Sensebender Micro - Problem accessing accelerometer via SDA and SCL pins

[jwoods]

Has anyone had any issues using the SDA and SCL pins on the Sensebender Micro.

I have a sketch running on an Arduino Pro Mini ( 3.3v 8 Hz) that accesses a Sparkfun accelerometer via the SDA and SCL pins using a Sparkfun library. I’m able to upload this same sketch to the Sensebender Micro but when I run the sketch the accelerometer fails to initialize.

This same sketch runs perfectly on a Nano v3 and the Pro Mini. I’m trying to get the sketch working on the Sensebender Micro so that I can take advantage of the Micro’s low power consumption since I’m planning to run the Micro on AA batteries.

Thoughts?

Thanks

[mfalkvidd]

@jwoods this is just a wild guess, but maybe you need to add pullups to the signal lines? https://learn.sparkfun.com/tutorials/i2c/i2c-at-the-hardware-level

[tbowmo]

@mfalkvidd

There is two 4k7 pullups on the sensebender micro, as i2c is used for the onboard sensor.

@jwoods

One thought, can you use the onboard Si7021, while the accelerometer is attached to the sensebender? Also, which chip is used for the accelerometer? (Sparkfun has 3-4 different versions with different chipset onboard)

[jwoods]

@tbowmo - Thanks for the response. I'm using the mma8452q accelerometer. I'll have to pull some code together to see if I can get a reading from the si7021 while the accelerometer is attached.

[tbowmo]

@jwoods

You could just use the default sensebender micro sketch :)

just a thought, is there pullups on sda/scl on the Sparkfun board? If so, they are in parallel with the pullups on the sensebender, and when in parallel, the total resistance will be lower, and create a stronger pullup, which might mess up things.

[jwoods]

@tbowmo I’ve complied and uploaded the default sensebender micro sketch. The sketch hangs on the following line of code humiditySensor.begin(); -- actually hangs on Wire.endTransmission(); inside the begin procedure from the SI7021 library.

For my original sketch that accesses the accelerometer… that code also hangs when I call the a readRegister function that is also trying to execute Wire.endTransmission() function.

Could I have inadvertently damaged the sensebender and or the I2C circuitry?

[tbowmo]

It hangs without the accelerometer connected? Could sound like hw problems.

Do you have a scope so you coukd2check sda /scl lines?

[jwoods]

@tbowmo Correct. Hangs with and without accelerometer connected. No scope, only multimeter.

[jwoods]

@tbowmo - Just to close the loop on this one. A few weeks ago I had ordered a few additional Micro's.... they arrived today, uploaded my sketch and got good readings from the accelerometer. Must have been a problem with hw and or I2C circuitry. Thanks again for your assistance.

[tbowmo]

@jwoods

Thanks for the feedback :) problem could be either the atmega or the Si7021 chip on board the micro.. But hard to figure out without access to a scope..

(Btw. you have checked the board for solder bridges etc, right?)