How to let your Arduino go to sleep and wake up on an external event. Preface Sleep is commonly used to save power on Arduino boards. For some Arduino variants, however, there is not much benefit. For example, the Arduino serial and USB boards use a 7805 type of power regulator, which needs 10mA when the Atmega IC is in idle mode. Putting these boards to sleep will cut a few mA off the total power consumption however it will still be high. If you bypass the inefficient regulator with your own power supply circuit, or use a board with a fairly efficient power supply, such as an Arduino Pro, then sleep can be very beneficial for reducing power and extending battery life. The regulator can even be removed altogether when using some Li-ion batteries.

Figure 1: a 220 Ohm resistor connects RX to pin 2 Global Principle Sleep is assisted by interrupts. Without them, only a reset can wake the Arduino up again. Fortunately interrupts are incorporated since the 0007 version of the Arduino IDE. On the hardware front, the Arduino is equipped with two interrupt ports: digital pin 2 and 3. So the Arduino can sense those pins for an event to wake up and resume execution of code.

Apr 25, 2010 Sleeping Arduino - Part 2 Wake Up Via An External Interrupt Overview. /* Setup the pin direction. */ pinMode(pin2, INPUT); Serial.println. Arduino Wake on LAN. The ENC28J60. MAC and upload it to Arduino using Arduino Studio. Open the Serial Monitor and set the. PinMode(buttonPin, INPUT); if. C Program Arduino Wake Up Light, raspberry pi wake up light, monochron clock kit, diy sunrise alarm clock, arduino alarm clock code, hf3470, ramp timer, arduino led. Sleep your Arduino to save power and wake on serial message.

It is even possible to execute special code depending on which pin triggered the wake up (the interrupt). Events on the USART (the serial port) will also wake up the Arduino.

In order for this to work, the Arduino must be in POWER_MODE_IDLE, the only power mode that doesn't disable the USART. Although this mode doesn't give great power savings you can use the functions provided in avr/power.h ( power_adc_disable(),power_spi_disable(),power_timer0_disable(), power_timer1_disable(),power_timer2_disable(),power_twi_disable()) to disable other hardware modules to achieve greater power savings. See for example code. When using SLEEP_MODE_IDLE, care must be taken to ensure that the 8-bit timer is disabled if you're using the arduino layer.

The timer can be disabled before entering sleep using the PRR = PRR 0b00100000; statement and subsequently re-enabled once out of sleep using PRR = PRR & 0b00000000;. The PRR refers to the Power Reduction Register. One must note that if this timer is disabled, the millis(); cannot be relied upon anymore if you need reliable data comparison before and after a sleep command. Because of the dominant way an interrupt breaks in in the execution of the main code, it is wise to make the code executed by an interrupt as short as possible. Maybe even just set a variable which will be handled in the main program. As long as the code for the interrupt runs, internal timers are waiting.

Level Interrupts When the arduino is in SLEEP_MODE_PWR_DOWN the only way to wake it is with either a watchdog timer interrupt, a level interrupt on pins 2 or 3, or a Pin Change interrupt (see ATmega328 datasheet Table 10-1, including note 3, on pg. A level interrupt means that the pin has to be held in that state for a certain amount of time before the interrupt is triggered. In the interrupt service routine (ISR) for a level interrupt, the interrupt must be detached otherwise the interrupt will keep happening and the ISR will be repeatedly called until the pin changes state. Example This code makes use of the Serial port to receive commands. In parallel to that it will count 10 seconds before going into sleep mode. The 220 Ohm resistor keeps pin 2 HIGH (because RX is internally pulled-up to 5V when used as Serial port) until there is serial information coming in. Note to the author: there is no need for a resistor between RX and pin 2 and the above statement is rather confusing. Download Dolphin Emulator Pro Alpha For Android.

In fact RX and pin 2 can be connected directly as RX is already connected to the output of the USB to serial converter and a serial line when in idle state is at logic HIGH (in TTL that means 5V). So pin 2 is effectively already pulled up at a HIGH state. A resistor may only be useful to limit contention between two outputs if one programs pin 2 as output by mistake (pins are input by default anyway), though current is already internally limited to 40mA. Note to the author #2: The attachInterrupt function is being called in the setup routine (line 68) and the sleepNow function (line 118). From the comments in the sleepNow function, I suspect that the call in the setup routine should be removed.