End-Point and Mid-Point Configuration

Qwiic System
1

Hi,

I have a long I2C network consisting of 2 end-points and a mid-point, the first stretch is about 13meters and the second around 2meters. This is connected to a RPi4 (via a Qwiic shim).

What I would like to do is utilise the green pair of the ethernet cable to send 12V to the end point, while also using the blue pair to power the PCA9165 at 5V (due to the long first section of cable).

Looking at the hookup guide this is “Alternate 3”, however I do not want to have the Qwiic bus on the last endpoint at 5V, as the sensors attached are not 5V tolerant - or at least the specs don’t say they are.

There are no sensors connected to the first endpoint, only the RPi. Also I am not to bothered if the buck regulator is powered or not.

Is it possible to maintain the 3.3V on the entire bus, when using the 5V and 12V as described?

As a side point/suggestion, if the VCC1 and the GRN through holes were swapped around a 5.08mm screw header could be used to supply the 5V/36V options.

Thanks in advance.

Darren.

2

https://cdn.sparkfun.com/assets/d/f/f/b … ematic.pdf shows the specifics of how the RJ-45 is wired internally, which should illustrate what you’re after

As for the 5v/3.3v problem, the easiest thing would be to just add in a logic level converter like these https://www.sparkfun.com/products/12009

3

Thanks for the link to the pdf, will come in useful!

As for the logic level converter, I would still need a 3.3V supply for the “low” side, which I won’t have (if I did I wouldn’t have this problem).

In the hookup guide there is this line:

“It is also strongly recommended to OPEN the 0-1 jumper on the primary / first EndPoint to isolate VCC (VDDA) from VCC1 (VDDB) but leave the 0-1 jumper on the terminating EndPoint CLOSED. Leaving the 0-1 jumper closed will send 5V to any Qwiic devices attached to your terminating / last EndPoint.”

Does this mean that if I open jumper 0-1 on the terminating endpoint it will stay at 3.3V?