I decided to write my own example explaining how to set up the Arduino to go to sleep. You may be wondering why this would be necessary. It can be greatly beneficial when the project your making is battery powered. Putting the Arduino to sleep will lower the current draw and in turn will allow your project to have a longer run time before needing new batteries. It also can be very beneficial in a number of IOT projects where you don’t need the microcontroller or external devices to be running all of the time
For the starting example code, we will use two push buttons as well as two LEDs to show when the board is awake and when the interrupt button has been pressed. When the board is awake the LED connected to pin 13 will blink. Once the push button is pressed that is connected to pin 11 it will put the Arduino into sleep mode and the pin 13 LED will no longer blink. To wake the board, the button attached to pin 2 will need to be pressed. When this button is pressed the LED connected to pin 10 will light up to show the interrupt has been activated.
Starting Example Code
//These are the two libraries that are needed
#include <avr/interrupt.h>
#include <avr/sleep.h>
/* Here we set up our inputs and outputs. LEDs connected to pins 10 and 13 and pushbuttons attached to 2 and 12 */
int ledPin = 13;
int sleepPin = 12;
int interruptPin = 10;
int wakePin = 2;
//sleepStatus is set up to keep track of the button input on pin 12.
int sleepStatus = 0;
void setup()
{
pinMode(ledPin, OUTPUT);
pinMode(interruptPin, OUTPUT);
pinMode(sleepPin, INPUT_PULLUP);
pinMode(wakePin, INPUT_PULLUP);
/* Next we have to enable an interrupt.
The function is set up like this attachInterrupt(pin, function, triggerMode)
PIN – can be either a 0 to call out digital pin 2 or 1 to call out digital pin 3.
FUNCTION – This is the function that will be run while in the interrupt
TRIGGER MODE – this will be the mode of the interrupt pin.
It can be one the following:
LOW – a low level trigger
CHANGE – a change in level trigger
RISING – a rising edge trigger
FALLING – a falling edge trigger
The IDLE sleep mode is the only mode that can use CHANGE, RISING, and FALLING modes.*/
attachInterrupt(0, wakeUpNow, LOW);
}
void sleepNow()
{
//print message to serial monitor to let the user know board has gone to sleep
Serial.println("going to sleep");
//delay is added to allow user to get the full message on the serial monitor before going to sleep
delay(15);
//enables the sleep mode
sleep_enable();
// This is where we enable the interrupt, the reason it is done here is so that if the button is pressed accidently it doesn’t interrupt the running program.
attachInterrupt(0,wakeUpNow, LOW);
/* The next line is where we choose the sleep mode we want to use for this code. There are a few options to choose from, each with their own uses. For more information on the sleep modes, please review the Atmega8 datasheet at [http://ww1.microchip.com/downloads/en/DeviceDoc/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061A.pdf](http://ww1.microchip.com/downloads/en/DeviceDoc/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061A.pdf)
The 5 different options for sleep modes, they are listed below from least power savings to most power savings:
SLEEP_MODE_IDLE
SLEEP_MODE_ADC
SLEEP_MODE_PWR_SAVE
SLEEP_MODE_STANDBY
SLEEP_MODE_PWR_DOWN
For this sketch, we will be using the most power savings possible so we choose SLEEP_MODE_PWR_DOWN */
//sleep mode is set here
set_sleep_mode(SLEEP_MODE_PWR_DOWN);
//This is where the device is actually put to sleep
sleep_mode();
//Here is where the device begins to wake up.
//First thing that is done is to disable the sleep mode
sleep_disable();
//disables the interrupt on pin 2 so the wakeUpNow code will not be executed during normal run time
detachInterrupt(0);
//wait 1 second so the user can notice the LED signaling the interrupt
delay(1000);
digitalWrite (interruptPin, LOW);
}
void wakeUpNow() //This is the code that runs when the interrupt button is pressed and interrupts are enabled
{
digitalWrite(interruptPin, HIGH);
}
void loop()
{
// turns the LED on
digitalWrite(ledPin, HIGH);
// waits for a second
delay(1000);
// turns the LED off
digitalWrite(ledPin, LOW);
// waits for a second
delay(1000);
//This is where the sleep pin is read. It is only active when the LED is off.
sleepStatus = digitalRead(sleepPin);
//If button is pressed, device will run the sleepNow function
if (sleepStatus == LOW) {
sleepNow();
}
}Initial Code Wiring Diagram
Link to Scheme-It Schematic: https://www.digikey.com/schemeit/project/arduino-uno-7FSP1FG40120/
Adding a Real Time Clock to wake the Arduino
Next instead of using buttons to put the Arduino to sleep and waking it up, we will add a RTC to control this. I will be using part 1528-1598-ND from Adafruit for this project. The reason why I chose this RTC, is its built-in interrupt. I originally had a DS1307 breakout board, but I quickly learned that it doesn’t include the interrupt, so it will not work for this project. There are also a few libraries that I downloaded to make this project work. Below are links to where I downloaded the .zip library files.
