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把低功耗做到极致

超过 80% 的 LoRa 终端将由电池供电，这样一来，低功耗将是一个核心的技术挑战，一旦电能耗尽设备将“罢工”，在某些场合电能意味着 LoRa 终端的寿命。

ArduinoLoRa+ 是锐米推出的低成本快速开发 LoRa 终端方案，它能达到行业第一的低功耗(1.4uA)，最大限度地延长电池续航能力。

下面，逐步解密 ArduinoLoRa+ 极限低功耗是如何实现的。

上传休眠代码

#include <avr/sleep.h>

void setup () 

{

  pinMode(LED_BUILTIN, OUTPUT);

  int  count;

  for (count = 0; count < 5; ++count)

  {

    digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)

    delay(200);                       // wait for 200ms

    digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW

    delay(200);                       // wait for 200ms    

  }

  // disable ADC

  ADCSRA = 0;  

  set_sleep_mode (SLEEP_MODE_PWR_DOWN);  

  noInterrupts ();           // timed sequence follows

  sleep_enable();

  // turn off brown-out enable in software

  MCUCR = bit (BODS) | bit (BODSE);

  MCUCR = bit (BODS); 

  interrupts ();             // guarantees next instruction executed

  sleep_cpu ();              // sleep within 3 clock cycles of above

}  // end of setup

void loop () { }

LoRa 自动休眠

LoRa 开发板上电后闪烁 LED 共 5 次（表示正常工作），LoRa 模块入网后将自动休眠。将电流表串联在上述电路中，测量休眠电流为 1.4uA

唤醒技术

很明显，一个永久休眠的 ArduinoLoRa 平台是没有意义的，它需要被唤醒以从事某些工作，这可以通过“定时器”和“外部中断”来完成。请参考：

• ArduinoLoRa 休眠中断唤醒 1.4uA

• ArduinoLoRa 休眠定时器唤醒 5.5uA

• 编译和烧录下述休眠中断唤醒代码

• #include <avr/sleep.h>

•  

• /* 

•  * Example code to demonstrate the sleep functions in a Arduino.

•  *

•  * use a pull up resistor on pin 2 to 5V.

•  * and ground pin 2 momentary to wake it up again.

•  *

•  * When awake, the arduino will run the ledPin_blink code

•  */

•  

• const int ledPin = 13;  // ledPin connected to digital pin 13

• const int wakePin = 2;  // active LOW, ground this pin momentary to wake up

•  

• /* here we put the arduino to sleep */

• void sleepNow()

• {

• /* Now is the time to set the sleep mode. In the Atmega8 datasheet

•  * https://www.atmel.com/dyn/resources/prod_documents/doc2486.pdf on page 35

•  * there is a list of sleep modes which explains which clocks and

•  * wake up sources are available in which sleep modus.

•  *

•  * In the avr/sleep.h file, the call names of these sleep modus are to be found:

•  *

•  * 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     -the most power savings

•  *

•  * For now, we want as much power savings as possible,

•  * so we choose the according sleep modus: SLEEP_MODE_PWR_DOWN

•  *

• */  

•   set_sleep_mode(SLEEP_MODE_PWR_DOWN);  // sleep mode is set here

•  

•   sleep_enable();  // enables the sleep bit in the mcucr register so sleep is possible. just a safety pin

•  

• /* Now is time to enable a interrupt. we do it here so an

•  * accidentally pushed interrupt button doesn't interrupt

•  * our running program. if you want to be able to run

•  * interrupt code besides the sleep function, place it in

•  * setup() for example.

•  *

•  * In the function call attachInterrupt(A, B, C)

•  * A   can be either 0 or 1 for interrupts on pin 2 or 3.  

•  *

•  * B   Name of a function you want to execute at interrupt for A.

•  *

•  * C   Trigger mode of the interrupt pin. can be:

•  *             LOW        a low level triggers

•  *             CHANGE     a change in level triggers

•  *             RISING     a rising edge of a level triggers

•  *             FALLING    a falling edge of a level triggers

•  *

•  * In all but the IDLE sleep modes only LOW can be used.

• */

•   attachInterrupt(0, wakeUpNow, FALLING);  // use interrupt 0 (pin 2) and run function wakeUpNow when pin 2 gets LOW

•  

•   sleep_mode();  // here the device is actually put to sleep!!

• 
  

•   /* THE PROGRAM CONTINUES FROM HERE AFTER WAKING UP */

•   sleep_disable();  // first thing after waking from sleep: disable sleep...

•     

•   detachInterrupt(0);  // disables interrupt 0 on pin 2 so the wakeUpNow code will not be executed during normal running time.

• }

• 
  

• /* here the interrupt is handledPin after wakeup */

• void wakeUpNow()

• {

•   // execute code here after wake-up before returning to the loop() function

•   // timers and code using timers (serial.print and more...) will not work here.

• }

• 
  

• void flash()

• {

•   pinMode(ledPin, OUTPUT);

•   digitalWrite(ledPin, HIGH);

•   delay(50);

•   digitalWrite(ledPin, LOW);

•   delay(50);

•   pinMode(ledPin, INPUT);

• }

• 
  

• void setup()

• {

•   ADCSRA = 0;  // disable ADC

•   pinMode(wakePin, INPUT);

•   digitalWrite (wakePin, HIGH);  // enable pull-up

• }

•  

• void loop()

• {

•   flash();

•   sleepNow();

• }

• 硬件接线

• 如下图所示，使用杜邦线连接 LoRa 开发板和按钮，并使用电池供电。

• 

• 添加 Narcoleptic 低功耗定时器库

• 使用 Arduino IDE 打开工程，点击"Sketch -> Include Library -> Add .ZIP Library…"

• Narcoleptic 软件库 下载链接

• 
  

• 编译和烧录下述休眠定时器唤醒代码

• #include <Narcoleptic.h>

• 
  

• void setup () 

• {  

•   // disable ADC

•   ADCSRA = 0;  

• }  // end of setup

• 
  

• void loop () 

• { 

•   flash();

•   lowpwrDelay(4000); // During this time power consumption is minimised

• }

• 
  

• void flash()

• {

•   pinMode(LED_BUILTIN, OUTPUT);

•   

•   for (byte count = 0; count < 10; ++count)

•   {

•     digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)

•     delay(50);                       // wait for 50ms

•     digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW

•     delay(50);                       // wait for 50ms    

•   }

•   

•   pinMode(LED_BUILTIN, INPUT);

• }

• 
  

• void lowpwrDelay(long milliseconds)

• {

•   while(milliseconds > 0)

•   {

•     if(milliseconds > 8000)

•     {

•       milliseconds -= 8000;

•       Narcoleptic.delay(8000);

•     }

•     else

•     {

•       Narcoleptic.delay(milliseconds);

•       break;

•     }//if

•   }//while

• }

• 硬件接线

• 如下图所示，连接 LoRa 开发板和电池即可。

• 
  

•