Arduino's super power-saving sleep mode has worked with one 18650 battery for 17 years

       Arduino The peripheral component modules of are very rich , I want to make a temperature alarm , But I found that battery power can't last for a few days , So I tossed for a period of time , Finally, the standby time is extended until I retire ^-^, Now let's share the process .
        First of all, we need to know the calculation formula of battery powered standby time . Usually the battery will be marked with a capacity of MAH (mAH).7 The capacity of No. 1 battery is 1.5V700mAH about . and 18650 The battery can easily do 3.7V3500mAH. If we choose 1 section 18650 3500mAH Battery for Arduino Work , How long can I stand by ？ hypothesis Arduino The average working current of is 30mA, that 3500/30=117 Hours =4.88 God , Obviously, it is far from our goal 17 The annual difference is too far . So if we want to achieve 17 The goal of annual standby , Then the current should be controlled at 3500/17 year /365 God /24 Hours =0.0235mA=23.5uA( To simplify the calculation , This paper does not consider battery self discharge 、 Voltage changes and temperature effects ).
        Okay , Had a target , Just try to control the standby current at 23.5uA Well ！

       1. The preferred 8Mhz Dominant Arduino The board , Because the vast majority of SCM programs are for 8M The main frequency is more than enough to run , but 8M Power consumption compared to 16M But it can be greatly reduced , You can personally test the power consumption under different working frequencies with frequency division code .
        2. The preferred 2.7V~5.5V Power Supply Board . because 18650 The battery voltage range is 2.7~4.2V, three links 7 Battery number is 3V~4.8V, To use up the battery , The single chip microcomputer must be able to work at the lowest 2.7V Stable operation under the voltage of .
        3. Simplify peripheral circuits , Mainly USB turn TTL circuit ,5V turn 3.3VLDEO Circuits, etc .
        Combine the three points above , Recommended direct use CC Nano Pro Development board , A treasure is on sale . This board has TYPE-C Interface pro Mini 8MHz 328P Chip development board , More importantly, it specially designed a peripheral circuit disconnection solder joint , After uploading the program, disconnect the solder joint LDO and USB circuit . Pictured

      4. The rest is code optimization , Go straight to the code , The idea is to let Arduino Boot into the SLEEP_MODE_PWR_DOWN Sleep mode , At this time, the measured current smoothly decreased to 23uA. Of course, nothing can be done , Open the watchdog interrupt , Wake up every second , Execute watchdog count . Wake up and enter loop loop , Then judge how many seconds have passed in the cycle , Perform the required functions as required .

#include <avr/sleep.h>
#include <avr/power.h>
#include <avr/wdt.h>

#define LED_PIN (13)

void OFFACDDC() {// close ACD and ADC
  ACSR |=_BV(ACD);
  ADCSRA=0;
  }

void ONACDDC() {// Turn on ACD and ADC
  ACSR &= ~_BV(ACIE);   
  ACSR &= ~_BV(ACD);   
  ADCSRA |= _BV(ADEN);   
  ADCSRA |= _BV(ADIF); 
  }

volatile int f_wdt = 1; // The watchdog counts 

ISR(WDT_vect) { // The watchdog wakes up the execution function 
  f_wdt++;
}

void enterSleep(void) { // put to sleep 
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  sleep_enable();
  sleep_mode();
  sleep_disable(); 
  power_all_enable();
}
void setup() {
   pinMode(LED_PIN , OUTPUT);
  digitalWrite(LED_PIN , LOW);
  OFFACDDC();
  
  /***  Set up a watchdog  ***/
  MCUSR &= ~(1 << WDRF); /*  Clear the reset flag . */
   WDTCSR |= (1 << WDCE) | (1 << WDE);
  //*  Set the new watchdog timeout  
  WDTCSR = 1<<WDP1 | 1<<WDP2;//  Every time 1 Second watchdog timeout 1 Time , You can also execute a post wake-up function  ISR
   WDTCSR |= _BV(WDIE);  /*   Set to timed interrupt instead of reset   */
}

void loop() {
  if (f_wdt >= 5) { // After waking up, it will run loop Of , At this time, check whether the wakeup reaches 5 Time , It's just 5 The second , A flash 
     ONACDDC();// Turn on ADC, So analog input IO Eloquence can be restored 
    digitalWrite(LED_PIN, HIGH);
    delay(20);
    digitalWrite(LED_PIN, LOW);
    f_wdt = 0;
     OFFACDDC();
  }
  enterSleep();// Keep sleeping 
}

    5. Practical application , For some simple low-power sensors, such as LM35, You can use numbers directly IO Mouth to mouth VCC Pin , In this way, you can wake up and use IO Mouth control LM35 Power supply , After work, the power supply was disconnected before hibernation . If it is WIFI Modules and other power consuming , A small power solid-state relay can be connected externally , Such as 211EH, It can also realize the requirement of power supply only after wakeup . In addition, the power consumption is reduced , In fact, you can add another 5V Small solar panels （ String several diodes , Ensure that the current does not flow back and does not exceed the maximum charging voltage of the battery under the strongest light ）, With rechargeable battery , Achieve unlimited endurance .

      PS:3 section 7 No. 2 battery is connected in series , stay 24uA It can work under current 700/0.024/24/365= 3.3 year .