I2C resistors on sensor beakout boards

Using Arduino Sensors
#1

I've been working on a sensor module consisting of an Arduino Nano, which im using to power the peripherals, and the following sensors on its I2C bus:

SHT35 breakout board (MOD-1030) (10k pullups)
www.embeddedadventures.com/sht35_humidity_and_temperature_sensor_mod-1030.html

TSL2591 breakout board (logic level shifters + voltage regulator with 10k pullups on both sides)
www.adafruit.com/product/1980

As7262 breakout board (logic level shifters + voltage regulator with 10k pullups on both sides)
www.adafruit.com/product/3779

K30 C02 sensor (no resistors)

I want to know wheter I should remove the integrated10k resistors on the SHT35, TSL2591 and AS7262, as in my knowledge the i2c data lines, and thus the resistors are connected in paralele combined resulsting equivalent pullup resistance for SDA and SCL of 3.3k ohm. I am thinking about replacing all these resistors with two single pull up resistors (4.7k or 3.3k) this would also provide a much needed pullup for the K30.

Would this be good or should I leave the resistors on the module and not add any? I want is functining pull up resistors for all of the sensors. I am not able to accurately know the bus capacitance and thus not able to calculate the maximum pull up resistance value with the formulas from the Texas Instruments application report (http://www.ti.com/lit/an/slva689/slva689.pdf), I do however think a resistor in the 2.8 - 4.7K range should suffice.

I'm also wondering why both sides of the BSS138 logic level shifter of the TSL2591 and AS7262 are equipped with pull up resistors, why is this done? Does a pull up on one side of the shifter/regulator not pull up the voltage on the the other side?

#2

Standard I2C is 3mA/400pF max.

3mA on 5volt logic works out to 5/0.003 = ~1k66 (minimum combined pull up resistance)
So no problem to add some more pull up to the 3k3 you already have.
Leo..

#3

Thank you for your response Wawa.

I'm still wondering wheter the pull-up resistors of the Adafruit (TSL2591 and AS7262) and SHT35 modules form an equivalent paralel resistance. Only if this is the case the K30 would be fine connected directly to the parralel wiring that im using for all the sensors to connect SDA/SCL/5V.

I have added an limage below (beware, low quality) showing how I plan on connecting the modules to the Arduino Nano.

[Album] Sensor module i2c resistor paint schema

The image is not fully representative of the real situation the Adafruit modules have a second set of pull up resistors before logic level shifter. all pull-up resistors are 10k ohm.

#4

http://www.embeddedadventures.com/datasheets/MOD-1030_hw_v1_doc_v1.pdf

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Seems that these three all have normal 10k pull up resistors.
I don’t see why you can’t parallel the values (3k3).
Leo…

#5

Don't worry, it will work just fine with those sensors all connected at the same time. The multiple pull-up resistors just act as parallel resistors, and the lower overall resistance is no problem at all - probably even a good thing considering the high parasitic capacitance of all those pin connections and extra wiring.

#6