# Differential I2C Bus Extender (PCA9615) is making me cry

**URL:** <https://community.sparkfun.com/t/differential-i2c-bus-extender-pca9615-is-making-me-cry/36328>\
**Category:** Miscellaneous\
**Created:** [February 11, 2019, 11:46pm UTC](https://community.sparkfun.com/t/differential-i2c-bus-extender-pca9615-is-making-me-cry/36328 "2019-02-11T23:46:04Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![javiernicola](https://avatars.discourse-cdn.com/v4/letter/j/df788c/32.png) [@javiernicola](https://community.sparkfun.com/u/javiernicola)\
**Post date:** [February 11, 2019, 11:46pm UTC](https://community.sparkfun.com/t/differential-i2c-bus-extender-pca9615-is-making-me-cry/36328/1 "2019-02-11T23:46:04Z")

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Hola!

Im trying to set up a long i2c bus with 6 stm32 acting as slaves and 1stm32 acting as a master.

All of them connected to a differential i2c bus using Sparkfun´s PCA9615 board

[https://learn.sparkfun.com/tutorials/qw … okup-guide](https://learn.sparkfun.com/tutorials/qwiic-differential-i2c-bus-extender-pca9615-hookup-guide)

The master is asking for data from each slave, it works perfectly untill i connect 4 devices and everything goes silent.

![](https://cdn1.imggmi.com/uploads/2019/2/12/694eb49b3b96a181ee66db53711d92e7-full.png)[https://cdn1.imggmi.com/uploads/2019/2/ … 7-full.png](https://cdn1.imggmi.com/uploads/2019/2/12/694eb49b3b96a181ee66db53711d92e7-full.png)

I was expecting too much deformation or noise in the i2c signal but when i check the i2c signal received by the last slave6 i get this beautiful perfect signal.

On top the i2c communication failing with 6 slaves connected

On the bottom the i2c communication working good with 3 slaves connected

![](https://cdn1.imggmi.com/uploads/2019/2/12/a2a6230176ab829efead115286d03aaa-full.png)[https://cdn1.imggmi.com/uploads/2019/2/ … a-full.png](https://cdn1.imggmi.com/uploads/2019/2/12/a2a6230176ab829efead115286d03aaa-full.png)

What is happening?

They have different addresses

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**Author:** ![amongstmyselves](https://avatars.discourse-cdn.com/v4/letter/a/5f9b8f/32.png) [@amongstmyselves](https://community.sparkfun.com/u/amongstmyselves)\
**Post date:** [February 13, 2019, 12:18am UTC](https://community.sparkfun.com/t/differential-i2c-bus-extender-pca9615-is-making-me-cry/36328/2 "2019-02-13T00:18:08Z")

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If you’re using the Roger Clark based arduino core [https://github.com/rogerclarkmelbourne/Arduino\_STM32](https://github.com/rogerclarkmelbourne/Arduino_STM32) then make sure it’s up to date. I recently had some multiple processor issues with I2C which fixed this. My issue caused the STM32’s to freeze up.

Also if you’re using the onReceive function, I don’t believe the STM32 code has this implemented. Not 100% sure about this though. I know the older vesion of the core I was using doesn’t support it.

Steve.