What microcontroller can be taken to implement a wrist watch?

Question

Electronics

Those. worries about low consumption and compactness. For 27 I/Os (LEDs)

Answer 1

Nafig no need to cling all 27 LEDs to separate legs. Think about matrix inclusion.
It all depends on what functionality you want from the watch. If it's just a watch, Attiny 2313 is enough.

Answer 2

any because compared to the consumption of LEDs, any consumption of MK is minuscule.

Answer 3

In your case controller
Options:
EFM32 from Silabs (ex Energy Micro)
STM32L0/L1 from ST Microchip
has a lot of micro power controllers with RTC and 3V power supply. In any family - PIC16, PIC18, PIC24.
If the watch is LED, then use the accelerometer to turn on the indication when you wave your hand.