Hi everyone, we are currently trying to connect an external sensor to a Shimmer2R using the AnEx-Board. The sensor has a digital I2C-Interface and worked fine with a different microcontroller. However when connecting the sensor to the Shimmer, we ran into some electrical problems with the bus.
I used a modified version of the Boilerplate firmware, as it already contains I2C communication with the Mag sensor. However, I could not communicate with the external sensor. Using an oscilloscope, we found that the I2C requests are sent correctly to the sensor. When using a different I2C address (e.g. from the Mag) the external sensor does not respond (which is correct) and communication with the Mag also still works fine. When using the correct I2C address for the external sensor, it does try to send an ACK on the bus by pulling it low. However the bus does not completely go to GND (as it should), but instead goes to half VCC (1.5V) - which is totally wrong.... As this is an invalid bus level, the MSP does not read the ACK and communication is not possible. Could this be a problem of the pull-up? At the beginning we assumed we have to add our own pull-up and added a 4.7 k, but this does not seem to be necessary. It seems that Shimmer is using a 1.2 k internal Pull-Up, which is quite low but should be still OK. However I also could not find any documentation about this. Currently I have some theories: - The 1.2k pull-up is too small for the external sensor to pull the bus low. Could I remove this pull-up? - The connection wire to the external Sensor is too long (50cm) - We have some problems with proper GND or VCC on the external sensor board. - Using the 4.7k parallel to the internal pull-up we damaged either Shimmer or the Sensor. Any thoughts? Regards, Patrick -- --------------------------------------------------------- Dipl.-Inf. Patrick Kugler Researcher in the Digital Sports Group Pattern Recognition Lab Friedrich-Alexander University Erlangen-Nuremberg Martensstr. 3, 91058 Erlangen, Germany Room: Haberstr. 2, Room 01.006 Phone: +49 (0)9131 / 85-28980 E-Mail: [email protected] Web: www5.informatik.uni-erlangen.de/~kugler --------------------------------------------------------- This E-Mail (and any attachments) may contain confidential or personal information. Do not use, copy or disclose the content of this E-Mail without prior approval of the sender. _______________________________________________ Shimmer-users mailing list [email protected] https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users
