MMA845x (GY-45) and NRF52-DK with I2C/TWI: HELP

[aldrinleal]

Hello. Complete n00b here!

I've built a small sample on mbed of an I2c Scanner. Also tried other runtimes. Somehow, its not working.

I'm using a GY-45 Module, which wraps MMA8541 on it:

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By looking, it seems that technically, its resistors are at 4k7, while in truth, I only measured 2k2 on the board, which is puzzling. I applied into a scope and got a few dumps:

Any ideas of what can I do?

Thank you

[Jørgen Holmefjord]

Hi,

Can you provide a more detailed description of what is not working than "Somehow, its not working"? Did you test the TWI scanner example from our SDK?

You have not included any information on what mbed version your are using, or how you configure TWI/I2C in your code. mbed include the TWI driver from our SDK, and use this for some of the I2C code. This driver will enable internal pullup resistor for both SCL and SDA, maybe this could explain the value you are seeing? The pullups should be between 11 and 16 kohm, with a typical value of 13k.

[aldrinleal]

Hi Jørgen,

I tried both on mbed as well as TWI_Scanner as well (NRF5 sdk version 12.3). On both cases, they report all addresses as available (which is a sign that its not working)

Question: Will both mbed and NRF5-sdk will enable the internal pullup?

[Jørgen Holmefjord]

Have you connected the GY-45 Module directly to an unmodified nRF52-DK/PCA10040 board? 

If you use the TWI driver in the SDK (used by TWI scanner example), the pullups will be enabled. If they are enabled in mbed depends on what version and API you are using. Most likely they are enabled, but to be sure, you need to follow the API back to the implementation in the GitHub repository I linked in my last post.