SparkFun_QwiicBus

Qwiic System
1
  1. Why are resistors R1-R6 (100 Ohm and 390 Ohm) different from the recommended in the PCA9615 datasheet (120 Ohm and 600 Ohm)?
  2. At what speed on the I2C bus will the communication length by 100 feet (30 meters), as stated in the SparkFun advertisement? The PCA9615 datasheet says no more than 3 meters at a CLK=1 MHz.
    I2C
    I2C749×532 54.4 KB
2

1 - someone made a design decision and it worked when they tested it.

2 - give it a try and see what speeds work for your application.

3

  1. Usually, developers strictly apply the recommendations from the datasheets. If you set other resistances of resistors R1-R6, then there must be good reasons. For example, using a connecting cable with a wave resistance of not 100 Ohm, but 90 Ohm. But this should be written in the user manual, right?

  2. The cable length can be, for example, 300 meters, if you reduce the clock frequency, for example, to 1 kHz. Therefore, a person who buys a QwiicBus board expects a length of 30 meters at any clock frequency (including 1 MHz), which is incorrect.

4

I think you might be confusing hobby grade parts with commercial grade parts. Sparkfun carries hobby grade parts made for hobbyists, not commercial grade parts made for professionals.

For $12, it will either work for you or it won’t. If you’d like to spend $200, I’m sure you can get a part that’s guaranteed and has a ton of paperwork stating it will work under whatever conditions you specify and comes with a full users manual.

I’ve used these before and all I can say about them is they worked just fine over a random 100’ Ethernet cable I found laying around but your mileage may vary.

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