Links to Libraries:
GitHub - PaulStoffregen/Time: Time library for Arduino - this is a timekeeping library for Arduino
GitHub - JChristensen/DS3232RTC: Arduino Library for Maxim Integrated DS3232 and DS3231 Real-Time Clocks - this library is for the DS3231 and includes alarms which will be needed to wake the Arduino
Code for adding the RTC
#include <avr/interrupt.h>
#include <avr/sleep.h>
#include <DS3232RTC.h> // https://github.com/JChristensen/DS3232RTC this is the library for the DS2331 RTC
//RTC Module global variables
// Sets the wakeup interval in minutes
const int time_interval = 5;
// LED connected to digital pin 13
int ledPin = 13;
// active LOW, RTC will interrupt this pin momentarily to wake up
int wakePin = 2;
void setup() {
// set up the serial monitor
Serial.begin(9600);
//Set up the led pin as an output
pinMode(ledPin, OUTPUT);
//Set pin d2 to input using the built-in pullup resistor
pinMode(wakePin, INPUT_PULLUP);
//turning LED on
digitalWrite(ledPin, HIGH);
// These next few lines of code initialize the alarms to known values, clear the flags, and clear the alarm interrupt flags
RTC.setAlarm(ALM1_MATCH_DATE, 0, 0, 0, 1);
RTC.setAlarm(ALM2_MATCH_DATE, 0, 0, 0, 1);
RTC.alarm(ALARM_1);
RTC.alarm(ALARM_2);
RTC.alarmInterrupt(ALARM_1, false);
RTC.alarmInterrupt(ALARM_2, false);
RTC.squareWave(SQWAVE_NONE);
/* Uncomment this section to set the time on the RTC. Make sure to comment out after the first time
it is set or you will continue to reset the time everytime the sketch is uploaded. Also note that the clock is 24 hour format.
tmElements_t tm;
// the next few lines set the clock to the correct hour, minute, and second. Remember 24 hour format so 4pm = hour 16
tm.Hour = 8;
tm.Minute = 19;
tm.Second = 00;
// set the correct date on the RTC
tm.Day = 04;
tm.Month = 5;
tm.Year = 2019 - 1970; // in order to set the year correctly, just change the 2019 and leave the “- 1970” to get the correct offset
RTC.write(tm); // write the date and time to the RTC
*/
time_t t; //create a temporary time variable so we can set the time and read the time from the RTC
t = RTC.get(); //Gets the current time of the RTC
RTC.setAlarm(ALM1_MATCH_MINUTES , 0, minute(t) + time_interval, 0, 0); // Setting alarm 1 to go off in the amount of minutes that we have the time interval constant set to
RTC.alarm(ALARM_1); // clear the alarm flag
RTC.squareWave(SQWAVE_NONE); // configure the INT/SQW pin for "interrupt" operation (disable square wave output)
RTC.alarmInterrupt(ALARM_1, true); // enable interrupt output for Alarm 1
}
void loop() {
delay(5000);//wait 5 seconds before going to sleep. When in a project, we would it is best to make this short as possible
sleepNow(); // run the sleepNow function
}
void sleepNow() {
sleep_enable();//Enabling sleep mode
attachInterrupt(0, wakeUpNow, LOW);//attaching a interrupt to pin d2
set_sleep_mode(SLEEP_MODE_PWR_DOWN);//Setting the sleep mode, in our case full sleep
digitalWrite(ledPin, LOW); //turning LED off
time_t t;// creates temporary time variable
t = RTC.get(); //gets current time from RTC
Serial.println("Sleep Time: " + String(hour(t)) + ":" + String(minute(t)) + ":" + String(second(t))); //prints time stamp on serial monitor
delay(1000); //wait one second to allow the LED to be turned off before going to sleep
sleep_cpu();//heres where the Arduino is actually put to sleep
Serial.println("just woke up!");//next line of code executed after the interrupt
digitalWrite(ledPin, HIGH); //turns the LED on
t = RTC.get();//get the new time from the RTC
Serial.println("WakeUp Time: " + String(hour(t)) + ":" + String(minute(t)) + ":" + String(second(t))); //Prints time stamp
//Set New Alarm
int alarmTime = 0; //temporary variable to store the new alarm time in minutes
//the next few lines are to roll the alarm over when it gets near the next hour
if (minute(t) <= (60-time_interval))
{
alarmTime = minute(t) + time_interval;
}
else
{
alarmTime = (minute(t) + time_interval) - 60;
}
RTC.setAlarm(ALM1_MATCH_MINUTES , 0, alarmTime, 0, 0); // set new alarm
