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Doc
04-12-2007, 10:16 PM
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.

Chris Savage
04-12-2007, 11:13 PM
Doc,

ии 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

Doc
04-12-2007, 11:22 PM
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 Green
04-12-2007, 11:36 PM
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.