user:kluong:low_power_design_considerations [Smart Campus Energy Lab Wiki]

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Currently a draft:

**Low power design considerations**

I started this writeup after I was doing some reading about low-power arduino setups.

  * Previous designs are pretty inefficient - lets take a look at how inefficient, why and what we can do to design a better power system in the future. First we need to take a look at some of the constraints that we're dealing with:
    * Rooftop; no place to plug in
    * Hypothetical design consideration: raspberry pi - is it possible?
      * About 1A / 5V -> 5W
      * 6W solar panel charger not enough to charge during the day
      * 10W solar panel might be enough: https://www.adafruit.com/product/2747
      * Cost consideration
        * Driving down power consumption means cheaper solar panel and cheaper battery
  * The design choices are different for each hardware platform - this is not a critique on the designers / people 
    * Apple
    * Cranberry
    * Dragonfruit
    * Guava?
  * The assumption from before: we needed to either run things at 3.3v or 5v. Turns out we could run things at 2.8v - if we take a look at all of the modules, the one with the highest minimum voltage is the XBee at 2.8v. The atmega328p can technically run at a lower voltage.
  * Need to figure out this situation: if we run the mcu at 2.8v, can we still use the regular usb-serial converter? I think the logic lines will be fine.
  * XBee power states (sleep mode)
  * Microcontroller sleep modes
  * Sensors - how much power do they consume?
  * How low can we go? (Theoretical)


Footnotes:
  * 

Links:

  * http://www.home-automation-community.com/arduino-low-power-how-to-run-atmega328p-for-a-year-on-coin-cell-battery/
  * https://lowpowerlab.com/shop/index.php?_route_=Moteino/moteino-r4
  * https://www.rocketscream.com/blog/product/mini-ultra-8-mhz-arduino-compatible/
  * https://learn.sparkfun.com/tutorials/reducing-arduino-power-consumption/all



====== Example main ======

Using the low power library, here is what the loop function looks like:

<code>
    sleep_counter++;
    LowPower.idle(SLEEP_4S, ADC_OFF, TIMER2_OFF, TIMER1_OFF, TIMER0_OFF,
        SPI_OFF, USART0_OFF, TWI_OFF);
    if(sleep_counter % 15 == 0){
        board.sample(&board);
    }
</code>