![\"Power](\"https:\/\/wolles-elektronikkiste.de\/wp-content\/uploads\/2020\/12\/Power_consumption_Boards-1024x257.png\")
<\/a>In this article, I am concentrating on the ATmega328P, as it is most common to those who work with the Arduino UNO. For many projects, however, it is oversized. That is why, at the end of the article, I will briefly handle the sleep modes of the less power-hungry ATtinys 85\/45\/25 using the example of the ATtiny85. The ATtinys 85\/45\/25 can also be programmed via the Arduino IDE. I described that here<\/a>. <\/p>\n\n I will not comment in the article, or very little, on how<\/em> the sketches are uploaded on the ATmega328P or the ATtiny85. I have described this in detail in the above-mentioned articles. It would be beyond the scope to repeat this in detail. <\/p>\n\n For orientation, the pinout scheme of the ATmega328P:<\/a><\/p>\n\n The Atmega328P offers six different sleep modes. Depending on the mode, more or less of its functions are sent to sleep. The remaining power consumption is correspondingly different.<\/p>\n If you send the ATmega328P to sleep, you must of course be able to wake it up again. Each mode has its selection of possible “wake-up calls”. In addition, it should be noted that the ATmega328P takes different times to wake up depending on the “sleep depth”. <\/p>\n The following table provides an overview of which sleep modes are still activated and how to wake up the ATmega328P again. The good news is that the table is valid for a whole series of ATmegas. <\/p>\n\n Here is a short description of Sleep Modes. More information can be found in the data sheet<\/a>.<\/p>\n The sleep modes are controlled by corresponding entries in the Sleep Mode Control Register SMCR. The Bits SM0… SM2 set the mode, the SE bit (sleep enable) starts sleep mode. <\/p>\n\n Not everyone likes to write into registers with instructions like To wake up, I use the watchdog timer, which I set to 8 seconds. Details about the watchdog timer can be found here<\/a>. I’ll discuss other wake-up methods later.<\/p>\n The sketch does the following:<\/p>\n \u00a0<\/p>\n \n\n For other Sleep Modes, simply uncomment the corresponding lines. Try idle mode. You will see that it is not working and the LED flashes with at a frequency of 3.5 s. Idle is a kind of light sleep and from such you wake up easily. We’ll come to see how you can prevent that. <\/p>\n\n And now try to swap lines 10 and 12. The LED now lights up while the ATmega328P is asleep, as all register contents are preserved during the sleep phase, including the port registers. <\/p>\n\n The function \n\n By the way, this is defined in sleep.h. You can find the file here: “Program Files (x86)\\Arduino\\hardware\\tools\\avr\\avr\\include\\avr\\sleep.h”. Don’t be sorry to look in. <\/p>\n It is safer if you use the more detailed command sequence and switch off all interrupts before But for now, the sketch looks like this:<\/p>\n<\/p>\n \u00a0<\/p>\n \n\n “Register fans” can replace lines 23 to 27 by:<\/p>\n<\/p>\n \n\n Less easy to read but nice in its brevity.<\/a> <\/p>\n\n I uploaded the last sketch on the Arduino UNO, the standalone ATmega328P and the ATtiny85, ran it using different clocks and measured the power consumption in the sleep phase. In some cases I uploaded the sketch using the Arduino IDE (as described in the last post), in the other cases I used Atmel (Microchip) Studio.<\/p>\n These values only apply to the conditions I have selected!