Limitation of pull-up resistors on Qwiic bus

Qwiic System
1

I’m a bit confused about how many devices on a single Qwiic chain can have their pull-up resistors enabled.

The hookup guide for the Proximity Sensor says “If you have many devices on your I2C bus you may want to remove these jumpers. “ [Bold face is mine.]The Qwiic Micro OLED Hookup Guide says, “If multiple boards are connected on the same bus, make sure only one board has the pull-up resistors connected.”

Continually cutting traces, soldering, and desoldering slows up prototyping, so I’d like to avoid as much of that as possible. So, here are my questions?

  1. Is there a recognizable symptom that says, “Whoa! That’s too many .”?

  2. Would this work: Cut the PU-resistor traces on all but one low-power board and add it to the chain to provide the required resistors?

Thanks,

Bill

2

Hi Bill.

  1. Is there a recognizable symptom that says, “Whoa! That’s too many .”?
Generally, when everything stops working **or** you start having trouble with some Qwiic devices you know the resistance on the bus is too low. (Too many devices with pullups enabled.)
  1. Would this work: Cut the PU-resistor traces on all but one low-power board and add it to the chain to provide the required resistors?
That would be the preferred way to go as you only need one set of pullups on the bus. You can usually get away with two or three devices with pullups enabled but the more there are, the more likely you are to have trouble. Each device has to work harder to pull SCL or SDA back to ground when needed if the resistance is too low. Eventually, some devices won't be able to and then things stop working correctly.