nRF52 Feather applying voltage to I2C pins

[jacobniman_gm]

Hello,

My current setup is a single Uno connected to 3 NRF52 modules through a 4 wire cable (pwr, gnd, scl, sda)

I've been having trouble establishing an I2C communication channel between the Uno and the feathers because when the feathers' I2C pins get connected to the Uno, the voltage difference narrows drastically. With only the Uno connected to a logic analyzer, the I2C pins read 4.7v high 0.5v low. Immediately when I plug in the feathers, it drops to 3.5v high 1.5v low which both the feathers and logic analyzer pick up as a permanent "high" state.

The issue is reproducible even with boiler plate example led blinking code on the uno and all feathers.

I wanted to know if there was anything known about this or if there are resistors / anything connected to the I2C bus on the Feathers that would be causing this issue

Thanks, ~Jake

[adafruit_support_carter]

The UNO is a 5V logic level board. The Feather NRF52 is a 3.3V logic level board. In general, you can not mix these two logic levels on the same I2C bus. You need to use something like this:
https://www.adafruit.com/product/757

[jacobniman_gm]

Continuing to use this thread because it has my setup information in on it,

I bought the component you recommended and attempted wiring it like so

HV - 5v power on the arduino
B3 - SDA on the arduino
B4 - SCL on the arduino
GND High- GND on the arduino
GND low- none (also tried gnd on the arduino, no change)
A4 - SCL for all three devices
A3 - SDA for all three devices
LV - 3.3v power on the arduino

the devices are powered straight from 5v on the arduino and direct ground. They power on fine but my analyzer says that A4 and A3 never change from 3.3v, even when B3 and B4 are changing to correct I2C signals

[adafruit_support_carter]

Try tying GND low to the GND of the 3.3V I2C devices.

[jacobniman_gm]

I resolved that problem (it was due to a faulty solder joint) but the board still doesn't properly resolve my issue. The feather side I2C is reading about 3.3v high right now but when the entire system is connected, the low voltage reading of both the arduino 5v and the feather 3.3v is 1.7v. Neither my logic analyzer nor the feathers are detecting this as I2C low.

I've attached a picture of the analyzer and it's voltage readings.

What steps should I take from here?

(It's worth noting that the i2c wine are approximately 2ft long, I'm not an expert but I attempted to research the max length of I2C wires and found that the generally considered max length is 1-1.5m so it shouldn't be an issue

[adafruit_support_carter]

It's worth noting that the i2c wine are approximately 2ft long

That's long-ish, but can be sometimes achieved if things are wired well. Post a photo of your setup showing all wiring connections.