If you have a problem with your project (in this case you can't get the power consumption down to microamps) it's maybe a good idea to start with a bare minimum setup. In this case an Arduino Pro Mini, a regulated power supply and a sketch that's puts the Arduino to sleep. So for now you better focus on sleeping the Pro Mini and bring current consumption down to a couple of microamps before trying anything else.
First you need to understand what these power savings are all about. This site (Nick Gammon) is all you need to know about power saving techniques for microprocessors (a must read):
http://www.gammon.com.au/forum/?id=11497
Read it all, do some of the examples yourself and above all try to understand what's happening.
After that start with your basic setup to put the Arduino to sleep. This is how I do it:
Arduino Pro Mini: use the 3.3v version. Remove the power led because it's useless and it's still using a couple of milliamps. I lift it off the board by using a small watchmaker screwdriver. Try to get it between the bottom side of the led and the pcb and use some force to lift it from the board. You could also cut one of the connections from the led to the board. For now don't remove the voltage regulator (more about this later).
For the power supply I use a 3.3 volt LDO voltage regulator. In this case the HT7333-A (TO-92 package). I know there are a lot more LDO voltage regulators to choose from, but I have good results with this LDO. Search Ebay for it. Price is about $4 for 20 pieces. They have an ultra low quiescent current of only 4 microamps. According to the datasheet you need a 10 uF cap across Vin and GND and Vout and GND so use them. Find and read the datasheet to find out how to connect it.
Iām using 3 AAA batteries (alkaline) to power the voltage regulator. Later on you can try other options (step-up, step-down, other regulators and so on) but for now stick with the setup as described above.
Finally use the sketch below to put the Mini to sleep and check with your multimeter the current consumption. In this case I measured 38 uA with the voltage regulator in place (Voltcraft VC170 digital multimeter). After removing the voltage regulator I measured a current of only 3uA. Be aware that measuring very low currents are influenced by burden voltage (this is a nice video about burden voltage https://www.youtube.com/watch?v=fRP98k3Rh1E).
#include <avr/sleep.h>
void setup ()
{
// disable ADC
ADCSRA = 0;
set_sleep_mode (SLEEP_MODE_PWR_DOWN);
sleep_enable();
// turn off brown-out enable in software
MCUCR = bit (BODS) | bit (BODSE);
MCUCR = bit (BODS);
sleep_cpu (); // sleep within 3 clock cycles of above
} // end of setup
void loop () { }
Question is if it's really necessary to remove the voltage regulator to save an extra 35 uA. There is a nice battery life calculator here: http://oregonembedded.com/batterycalc.htm that will show you the difference in battery life when using 3uA or 38uA. I think a minimum period of 1 year before you have to replace/recharge your batteries is acceptable. Suppose you're using 3 AAA alkaline batteries. Capacity rating is then 1200 mAh (capacity is automatically derated by 15% to account for some self discharge.) Current consumption (without the regulator) is 0.003 mA. Current consumption during wake is 25 mA and the number of wakeups per hour is 12 (for example you take a temperature measurement every 5 minutes). Durations of wake time is 50 ms. If you use these figures with the calculator, battery life is 16 years. If you change 0.003 mA into 0.038 mA battery life will be 2.7 years. So you have to ask yourself if removing the voltage regulator (with the risk of destroying your mini which happened to me more than once) is really necessary. In this case I think it's not.
If you really want to remove the regulator there are several ways to do this. Best way (at least for me) is first cutting the legs of the regulator with a very sharp scalpel. Be careful to cut only the legs and not the board beneath it. Then try to lift it from the board by using a needle nose pliers. Use minimal force! If you have to use too much force then try to cut the legs a little further.
So there you have it. First try to prove to yourself that it's possible to get current consumption for an Arduino Pro Mini down to a few microamps and only then continue your adventures in MySensors land! Hope this helps.