Yep DS3231 is the chip! I love that RTC. Expensive as all heck but no more than a minute deviation a year. No fussing around with IOT and time servers needed.
What clock project are you working on?
Like $2? I don't consider that too bad. Certainly worth the added cost over the crappy 1302/1307 RTCs!
The project is fundamentally a giant-digit alarm clock, something I can see without putting on my eyeglasses. With my eyesight, that means digits at least 3"/10cm tall for a clock at arm's length.
Of course, large digit clocks exist for sale, but other than big digits, they tend to be shit (bad user interfaces, etc). So I wanna make one that's beautifully designed in every other way, too!
Of course, the building is the main aspect, and it's a good way to put my spotty knowledge to the test -- it's been a great learning experience. (Some of the things I've needed to learn are: driving displays of various types, I2C and SPI, RTCs, buttons and matrices, and various aspects of coding*.)
I'm still not sure what kind of display I'm gonna use. I've been tinkering with a 64x32 RGB panel, but an Arduino struggles to drive it (it is 6,144 LEDs, after all!), and can't do high bit depths, the MCU just isn't fast enough. Another option is gigantic 7-segment LED displays (I finally found a source for white ones, all the way to 5"/12cm tall!). Making 7-segment displays out of WS8212B LED strips is another, which would allow full RGB without too much CPU load. I've even considered making 7-segments from LED filaments, though this is far harder to drive, since they're designed for 60+ volts. (The only firm requirement, aside from size, is that it not be a red LED display. I have an irrational hate of red LED displays.)
Obviously, a display that big, which is bright enough to be visible by day, would be insanely bright at night, so I'm gonna have to use ambient light sensing to adjust it for room light.
Recreating vintage display technology is of course also interesting. Aside from making mock-Panaplex displays with the LED filaments, two other fun approaches would be side-lit laser-etched plastic sheets with the segments, or projection displays.
Other pending items include: generating a pleasant alarm sound, maybe using a GPS or DCF receiver module to receive accurate time signals, perhaps a proximity sensor to wake up the display from dimmed by waving a hand nearby, and perhaps in the future interfacing with lighting projects.
* I'm a terrible programmer, and the coding has been the biggest challenge -- still pending are elegant button handling, and date operations. Real OSes have calendar libraries (with math functions, like adding/subtracting months/days/hours/mins) that handle things like leap years automatically, but I haven't found anything like that for Arduino, and I know that date handling is one of those "Here Be Dragons" minefields full of edge cases...