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Fast I2C on HRO2
petiepooo Posted: 24 Sep 2023, 02:01 AM
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In the Hardware Reverse Oscilloscope 2 project writeup, you state "... to read it this quickly means fast i2c, and the pullup resistors on that breakout board weren't sufficient. I strengthened them by soldering extra resistors on top."

That's a little confusing, as strengthening implies increasing. In fact, you're decreasing the combined resistance by adding a parallel resistor such that the line level can change more rapidly. Stacking SMDs like that is a pretty clever way to do that. Was your goal to drop it from 10kΩ to 2.5kΩ by adding 3.3kΩ?

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mit Posted: 26 Sep 2023, 04:38 PM
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yeah whatever

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Yes, that's about right. I suppose the wording is a little ambiguous. Lower resistance means a stronger pull.

A similar ambiguity exists for mosfets and switches, about "open" and "closed". If you think of it as a switch, open implies open circuit and no current would flow. But if you think of it as a valve, open implies letting current through, and closing the valve would stop it. Often the ambiguity is quite hard to avoid!

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