The wake up pin directly trigger the enable pin of my voltage regulator (LM3671, 3.3V output), this chip drinks 10nA in off state.
Indeed, a 3.3V 8Mhz Pro Mini is as good as any.
So when setup and the PCF8523 timer expires or the alarm is activated the LM3671 goes off ?
PCF8523 timer doesn't expire, you have to reset the alarm flag by I2C, even if a second alarm comes during wakeup.For initial startup : PCF8523 start with a 32kHz square signal output on the output pin. I added a kind of low pass filter with a 10nF cap + 100k resistor.(And you also need a kind of not gate, as I didn't find a RTC with active high alarm, or too exensive, or something else wrong.)You have to detect that this is a first power up (with RTC registers), then setup everything on your RTC (including alarm), and last, disable 32kHz out. Blackout...Next alarm trigger, you detect that your RTC is setup correctly, do your measure, send it, and last, clear RTC alarm flag, Blackout.Even easier than having an additional MCU output to ensure regulator enable pin is high even if RTC doesn't do it.PS : wire that you see going up out of my screenshot is connected to a jumper, so that I can manually wakeup the system, for instance to setup via wifi/web page interface the system.