I think @ScruffR’s note is pretty clear, but I just want to be double-sure I’m not in the middle of making some bad design decisions in a current project. I think I am.
The project uses the Argons/Xenons. On one Xenon we’re using the same Garmin Lidar Lite as the original poster with no pull-up resistors and a short (6") cable. It’s been working as expected, and this combination field-tested ok for several weeks of constant activity.
However, we are about to add 3 more sensor inputs to the same Xenon’s i2c bus using this i2c expander:
- In testing, I’ve been using the isolator board’s onboard pullup resistors. Based on ScruffR’s note, this is bad, correct? I should be using pullups from the Xenon’s sda/scl pins to 3.3v.
- Also I’ve been connecting the output of the board directly to the scl/sda pins on the Xenon. Sounds like this is also bad. Unlike 2nd gen devices, 3rd gen aren’t designed to tolerate 5v signals to the i2c pins. So even though this combination has been working in limited early testing, I’m asking for trouble longer term and should be using a 5v->3.3v level shifter. Correct?
So bottom line, 5v + i2c on 3rd gen = no-no?
TIA for any responses!