Analog ADT7420FBZ Question

Question

Hi all, I was just looking through the documentation for the ADT7420FBZ flex evaluation board here, and I have hit a bit of an issue.

Below is the wiring guide supplied by Analog:

Color	Reference Designator
Red	VCC
Black	Ground
White	SCL
Blue	SDA

From what I can see, this appears to be I2C, however I have hooked this up to a Raspberry Pi I have and tried to run i2cdetect, and it is not detected as a device. It's also clearly not SPI as there is no RX line on the temperature sensor.

Any ideas, great minds of element14?

Josh

shabaz · Accepted Answer

I see, in that case it may be a software issue. From memory, the RPI needs I2C enabled I think, i.e. using the raspi-config program, and then via the 'Advanced' menu option. I'm presuming you're plugging in just the small board, and not the full eval board? What I2C address are you writing to? I presume you're following the PDF datasheet pages 13-20 and particularly page 19, which has the read operation? If you are, then I think scope traces are needed to confirm that the RPI is sending out the correct signals : ( You could also confirm with any other I2C device, to check that your code can successfully talk to I2C devices. When you get to the register reading stage, from the datasheet page 19 it is clear that you need 'repeated start' capability - and I don't know which RPI libraries support this function (e.g. if you are using Python for example) - I've never done this on the RPI but I'm sure it has been done by others. Even without repeated start is is possible to successfully write to the device for now (of course the read capability is essential). I noticed a reference to the ADT7420 in this thread , so it may be worth posting a query on that forum in case anyone has example code to share, to save you time (saves reinventing the wheel). But I would definitely google for how to do I2C repeated start for the language you plan to use - for example, for C there is the linux/i2c-dev.h functions you could use, as long as the underlying hardware (i.e. the RPI BCM chip) supports it - I'm fairly sure it does, just I don't have enough experience with the RPI to know for sure, so I hope others can confirm.

Analog ADT7420FBZ Question

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