1.8V, Are You Serious?!?
what is made from FR4, is black+white in color, and supposedly makes beep-bloop-beep? the world’s smallest rollercoaster or known to be as KLST_PANDA.
yupp, last week has been a bit of a ride. after having completed the hardware test and being quite contempt with the results ( apart from the on-board microphone not working ) i connected the board again to the oscilloscope to test the audio quality and BOOOM! there it was. the audio signal was corrupted. it was chopped off below 0.3V! the problem was almost impossible to track down for a few days, especially since only two of the three produced boards showed this issue. one of them was performing perfectly fine. i tried literally everything to no avail, got really REALLY frustrated, doubted EVERYTHING, had to remind myself of what i am always preaching to the students ( “Develop Resilience to Frustration” ) and then as so often a lucky accident came to the rescue: while revisiting the audio codec’s datasheet ( for some other reason ) i saw somewhere mentioned ( casually as i might say ) on the side in the RECOMMENDED OPERATING CONDITIONS chart ( WM8904 datasheet p10 ) that parts of the power supply should only operate at levels up to 2.0V and typically at 1.8V ( i.e CPVDD, AVDD and DCVDD ) while the other two supplies are tolerant to up to 3.6V ( i.e MICVDD and DBVDD ) and typically operate at 2.5V respectively 1.8V. but 1.8V(!!!) are you serious … who, when, why?!? surely a classical case of RTFM slash datasheet but still 1.8V?!? this should be spelled out in blinking red burning letters on page 1. well, at least this potentially explains why the audio codecs misbehaved. still: i am mad!
KLST_CATERPILLAR
so after careful consideration and advice from more sane people, i designed a reduced version of KLST_PANDA which i called KLST_CATERPILLAR as in a weird wormlike lengthy being that eventually hangs itself from a branch to turn into an airborne beauty … which seems to fly into no particular direction in a bad frame rate but mostly ends up on a colorful and sweet flower, despite the fact that it was named after a clumsy mid-sized bear … ok metaphor deteriorates fast.