I have connected a pressure sensor to MKRFox1200, based on the following schematic, and powered them up using batteries. Pressure sensor output is 0.5 - 4.5 V and operating voltage of MKRFox 1200 is 3.3 V. So I used a voltage divider (two resistors) to scale down values coming from sensor. Each of the batteries are 4.5V - 4400 mAh and I connected them in series. Then I used LM7805C as a voltage regulator to have 5 V to feed MKRFox1200 through VIN pin. Pressure sensor is connected to 5v output of MKRFox1200.


Schematic:
<snip>

Pressure sensor datasheet:
<snip>

LM7805C datasheet (voltage regulator):
https://www.sparkfun.com/datasheets/Components/LM7805.pdf

MKRFox1200 page- specifications:
https://www.arduino.cc/en/Main.ArduinoBoardMKRFox1200


Now, I have following questions:

Considering following text from MKRFox 1200 page:
"Can run for over six months on 2 AA 1.5V batteries with typical usage.", and a typical Alkaline AA battery, has 2,500 mAh capacity.

1. How much would be power consumption of MKRFox1200? Is it P=3.3(v)*0.58(mA)= 1.9mW? (Current is found through: 2500mAh/4320 (hours in 6 months)= 0.58mA)
Are my calculations for this part correct?

2. In case my calculation from Question 1 are correct, then how it comes that the board can provide 7mA per pin as it is mentioned in MKRFox1200 page? I mean since it can draw only 0.58 mA from batteries, how can it provide 7mA per pin?
following image:
<snip>


3. How much is power consumption of whole the system?
I have calculated in this way, I don't know if it's right or wrong and why is wrong:
battery could drain 4400 mAh;
components current draw: MKRFox1200 = 0.58mA ; Sensor current draw = 1.4 mA ; Overal = 1.98 mA

4400/1.98 = 2222 h ( or 92 days)
Is it correct?
Shouldn't I consider their power (P=V.I) and efficiency of voltage regulator, based on the following figure?
<snip>



Possible question:
- Why pressure sensor is not connected directly to voltage regulator? - because it wasn't working in that case. I connected to 5v (vout) pin of MKRFox 1200 and it worked. Does it make any difference in power consumption?

Thanks in advance
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Edit: content edited on request of TS

 

Your batteries are drawn in parallel rather than series. Rather than a series of two resistors at the input if you want to divide it down as you are I would think about a 10K pot with a good temperature coefficient and adjust it so full scale pressure on your sensor gives you the desired 3.3 volts out, then scale your software to give the desired engineering units.

As to power consumption overall. Everything is approximate, for example if I am driving a bunch of DO lines (Digital Out) and each is drawing some current that current gets added to a total. The best way to get a feel for the actual current draw is measure it at the source, your batteries. Look at it under normal working conditions. Battery specifications are not always whet we expect. A 1.0 amp hour battery should deliver 1 amp for 1 hour before it has voltage drop but that is not the case, Looking at things that way a 10 mA draw should last 100 hours. The batteries should have a manufacturers chart with the curve which is not always a pretty linear curve. Also, the numbers are always for brand new fresh batteries, as they age they no longer meet those nice numbers.

Ron