// The next few lines of code I use for troubleshooting. This way I can make sure the clock is waking up at the correct time
Serial.print("The next alarm will go off at: ");
//These lines are to print the correct hour that the next alarm will go off
if ((minute(t) <= 60-time_interval) && (hour(t) <= 22))
{
Serial.print(hour(t));
}
else if ((minute(t) >= 60-time_interval) && (hour(t) <= 22))
{
Serial.print(hour(t) + 1);
}
else
{
Serial.print(0);
}
Serial.print(":"); // print a colon symbol
//print the correct minute, including leading zero if less than 10
if (alarmTime <= 9)
{
Serial.print("0");
}
Serial.println(alarmTime);
//Last thing we do is clear the alarm flag
RTC.alarm(ALARM_1);
}
void wakeUpNow() //This is the code that happens when the interrupt is activated
{
Serial.println("Interrrupt Fired");//Print message to serial monitor
sleep_disable();//Disable sleep mode
detachInterrupt(0); //Removes the interrupt from pin 2;
}RTC Wiring Diagram
Link to Scheme it Diagram: https://www.digikey.com/schemeit/project/arduino-uno-rtc-sleep-TKBAG6G400UG/
Adding a Soil Moisture Sensor as well as a Temperature/Humidity sensor
To show you an example how this could be used, I decided to make a stand-alone plant monitoring system. To complete this I will use a soil moisture probe, 1568-1670-ND, as well as temperature/humidity sensor, 1528-1172-ND. What this program will now do is check the soil moisture content along with the temperature. I decided to leave out the humidity on this sketch but could be added back in with only a few lines of code.
This monitor system will then check to make sure the soil moisture is not too low. If it gets below a certain level of moisture content, it will activate a water pump or solenoid. In this example I am using a LED as an indicator in place of the water pump or solenoid.
For this sketch you will need to install the MPL115A2 library, which can be installed from the Manage Libraries Button, which is located under the Sketch Menu under Include Library or the zip file can be found here GitHub - adafruit/Adafruit_MPL115A2: Driver for the Adafruit MPL115A2 barometric pressure sensor breakout
Code for adding Temperature/ Humidity Sensor and Soil Moisture Sensor
#include <avr/interrupt.h>
#include <avr/sleep.h>
#include <DS3232RTC.h> // https://github.com/JChristensen/DS3232RTC this is the library for the DS2331 RTC
#include <Wire.h>
#include <Adafruit_MPL115A2.h>
Adafruit_MPL115A2 mpl115a2;
//RTC Module global variables
// Sets the wakeup interval in minutes
const int time_interval = 5;
// LED connected to digital pin 13
int ledPin = 13;
// active LOW, RTC will interrupt this pin momentarily to wake up
int wakePin = 2;
// LED connected to digital pin 10
int pumpLED = 10;
//variable for storing the soil moisture value
int moistureVal = 0;
//input for the moisture sensor
int soilPin = A0;
//pin used to power the soil moisture sensor
int soilPower = 7;
void setup() {
// set up the serial monitor
Serial.begin(9600);
//Set up the led pin as an output
pinMode(ledPin, OUTPUT);
//Set pin d2 to input using the built-in pullup resistor
pinMode(wakePin, INPUT_PULLUP);
//turning LED on
digitalWrite(ledPin, HIGH);
//Set D7 as an OUTPUT
pinMode(soilPower, OUTPUT);
// Set to LOW so no power is flowing through the sensor
digitalWrite(soilPower, LOW);
//Set D10 as an output
pinMode(pumpLED, OUTPUT);
//starting the temp/humidity sensor
mpl115a2.begin();
// These next few lines of code initialize the alarms to known values, clear the flags, and clear the alarm interrupt flags
RTC.setAlarm(ALM1_MATCH_DATE, 0, 0, 0, 1);
RTC.setAlarm(ALM2_MATCH_DATE, 0, 0, 0, 1);
RTC.alarm(ALARM_1);
RTC.alarm(ALARM_2);
RTC.alarmInterrupt(ALARM_1, false);
RTC.alarmInterrupt(ALARM_2, false);
RTC.squareWave(SQWAVE_NONE);
/* Uncomment this section to set the time on the RTC. Make sure to comment out after the first time
it is set or you will continue to reset the time everytime the sketch is uploaded. Also note that the clock is 24 hour format.
