Confused on voltage configuration options for Endpoint bus

Qwiic System
1

Hi all, hoping for some advice since I find the QwiicBus hookup guide quite confusing, especially if you’re not using a Midpoint.

I want to use two Endpoints to connect an Arduino Mega (DCC-EX command station) to a ESP-32 CAM about 3 meters away:

  • The Endpoint at the Arduino will be connected to a Qwiic connector on an EX-8874 motor shield. (supplies 3.3v; SDA & SCL at 5V).

  • I want to use the Green pair in the CAT5 cable to transmit 12v power sourced from a wall wart.

  • At the ESP-32 CAM end, a converter will step down the 12v to 5.2v to power the ESP-32 CAM (SDA & SCL at 3.3V).

    • Exactly how should the two Endpoints be configured (jumpers and power) to support this arrangement?

    Thanks much!

    2

    You’ll more-or-less need to go through the guide/options for your particular setup and mix-match instructions for one that doesn’t use a midpoint but matches your voltages profiles/wants…could be a bit tricky but you can always test/verify voltage and any changes made as you go with a multimeter

    3

    I think I understand it better now. In my opinion the Endpoint nomenclature makes matters more confusing - the PCA9615 uses VDDA and VDDB, but the Qwiic system refers to VCC and VCC1 (not to mention VCC2, which isn’t actually connected to anything other than the RJ45 jack).

    Right now I have both the chips and the bus powered at 3.3v, since I’m not sure whether the ESP32 I2C lines are 5v tolerant or not. My understanding from the data sheet is that the PCA9615 is 5V tolerant when powered at 3.3v, so the Qwiic system can be powered at 3.3v and interface with an Arduino Mega running at 5v. If the tolerance of the PCA9615 was mentioned in the hookup guide, I missed it.

    Which leads to a related question - how much current does a Qwiic bus need? I think the 3.3v regulator on the Arduino is rated at 150 mA, but I’m not sure what the current consumption of a PCA9615 network would be.