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this post was submitted on 01 Feb 2024
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You will have a hard enough time just finding a SOC that you can get documentation for without signing and NDA and promising to buy massive quantities of them.
I thought of getting a low power arm cpu like the one in the raspberry pi zero 2 or something less powerfull and then use the rp2040 as a coprocessor. The rp2040 only uses a few ma so its a good choice and i could use interrupts to wake the main cpu. I can also put the rp2040 into sleep and only operate the screen and that would basically be a normal watch and it would last for months.
That's a lot to fit in a watch. The PCB layout will be difficult and the requirements for it will likely exceed what the usual prototype PCB manufacturers can produce.
The RP2040 is a power hog. It takes 180µA in its lowest power sleep mode. There are other microcontrollers that can be in run mode and use less power than a sleeping RP2040. I would suggest looking into some of the STM32L series microcontrollers. They can get down into the nanoamp range in sleep mode and run less than 100µA/MHz.
Thanks for the suggestion but of course ill look into what mcu i want better when it comes to that. A larger pcb at first doesnt bother me that much but i want to get down to watch size in the far-future. This is only a hobby project so nothings set in stone. Im also working on a flashlight right now so im balancing these two projects.