<\/strong> Further measures (e.g. switching off the ADC) can achieve even more. <\/p>\n\n Some results were as expected, others not:<\/p>\n Depending on the sleep mode and the desired wake-up method, you can reduce power consumption even further by manually shutting off some components. This is controlled by the Power Reduction Register PRR:<\/p>\n\n Bits that are set switch off the corresponding component:<\/p>\n You don’t have to use binary operations to set the bits of your choice (although that’s not really hard). For this purpose, there are functions defined in the header file power.h. In the following sketch you will find the (self-explanatory) functions in lines 28 to 35.<\/p>\n To avoid fluctuating pin states during sleep, it is best to set the pins to OUTPUT\/LOW (line 6-11).<\/p>\n<\/p>\n \u00a0<\/p>\n<\/div>\n \n\n With this sketch I was able to reduce the current consumption at 5 V supply voltage to 6.3 \u00b5A<\/strong>. If I also switched off the watchdog, it went down to 0.28 \u00b5A<\/strong>. However, the ATmega328 then no longer wakes up at all. Alternatively, I tried a pin change interrupt as a wake-up method. This resulted in a current consumption of 0.71 \u00b5A<\/strong> – not too bad either. <\/p>\n As you can see, I have not used any of the options provided by the Power Reduction Register in this sketch. This was not necessary because the components were either not activated or were switched off in power-down mode anyway. The main additional saving compared to the previous sketch was switching off the ADC using If you are not sure what was activated in wake mode or not, it is better to switch off more than too little. However, you should not switch off anything that you need to wake up and you should not forget to switch the components back on again. <\/p>\n\n In case of a sudden, complete power failure, one speaks of a blackout. I think everyone knows this expression. A brown-out, on the other hand, is when the supply voltage of the microcontroller slips below a minimum level. Typically, this happens when the battery running your project drains. A microcontroller that gets too little voltage does completely unpredictable things. The microcontroller itself does not necessarily take any damage. But if the devices it controls do strange things, that might become critical. That’s why most microcontrollers have a Brown-Out Detector (BOD). This compares the operating voltage with a fixed trigger level. If this level is exceeded, a reset is triggered to protect the system. However, for some applications, a brownout may be unproblematic. <\/p>\n\n With the picoPower variants of the AVR microcontrollers, the Brown-Out detector can be switched off. You can recognize the picoPower models by the “P” in the name, e.g. the ATmega328P<\/strong>. The MCU Control Register MCUCR controlls the BOD:<\/p>\n\n The following bits are relevant:<\/p>\n Both bits must be set in a certain sequence to turn off the BOD. It is easier using the function Alternatively, if you use programs like Atmel Studio,<\/a> you can also control the BOD via the corresponding fuse bits (BODLEVEL). Settings 4.3 V, 2.7 V, 1.8 V, or “disabled” are available. <\/p>\n\n According to my measurements, turning off the BOD in the Sleep Mode Power-down saves another 8 \u00b5A of power. Doesn’t sound much, but in a year it’s about 70 mAh.