Battery powered "sensor" node, mcu, step-up, LDO and many other choices - Page 1
Forum section: electronics / projects

author: nuclearcat
author_rank: Unknown
timestamp: May 20, 2020, 08:05:43 pm
content: Trying to find best design for "battery powered sensor nodes".Lot of choices have to be made.MCU - some generic, preferably ARM, but might consider MSP430 as well (do they worth it?). Only MCU that have opensource or free compilers.Sure minimal gentleman peripherals required, ADC, UART, SPI, I2C, reasonable flash/ram amount, and sure good price.One of the difficulties is that "3.3V default" lithium batteries are hard to find in my country. All I have is AA, AAA, and CR2032 (and some other other CR *).Question: Any suggestions for MCU?So:1)If i go with 3AA - it is inevitable loss on LDO with bypass (when voltage go below 3.3V), because i start with 4.5V+, then spend long time in 3.6V that is too close for absolute maximum for many chips.Question: is it true? I guess no way to avoid these losses, and i guess they are significant2)So if i go with 2AA, it means my voltage might go as low as 2V, then it's most likely i need something like TPS61040/TPS61041 for stable 3.3V, (28uA no-load and 1uA shutdown current i think is pretty good).Question: What is really better on your opinion? Thoughts? Anything better than TPS61040 available? (In some cases i might need to run ESP8266 comm module, i know its bad for batteries, so i will use it really rarely, but it means 150-200mA spikes).1 is seems really straightforward.But if i go 2, to keep it shut between data collection i need some timer. So options are:1)Fixed TPL5010, TPL5011 (perfect 35 nA current). It's $0.5 for fixed time wake up, can't say i'm very happy about that.Question: Is there any alternatives for TPL?2)Making some firmware for HT68F001/F002 (~2.5uA in IDLE mode), and using as flexible replacement of TPL.Question: Do you think it is good idea to use it for such purpose?3)Using some RTC chip with alarm function. (free timekeeping for some chip without RTC or powered off chip - as a bonus). Not sure about prices, will study this option more.4)Some MCU that can easily go to 2.0V on RTC domain, so i can keep powered VBAT directly from battery, and VCC from step-up.For now i consider as most feasible is STM32F/L.Sleeping on raw battery voltage, RTC domain only ON (it can handle until 2.0V on VBAT), with waking up over RTC and toggling PIN that will enable TPS6104* and supply to it stable 3.3V.As far as i know there is issues: it seems that STM32 cant toggle some PIN from RTC on alarm to enable step-up converter.Question: As it seems STM32F1 can't toggle some pin on RTC wake up, so on wake - MCU wont have VCC to actually wake...Can STM32L do this? Anybody aware about similar MCU that can do this?And sure maybe even directly going to something like nRF52(832?) that has all required, and even DC/DC onboard, and can run until 1.7V.It even contains the RF (i need it), but thats a problem too. I'm not sure that there are affordable (including for the price) modules with the recent revisions of the chip (their errata is nasty), and those modules circuitry is really "low power friendly".And i don’t think that i have enough experience and can make my own board for it, cheap and reliable (2.4Ghz!).Question:Did anybody used ready-made cheap nRF52 modules for battery powered application?And thank you for any advice in advance!