I've nearly completed my project on M5Paper, with thanks to the people on this forum who've helped me over many hurdles. The crucial last aspect is to get it running as long as possible on battery.
Basically my project loads about 5 days worth of data from an internet resource; and then should update a display based on this data every 10 minutes or so.
My original intention (based on this line in the product description "battery life can be further preserved by using the RTC to set the device into deep sleep and wake it up again when needed") was that it could shut down completely, leaving the display intact; wake up every 10 minutes to update just a bit of the display; and every 4-5 days refresh the data feed.
However, it now appears that using the shutdown function with a time delay actually reboots the device when the time expires, rather than just waking up.
Q1: Is that correct, or have I missed an option that will to shut down everything except the RTC, but preserve state so that it doesn't reboot on wake up?
The second issue is that I don't want the display flashing every 10 minutes; it's an essential aspect of this project that the display should be discreet. Hence I only want to make small updates to the display every 10 minutes; larger updates every six hours or so.
From experiments, it's evident that the basic arduino 'delay' function makes little or no difference to power consumption.
I understand from the data on @felmue's info page and from this forum post that it should be possible to use either "light sleep" or "deep sleep". But (a) I've not been able to figure out the code for this and (b) I'm not clear from these sources whether I need to make a hardware modification before it is safe (and effective?) to use these functions. (I'm using an M5Paper V1.1.)
Q2: Is deep sleep my next best option to conserve power between updates, without causing massive screen blink?
Q3: Do I need to make a hardware modification in order to access this?
Finally, if I indeed I can get somewhere with the rest of this, I'm thinking that I'll do a completely shutdown for six hours or so in the middle of the night. That will probably mean reloading the data every 24 hours instead of every 4-5 days.
Q4: If I shut down the wifi immediately after loading data; is the power required to start up the wifi, find the access point, load the data etc more often significant? Or is the power draw of the device as a whole remain fairly steady regardless of whether the wifi is on? If I do shutdown every night, is it worth writing the data to SPIFFS so that it can recover it locally after rebooting, rather than getting it from the internet each time?
TIA for answers to any or all of these questions!