31 May 2018
Well, since the snippet about this project on the Hackday.com blog appeared I have received a lot of comments on the project, thank you all! I have also received the increased attention of AMS, and now have a lot more information about the use and status of the AS7265X system. In brief, the current board design, copied from the reference design in the data sheet (generation 1) is being changed to generation 2. The changes involve reassignment of the AS7262/3 slave reset pins and master AS72651 I2C bus pins. Furthermore, the changes are prompted partly because the I2C sector doesn't work in generation 1 with the current firmware. I2C in the AS7265X sensors is software based, so it depends on firmware alone (well, and the pin connections, of course). There is a new version of the firmware for generation 1 designs (like my current one) that is supposed to fix the I2C problem, but when I loaded it into my one assembled board I still couldn't get an I2C ACK from the AS72651 and AT mode works whether I2C_EN is HIGH or LOW.
So call the situation fluid.
This is understandable when bringing out a new chip set; bugs and typos are part of the package. And alpha users like me are both a blessing and a curse to companies like AMS. They benefit from having avid users point out early troubles and datasheet errors, etc, but the FAEs are busy and can't respond to every complaint. So far, AMS has been extremely generous with their time (thanks Frank!) and they have answered all of my questions as well as provided as much information as anyone could want. Kudos to AMS!
That said, this project is turning out to be quite a bit more challenging that the usual "copy-the-reference-schematic" design exercise.
I redesigned the board according to the generation 2 schematic and I have new generation 2 firmware ready to load when I get the boards back from OSH Park and assemble one of the boards. Maybe this time I will be able to get the I2C to work.
There are also going to be significant revisions in the data sheet with several I2C and AT commands deprecated and many more added. In particular, there will be registers for both raw data and calibrated data. Apparently, what I have been reading from my limited usage of the photospectrometer is the raw data. I am not sure yet what sort of calibration is involved here; the calibration coefficients, which are readable via I2C and UART, range from 1 to 17, so these are likely multipliers. But I don't know yet. More questions for AMS.
Bottom line, one step forward, two steps back, I need to get the photospectrometer working properly before I can explore any real world applications.