Reducing Arduino’s Power Consumption Part 2

In Part two, of this three part series, we will look at how to use the Power Reduction Register (PRR) to reduce power consumption by turning off parts of Arduino that are not being used. This series is for anybody using Arduino for a battery powered project where maximizing battery life is critical.

*************************Arduino Code***********************************
/* This Arduino Sketch is part of a tutorial on the ForceTronics YouTube Channel and demonstrates how to use the 
Power Reduction Registers (PRR). It is free and open for anybody to use at their own risk.
*/

#include <avr/power.h>
     
 /* Power Reduction Register (PRR) functions from avr/power.h library. 
 For every disable function there is an enable function
  power_adc_disable() or power_adc_enable()
  power_spi_disable() or power_spi_enable()
  power_timer0_disable() or power_timer0_enable()
  power_timer1_disable() or power_timer1_enable()
  power_timer2_disable() or power_timer2_enable()
  power_twi_disable() or power_twi_enable()
  power_all_enable() or power_all_disable()
  
  Note that for max power efficiency you should also disable the rest of the module for ADC and SPI
   SPCR = 0; //disable SPI
   ADCSRA = 0;  // disable ADC
  */

void setup() {
  delay(6000); //Delay to see normal power level first
  ADCSRA = 0;  // disable ADC by setting ADCSRA register to 0
  power_adc_disable(); //disable the clock to the ADC module
  delay(4000); //delay to see just ADC off power level
  SPCR = 0; //disable SPI by setting SPCR register to 0
  power_spi_disable(); //disable the clock to the SPI module
  delay(4000); //delay to see just ADC and SPI off power level
  power_all_disable();
}

void loop() {
  // put your main code here, to run repeatedly:
}

Reducing Arduino’s Power Consumption Part 1

In part 1 of this 3 part series we look at how to use Arduino's built-in sleep modes to drastically cut down on power consumption to help you build projects with longer battery life. In part 2 of this series we will look at how to use power reduction registers and in part three we will look at some other ways to wake an Arduino up from sleep mode.

<avr/sleep.h> library: http://www.nongnu.org/avr-libc/user-manual/group__avr__sleep.html

//**********************Arduino Code***********************************
/*
Example program for using sleep modes in Arduino. This example code was used in a sleep mode tutorial video on the ForceTronics YouTube Channel.
This code is open for anybody to use at their own risk

The 5 different modes are:
     *     SLEEP_MODE_IDLE         -the least power savings
     *     SLEEP_MODE_ADC
     *     SLEEP_MODE_PWR_SAVE
     *     SLEEP_MODE_STANDBY
     *     SLEEP_MODE_PWR_DOWN
These are the arguments used to set the sleep mode in the function set_sleep_mode()
     */
     
#include <avr/sleep.h>

int led = 13; //variable for pin that the LED is on
int count = 0; //variable to control how many times LED blinks before sleep

void setup() {
   sleep_enable(); //enable the sleep capability
   set_sleep_mode(SLEEP_MODE_PWR_DOWN); //set the type of sleep mode. Default is Idle
   pinMode(led, OUTPUT); //set up the LED pin to output
}

void loop() {
  
  if(count < 4) { //For first four loops blink the LED
    digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
    delay(900);               // wait 
    digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
    delay(900);       // wait 
    count++; //increment count
  }
  else { //after blinking LED setup interrupt and then go to sleep. Note that sleep will only happen once since it is disabled in ISR
    attachInterrupt(0, interruptFunction, HIGH); 
    sleep_cpu(); //enter sleep mode. Next code that will be executed is the ISR when interrupt wakes Arduino from sleep
    count = 0; //Set the count back to zero 
  }
   
}

//This is the function called when the interrupt occurs (pin 2 goes high)
//this is often referred to as the interrupt service routine or ISR
//This cannot take any input arguments or return anything
void interruptFunction() {
 detachInterrupt(0); //this function call will turn the interrupt off
 sleep_disable(); //Disable the sleep mode so even if call to sleep is executed again it will be ignored
}

How to Interrupt Your Arduino

In this video tutorial we will look at how to use interupts on the Arduino Uno, Arduino Pro Mini, and any Arduino using the Atmega 328. Interrupts allow you to react immediately to an external event versus trying to constantly check for it in the main loop. 

Arduino Code****************************************************************
/*
  Interrupt Example
  Demonstrates how to use interrupts. When a high level is detected at pin 2 interrupt occurs and blinks LED at pin 13

  This example code is in the public domain.
 */

// Pin 13 has an LED connected on most Arduino boards.
// give it a name:
int led = 13;
//create a variable for ISR, has to be volatile if used in interrupt
volatile int bLED = 0;

void setup() {
  //Create interrupt: 0 for pin 2 or 1 for pin 3, the name of the interrupt function or ISR, and condition to trigger interrupt 
  attachInterrupt(0, interruptFunction, HIGH); 
  pinMode(led, OUTPUT); //set up the LED pin to output
}

// the loop routine runs over and over again forever:
void loop() {
  
  if(bLED) { //if this statement becomes true then the interrupt occurred
    digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
    delay(300);               // wait 
    digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
    delay(300);               // wait 
  }
  /*
  noInterrupts(); //disables interrupts
  // critical, time-sensitive code here
  interrupts();//enables interrupts
  */
}

//This is the function called when the interrupt occurs (pin 2 goes high)
//this is often referred to as the interrupt service routine or ISR
//This cannot take any input arguments or return anything
void interruptFunction() {
 bLED = 1; //with this variable set to 1 the LED will blink
 //detachInterrupt(0); this function call will turn the interrupt off
}