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-04-12 16:13
    Doc,

    ·· As I’m not familiar with that SRF device I have no help to offer there, but regarding the connections…Do their specs call for 1.8K pull-ups? Those are awfully stiff pull-ups. Typically I2C uses 4.7K on both lines.

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    Chris Savage
    Parallax Tech Support
  • DocDoc Posts: 25
    edited 2007-04-12 16:22
    Hello Chris,

    thank you for your reply. Actually I tried them both, 1k8 Ohm and 4k7 Ohm, and I had the same problem, especially for distances larger than 15 cm.

    Regards,

    Doc
  • Mike GreenMike Green Posts: 23,101
    edited 2007-04-12 16:36
    Pullups on the SCL/SDA lines would not cause stability problems. You're not talking about a large difference here. I suspect this is inherent to the device and the measurement system. You're talking about differences on the order of 0.3%, probably not achievable with this device. Check with Devontech. They don't even mention this (resolution) on their datasheets.
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