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I have two Raspberry Pi's both model B revision 2, both running the most recent version of Arch Linux from NOOBS. I have tried my best to replicate the install procedure to get i2c working on both systems, but it is hard considering there is no official wiki post. Anyways, I can run

i2cdetect -y 1

on both of my Pi's, but only one will show the i2c device connected. The address of the sensor is 0x68, it is the MCP3422. Strangely, on the Pi that won't recognize the device, it shows an address as UU, but it is not the address of my device, and also it will not connect to WiFi when the sensor is attached. Unfortunately the Pi that isn't working is actually part of field research, so my debugging abilities are limited.

I would like know the best way to debug this issue with limited access to resources.

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The most likely reason for the I2C device not being seen is an incorrect connection.

I'd recheck the ground, power, and SDA/SCL connections you have made between the device and the Pi.

The UU suggests that the Pi's have different firmware revisions. I believe it is something to do with Wolfson I2S modules added to recent kernels.

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  • I appreciate the feedback but I checked the connections with a meter so I know that isn't an issue. As for the firmware, I am assuming the older Pi must have the older firmware, even though the Arch Linux versions are the same, do you know how to fix this?
    – camdenl
    May 15, 2014 at 8:28
  • uname -a on the Pi should give a string like Linux soft 3.12.19+ #682 PREEMPT... Use sudo rpi-update to update to the latest firmware. The UU is only displayed on bus 1. It doesn't seem to do any harm (I guess the address is reserved for Wolfson).
    – joan
    May 15, 2014 at 8:34
  • Firmware update via sudo pacman -Syu fixed the problem, thanks for your help.
    – camdenl
    May 16, 2014 at 14:10

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