I'm prototyping a ultra low power wireless sensor. To consume less I run a arduino mini pro at 1.8V at 8MHz with sleep 99% of time.
The power comes from a LIR2032 coin and the 1.8V is generated from a LDO regulator HT7318. I use the regulator cause my NRF24L01 will not support such as 4V voltage and cause an atmega328p consumes less with a lower voltage
I want the consumption be as low as possible (nA/pA if possible)
But to preserve battery life I have to know when voltage goes down.

I'm interested in the Nick scheme: enter image description here Measure Lithium ion battery voltage (thus remaining capacity)

But I got some trouble :
-A direct battery measurement is fully stable but drain battery.
-With Nick scheme it doesn't drain battery but I like to reduce the measurement time needed cause of the capacitor C14. (I added a capacitor to the arduino output to cut off the measurement a short time after switching)
-If I remove the capacitor from Nick scheme, the measurement is absolutely not stable, but I don't understand why ?

I read there are some all integrated solutions like LTC4150, are they better or worse considering ultra-low consumption?

Other links I found:
Low power battery voltage monitor
Zero or low-current voltage divider for switch identification
Which MOSFET to use for battery voltage measurement?
Reducing Voltage Divider Load to Extend Battery Life
Topic: Battery monitor/sensing ratio calculation on MotionMote/WeatherShield
Power saving techniques for microprocessors
Arduino Pro Mini: Power consumption

Sorry for my poor English :)

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    \$\begingroup\$ I want the consumption be as low as possible (nA/pA if possible) You should do a calculation using battery capacity, duty cycle of different modes to get the battery lifetime you want. If you achieve an average current below 1 uA that would already be very good. I advise you to make a spreadsheet for battery life calculation as that will tell you where the power goes (so what needs optimization). Unless you have a very low power LDO you will not benefit from using an LDO. An ATMega MCU can work on 1.8 V to 5.5 V, it does not need a constant 1.8 V. \$\endgroup\$ – Bimpelrekkie Dec 30 '17 at 14:13
  • \$\begingroup\$ Thank you for your answer <br>I use a LDO regulator cause my communication goes with a NRF24L01 ship which can survive with 4.2V and cause at 1.8V the atmega328P consums mutch less than at higher values <br><br> I read this: <br> [iot-experiments.com/arduino-pro-mini-power-consumption/] \$\endgroup\$ – ROUGEXIII Dec 30 '17 at 14:18
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    \$\begingroup\$ "Ultra low power ... arduino" Does not compute. \$\endgroup\$ – Olin Lathrop Dec 30 '17 at 14:23
  • \$\begingroup\$ Sorry I'm not familiar with stack-exchange answer system (no more editing possible after 5 minutes?), so I added my answer in the initial post to be more clear. \$\endgroup\$ – ROUGEXIII Dec 30 '17 at 14:30
  • \$\begingroup\$ @Olin maybe you think a MSP430 is better for this way? \$\endgroup\$ – ROUGEXIII Dec 30 '17 at 14:41

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