<\/p>\n\n In continuous awake mode, lowering the clock frequency results in a considerable saving (see Table 1). However, you have seen that the power consumption of the microcontroller is frequency-independent, at least in power-down mode. If you send the microcontroller to sleep and only wake it up briefly from time to time to do a few things, it may be better to select a high clock frequency. The reason for this is that things are done faster at high clock speeds. The speed overcompensates for the higher power consumption. If you use delays, things are different again. There is an interesting discussion about this topic on mikrocontroller.net<\/a>. <\/p>\n\n A microcontroller acts like a capacitor or – more exact – like many small capacitors and their charge depends on the operating voltage. This is called parasitic capacities. In addition, there are leakage currents, e.g. from conductor track to another.<\/p>\n In power-down mode, I could reduce the power consumption of the ATmega328P from 0.15 mA (programmed via Arduino IDE) to 0.12 mA when I reduced the voltage from 5 to 3.3 volts. More information and comparative values can be found here<\/a>. <\/a><\/p>\n\n In previous examples, the watchdog was our alarm clock for the ATmega328P. I would now like to mention two other methods. <\/p>\n\n In the following sketch, the ATmega328P is awakened by external interrupts. For this purpose, I have attached a pushbutton to INT0 (PD2, Pin4 = Arduino Pin 2), which generates a HIGH signal when pressed. Each time the button is pressed, the ATmega328P wakes up, the LED lights up for 1 second, then the ATmega328P settles down again. <\/p>\n With the Arduino functions, the interrupt can be easily set up. It is advisable to deactivate the interrupt after waking up so that it is not triggered several times, for example due to bouncing of the pushbutton. I have used the short \u00a0<\/p>\n \n\n You can also write directly into the relevant registers, which is not really difficult. In the EICRA Register (External Interrupt Control Register A), you set the conditions for the interrupt.<\/p>\n\n In the EIMSK (External Interrupt Mask Register) the interrupt is activated:<\/p>\n\n Here’s what the sketch looks like: <\/p>\n<\/p>\n \u00a0<\/p>\n \n\n If you want to wake up the ATmega328P using a timer, you can do this with Timer2 in all sleep modes, except in power-down mode. Anyone who has read my posts about the 8-bit Timer0 and Timer2<\/a> and the 16-bit Timer1<\/a> knows that the Timer2 overflows in a relatively short time, even when using the maximum prescaler. I do not go into the details of the timer programming here again. <\/p>\n In the following example sketch, the Timer2 is set with the maximum prescaler. At a clock speed of 16 MHz, 16 mio\/1024\/256 = ~61 interrupts are triggered per second. To obtain an eight seconds rest phase, I added a counter that is incremented every time the MCU wakes up. Only after the 500th wake up the LED lights up. This equates to 500 \/ 61 = 8.2 seconds pause. One would think that waking up frequently leads to considerable surplus of power consumption. Surprisingly, I even found slightly less power consumption in the sleep phase compared to permanent sleep method using the watchdog timer (2.92 mA vs. 2.97 mA).<\/p>\n<\/p>\n \u00a0<\/p>\n \n\n Try and uncomment line 23. The ATmega328P then falls into a “sleeping beauty sleep” – but without a prince kissing it awake. Only a reset awakes it again.