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Linux capable chip with really low power consumption? (lemmy.zip)

submitted 5 months ago by [email protected] to c/[email protected]

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I want to build a linux(yes i want linux specifically or a deritive of it) smartwatch as a prototype that lasts ~24 hours. Ive been looking for chips that are small and power effient enough but most of them cant run linux. If i have a 400mah battery that gives me a power budget of about 60mw... I know its possibly because there are wearos(basically android) watches that last 3-4 days. I dont know what kind of sorcery that is but that means it consumes about 15mw??? I really do feel like im miscalculating something but i checked multiple times. Do they hibernate linux/android and run it off of another chip. I also dont know how to excecute that properly and its kind of off topic of my question. So point is linux on a ~60mw budget in s smartwatch. I want to use a mip display as i really like the look and it uses little power but if ever want a heart rate sensor in it thats even more power consumpotion. Thanks in advance i guess if a saint answers this shitstorm of a question.

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[–] [email protected] 1 points 5 months ago (1 children)

So basically its not possible for me with my little experience in embedded stuff and general tech savyness because its just so ridiculously well optimised and oiled? I could hack around and replicate some of it at least.

[–] [email protected] 4 points 5 months ago (1 children)

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.

[–] [email protected] 1 points 5 months ago (1 children)

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.

[–] [email protected] 4 points 5 months ago (1 children)

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.

[–] [email protected] 1 points 5 months ago

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.