<\/a> <\/p>\n\n As mentioned at the beginning, the ATmega328P is not necessarily the first choice for an energy-saving project. With the knowledge acquired here, however, it should not be a problem for you to send other AVRs to sleep. Look at the data sheet and search for “sleep mode”. For example, the sleep mode table for the ATtiny85 \/ 45 \/ 25 looks like:<\/p>\n\n There are three sleep modes available, which can be activated via the corresponding functions from sleep.h. Awakening via the timer is not possible. However, if you write to the registers directly, you have to be aware that they have different names or that e.g. the watchdog timer has different prescalers. <\/p>\n\n This time I used a lot of pictures of Pixabay.<\/a> In detail, I would like to thank the hard-working photographers:<\/p>\n By using sleep modes and power management, valuable battery power can be saved on projects. I’ll show you how to control these features.<\/p>\n","protected":false},"author":1,"featured_media":8413,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[543],"tags":[556,1061,707,1088,1086,1081,1093,1094,1084,1091,1080,1082,1090],"class_list":["post-10152","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-boards-and-microcontrollers","tag-arduino-en-2","tag-atmega328p-en","tag-attiny85-en","tag-bod-en-2","tag-brown-out-en-2","tag-power-management-en","tag-power-down-en-2","tag-power-save-en","tag-power-h-en","tag-prr-en","tag-sleep-modes-en","tag-sleep-h-en","tag-smcr-en-2"],"yoast_head":"\nContent<\/h3>\n\n
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First of all….<\/h3>\n\n
Uploading the Sketches<\/h4>\n\n
Pinout of the ATmega328P<\/h4>\n\n
![\"\"](\"https:\/\/wolles-elektronikkiste.de\/wp-content\/uploads\/2019\/12\/Pinout-Atmega-328P-vs-Arduino-UNO-1024x495.png\")
<\/a>The sleep modes of the ATmega328P<\/h2>\n\n
![\"\"](\"https:\/\/wolles-elektronikkiste.de\/wp-content\/uploads\/2020\/02\/ATMEGA328P-1024x345.jpg\")
<\/a><\/figure>\n![\"\"](\"https:\/\/wolles-elektronikkiste.de\/wp-content\/uploads\/2020\/02\/Sleep_Modes_and_Wake_up_Sources_48_88_168_328-1024x569.png\")
<\/a>\n
Activating sleep modes<\/h2>\n\n
Control sleep modes via the SMCR<\/h3>\n\n
![\"\"](\"https:\/\/wolles-elektronikkiste.de\/wp-content\/uploads\/2020\/02\/SMCR-1024x92.png\")
<\/a>![\"Setting](\"https:\/\/wolles-elektronikkiste.de\/wp-content\/uploads\/2020\/02\/Sleep_Mode_Select.png\")
<\/a>Sleep modes using sleep.h functions<\/h3>\n\n
The short-notation<\/h4>\n\n
SMCR |= (1<<SM0);<\/code>. If you include the header file sleep.h, you can use less cryptic functions. How to do this, I show in the following sketch.<\/p>\n\n
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set_sleep_mode(...)<\/code>, in this case power-down<\/li>\nsleep_mode()<\/code> starts sleep mode<\/li>\nsleep_mode()<\/code><\/li>\n<\/ul>\n<\/p>\n#include <avr\/wdt.h>\n#include <avr\/sleep.h>\n\nvoid setup(){\n DDRD = (1<<PD7); \/\/ equals (roughly) pinMode(7, OUTPUT);\n watchdogSetup();\n}\n\nvoid loop(){\n PORTD |= (1<<PD7); \/\/ equals (roughly) digitalWrite(7, HIGH);\n delay(3500);\n PORTD &= ~(1<<PD7); \/\/ equals (roughly) digitalWrite(7, LOW);\n delay(3500);\n wdt_reset();\n\n set_sleep_mode(SLEEP_MODE_PWR_DOWN); \/\/ choose power down mode\n\/\/ set_sleep_mode(SLEEP_MODE_PWR_SAVE); \/\/ choose power save mode\n\/\/ set_sleep_mode(SLEEP_MODE_STANDBY); \/\/ choose external standby power mode\n\/\/ set_sleep_mode(SLEEP_MODE_EXT_STANDBY); \/\/ choose external standby power mode\n\/\/ set_sleep_mode(SLEEP_MODE_IDLE); \/\/ did not work like this!\n\/\/ set_sleep_mode(SLEEP_MODE_ADC); \/\/ choose ADC noise reduction mode\n\/\/ sleep_bod_disable(); \/\/ optional brown-out detection switch off \n\n sleep_mode(); \/\/ sleep now!\n}\n\nvoid watchdogSetup(void){\n cli();\n wdt_reset();\n WDTCSR |= (1<<WDCE) | (1<<WDE);\n WDTCSR = (1<<WDIE) | (0<<WDE) | (1<<WDP3) | (1<<WDP0); \/\/ 8s \/ interrupt, no system reset\n sei();\n}\n\nISR(WDT_vect){\/\/put in additional code here\n}<\/pre>\nThe more detailed spelling<\/h4>\n\n
sleep_mode();<\/code> corresponds to the sequence of commands:<\/p>\n<\/p>\nsleep_enable(); \nsleep_cpu(); \nsleep_disable();<\/pre>\n
sleep_enable()<\/code> using cli()<\/code>. Before sleep_cpu()<\/code> you activate the interrupts again with sei()<\/code>. Without the intermittent shutdown, interrupts can “collide” with unpredictable consequences. This is particularly important when further commands are inserted between sleep_enable()<\/code> and sleep_cpu()<\/code>, and that is exactly what we will do soon. <\/p>\n#include <avr\/wdt.h>\n#include <avr\/sleep.h>\n\nvoid setup(){\n DDRD = (1<<PD7); \/\/ equals (roughly) pinMode(7, OUTPUT);\n watchdogSetup();\n}\n\nvoid loop(){\n PORTD |= (1<<PD7); \/\/ equals (roughly) digitalWrite(7, HIGH);\n delay(3500);\n PORTD &= ~(1<<PD7); \/\/ equals (roughly) digitalWrite(7, LOW);\n delay(3500);\n wdt_reset();\n\n set_sleep_mode(SLEEP_MODE_PWR_DOWN); \/\/ choose power down mode\n\/\/ set_sleep_mode(SLEEP_MODE_PWR_SAVE); \/\/ choose power save mode\n\/\/ set_sleep_mode(SLEEP_MODE_STANDBY); \/\/ choose external standby power mode\n\/\/ set_sleep_mode(SLEEP_MODE_EXT_STANDBY); \/\/ choose external standby power mode\n\/\/ set_sleep_mode(SLEEP_MODE_IDLE); \/\/ did not work!\n\/\/ set_sleep_mode(SLEEP_MODE_ADC); \/\/ choose ADC noise reduction mode\n\n cli(); \/\/ deactivate interrupts\n sleep_enable(); \/\/ sets the SE (sleep enable) bit\n sei(); \/\/ \n sleep_cpu(); \/\/ sleep now!!\n sleep_disable(); \/\/ deletes the SE bit\n}\n\nvoid watchdogSetup(void){\n cli();\n wdt_reset();\n WDTCSR |= (1<<WDCE) | (1<<WDE);\n WDTCSR = (1<<WDIE) | (0<<WDE) | (1<<WDP3) | (1<<WDP0); \/\/ 8s \/ interrupt, no system reset\n sei();\n}\n\nISR(WDT_vect){\/\/put in additional code here\n}<\/pre>\nSMCR |= (1<<SM1); \/\/ power down sleep mode\ncli();\nSMCR |= (1<<SE); \/\/ sleep_enable();\nsei();\nasm(\"SLEEP\"); \/\/ sleep_cpu();\nSMCR &= ~(1<<SE); \/\/ sleep_disable();<\/pre>\n
Benefits of the sleep modes – some measurements<\/h2>\n\n
![\"Power](\"https:\/\/wolles-elektronikkiste.de\/wp-content\/uploads\/2020\/12\/Power_consumption_Sleep_Modes-1024x446.png\")
<\/a>\n
Further energy-saving potentials<\/h2>\n\n
Saving energy with the Power Reduction Register<\/h3>\n\n
![\"\"](\"https:\/\/wolles-elektronikkiste.de\/wp-content\/uploads\/2020\/02\/PRR-1024x81.png\")
<\/a>\n
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#include <avr\/wdt.h>\n#include <avr\/sleep.h>\n#include <avr\/power.h>\n\nvoid setup(){\n DDRB = 0;\n DDRC = 0;\n DDRD = 0;\n PORTB = 0;\n PORTC = 0;\n PORTD = 0;\n\n watchdogSetup();\n}\n\nvoid loop(){\n delay(5000);\n ADCSRA = 0; \/\/ disable ADC\n set_sleep_mode(SLEEP_MODE_PWR_DOWN); \/\/ choose power down mode\n\/\/ set_sleep_mode(SLEEP_MODE_PWR_SAVE); \/\/ choose power save mode\n\/\/ set_sleep_mode(SLEEP_MODE_STANDBY); \/\/ choose external standby power mode\n\/\/ set_sleep_mode(SLEEP_MODE_EXT_STANDBY); \/\/ choose external standby power mode\n\/\/ set_sleep_mode(SLEEP_MODE_IDLE); \/\/ did not work!\n\/\/ set_sleep_mode(SLEEP_MODE_ADC); \/\/ choose ADC noise reduction mode\n\n cli(); \/\/ deactivate interrupts\n\n\/\/ power_usart0_disable();\n\/\/ power_spi_disable();\n\/\/ power_timer0_disable();\n\/\/ power_timer1_disable();\n\/\/ power_timer2_disable();\n\/\/ power_twi_disable();\n\/\/ power_adc_disable();\n\/\/ power_all_disable (); \/\/ short summary of the former six lines\n \n sleep_enable(); \/\/ sets the SE (sleep enable) bit\n sleep_bod_disable(); \/\/ disable brown-out detector\n \n \n sei(); \/\/ \n sleep_cpu(); \/\/ sleep now!! \/\/ no wake up option selected\n \n sleep_disable();\n power_all_enable();\n}\n\nvoid watchdogSetup(void){\n cli();\n wdt_reset();\n WDTCSR |= (1<<WDCE) | (1<<WDE);\n WDTCSR = (1<<WDIE) | (0<<WDE) | (1<<WDP3) | (1<<WDP0); \/\/ 8s \/ interrupt, no system reset\n sei();\n}\n\nISR(WDT_vect){\/\/put in additional code here\n}<\/pre>\nADCSRA = 0<\/code>. <\/p>\nTurning off the Brown-Out Detector (BOD)<\/h3>\n\n
What is a BOD?<\/h4>\n\n
How do I turn off the BOD?<\/h4>\n\n
![\"\"](\"https:\/\/wolles-elektronikkiste.de\/wp-content\/uploads\/2020\/02\/MCUCR-1024x79.png\")
<\/a>\n
sleep_bod_disable()<\/code> which is defined in sleep.h. In the last sketch (idle_mode_enable.ino) I had already inserted the function in line 33, but not yet explained and commented out. <\/p>\n![\"BOD](\"https:\/\/wolles-elektronikkiste.de\/wp-content\/uploads\/2020\/02\/bodlevel_fuses.png\")
<\/a>Lowering the clock frequency<\/h3>\n\n
Lowering the operating voltage<\/h3>\n\n
Other wake-up methods<\/h2>\n\n
Waking up via external interrupt<\/h3>\n\n
Using Arduino functions<\/h4>\n\n
sleep_mode()<\/code> function here to draw attention to the relevant things. <\/p>\n<\/p>\n#include <avr\/sleep.h>\n\nvoid setup(){\n DDRD = (1<<PD7); \n}\n\nvoid loop(){\n PORTD |= (1<<PD7); \n delay(1000);\n PORTD &= ~(1<<PD7); \n attachInterrupt(digitalPinToInterrupt(2), intRoutine, RISING);\n \n set_sleep_mode(SLEEP_MODE_PWR_DOWN); \/\/ choose power down mode\n sleep_mode(); \/\/ sleep now!\n}\n\nvoid intRoutine(){ \n detachInterrupt(2); \/\/ external interrupt disable (INT0)\n}<\/pre>\nProgramming in C<\/h4>\n\n
![\"\"](\"https:\/\/wolles-elektronikkiste.de\/wp-content\/uploads\/2020\/02\/EICRA-1024x77.png\")
<\/a>![\"\"](\"https:\/\/wolles-elektronikkiste.de\/wp-content\/uploads\/2020\/02\/INT0_Select-1024x219.png\")
<\/a>![\"\"](\"https:\/\/wolles-elektronikkiste.de\/wp-content\/uploads\/2020\/02\/EIMSK-1024x85.png\")
<\/a>#include <avr\/sleep.h>\n\nvoid setup(){\n DDRD = (1<<PD7); \n EICRA |= (1<<ISC01)|(1<<ISC00); \/\/ interrupt on rising edge of INT0\n}\n\nvoid loop(){\n PORTD |= (1<<PD7); \n delay(1000);\n PORTD &= ~(1<<PD7); \n EIMSK |= (1<<INT0); \/\/ external interrupt enable on INT0\n \n set_sleep_mode(SLEEP_MODE_PWR_DOWN); \/\/ choose power down mode\n sleep_mode(); \/\/ sleep now!\n}\n\n\/\/ INT0 interrupt service routine\nISR(INT0_vect){ \n EIMSK &= ~(1<<INT0); \/\/ external interrupt disable (INT0)\n}<\/pre>\nWake up by Timer2<\/h3>\n\n
#include <avr\/sleep.h>\n#include <avr\/power.h>\nint counter = 0;\n\nvoid setup(){\n DDRD = (1<<PD7); \n TCCR2A = 0x00; \/\/ Wave Form Generation Mode 0: Normal Mode, OC2A disconnected\n TCCR2B = (1<<CS22)|(1<<CS21)|(1<<CS20); \/\/ prescaler = 1024\n TIMSK2 = (1<<TOIE2);\n}\n\nvoid loop(){\n if(counter==500){\n TIMSK2 &= ~(1<<TOIE2);\n PORTD |= (1<<PD7); \n delay(1000);\n PORTD &= ~(1<<PD7); \n counter = 0;\n }\n TIMSK2 = (1<<TOIE2); \/\/ interrupt when TCNT2 is overflowed\n TCNT2 = 0;\n set_sleep_mode(SLEEP_MODE_PWR_SAVE); \/\/ choose power down mode\n \/\/power_timer2_disable(); \/\/ if you uncomment the MCU will sleep forever \n sleep_mode(); \/\/ sleep now!\n counter++;\n}\n\n\/\/ TIMER2 interrupt service routine\nISR(TIMER2_OVF_vect){ \n}<\/pre>\nApply sleep modes to other AVR MCUs<\/h2>\n\n
![\"\"](\"https:\/\/wolles-elektronikkiste.de\/wp-content\/uploads\/2020\/02\/Sleep_Modes_and_Wake_up_Sources_ATtiny_25_45_85-1024x428.png\")
<\/a>Acknowledgement<\/h2>\n\n
\n