tmElements_t tm;
// the next few lines set the clock to the correct hour, minute, and second. Remember 24 hour format so 4pm = hour 16
tm.Hour = 8;
tm.Minute = 19;
tm.Second = 00;
// set the correct date on the RTC
tm.Day = 04;
tm.Month = 5;
tm.Year = 2019 - 1970; // in order to set the year correctly, just change the 2019 and leave the “- 1970” to get the correct offset
RTC.write(tm); // write the date and time to the RTC
*/
time_t t; //create a temporary time variable so we can set the time and read the time from the RTC
t = RTC.get(); //Gets the current time of the RTC
RTC.setAlarm(ALM1_MATCH_MINUTES , 0, minute(t) + time_interval, 0, 0); // Setting alarm 1 to go off in the amount of minutes that we have the time interval constant set to
RTC.alarm(ALARM_1); // clear the alarm flag
RTC.squareWave(SQWAVE_NONE); // configure the INT/SQW pin for "interrupt" operation (disable square wave output)
RTC.alarmInterrupt(ALARM_1, true); // enable interrupt output for Alarm 1
}
void loop() {
delay(5000);//wait 5 seconds before going to sleep. When in a project, we would it is best to make this short as possible
sleepNow(); // run the sleepNow function
}
void sleepNow() {
sleep_enable();//Enabling sleep mode
attachInterrupt(0, wakeUpNow, LOW);//attaching a interrupt to pin d2
set_sleep_mode(SLEEP_MODE_PWR_DOWN);//Setting the sleep mode, in our case full sleep
digitalWrite(ledPin, LOW); //turning LED off
time_t t;// creates temporary time variable
t = RTC.get(); //gets current time from RTC
Serial.println("Sleep Time: " + String(hour(t)) + ":" + String(minute(t)) + ":" + String(second(t))); //prints time stamp on serial monitor
delay(1000); //wait one second to allow the LED to be turned off before going to sleep
sleep_cpu();//heres where the Arduino is actually put to sleep
Serial.println("just woke up!");//next line of code executed after the interrupt
digitalWrite(ledPin, HIGH); //turns the LED on
t = RTC.get();//get the new time from the RTC
Serial.println("WakeUp Time: " + String(hour(t)) + ":" + String(minute(t)) + ":" + String(second(t))); //Prints time stamp
getTempAndSoil(); //Run the TempAndSoil function
//Set New Alarm
int alarmTime = 0; //temporary variable to store the new alarm time in minutes
//the next few lines are to roll the alarm over when it gets near the next hour
if (minute(t) <= (60-time_interval))
{
alarmTime = minute(t) + time_interval;
}
else
{
alarmTime = (minute(t) + time_interval) - 60;
}
RTC.setAlarm(ALM1_MATCH_MINUTES , 0, alarmTime, 0, 0); // set new alarm
// The next few lines of code I use for troubleshooting. This way I can make sure the clock is waking up at the correct time
Serial.print("The next alarm will go off at: ");
//These lines are to print the correct hour that the next alarm will go off
if ((minute(t) <= 60-time_interval) && (hour(t) <= 22))
{
Serial.print(hour(t));
}
else if ((minute(t) >= 60-time_interval) && (hour(t) <= 22))
{
Serial.print(hour(t) + 1);
}
else
{
Serial.print(0);
}
Serial.print(":"); // print a colon symbol
//print the correct minute, including leading zero if less than 10
if (alarmTime <= 9)
{
Serial.print("0");
}
Serial.println(alarmTime);
//Last thing we do is clear the alarm flag
RTC.alarm(ALARM_1);
}
void wakeUpNow() //This is the code that happens when the interrupt is activated
{
Serial.println("Interrrupt Fired");//Print message to serial monitor
sleep_disable();//Disable sleep mode
detachInterrupt(0); //Removes the interrupt from pin 2;
}
void getTempAndSoil()
{
float temperatureC = 0, tempF = 0; //set up float variable to store Celsius and Fahrenheit temp
temperatureC = mpl115a2.getTemperature(); //get temperature from the sensor
tempF = (temperatureC * 1.8) + 32; //convert the temperature from Celsius to Fahrenheit.
Serial.print("Temp (*F): "); Serial.print(tempF, 1); Serial.println(" *F"); //Print the temperature to the Serial Monitor
Serial.print("Soil Moisture = ");
//get soil moisture value from the function below and print it
Serial.println(readSoil());
addWater(); // Run the add water function
}
int readSoil()
{
digitalWrite(soilPower, HIGH);//turn the soil moisture sensor on
delay(10);//wait 10 milliseconds
moistureVal = analogRead(soilPin);//Read the value from sensor
digitalWrite(soilPower, LOW);//turn the soil moisture sensor off
return moistureVal;//send current moisture value
}
void addWater()
{
if (moistureVal <= 100) //If the soil moisture gets too low (The value will need to be set to accompany the soil that you are using)
{
//This is where you could change the code to run a relay, or run a water pump to water your plant. I just flashed a LED as an example to show that the plant would need to be watered.
for (int num = 0; num <= 10; num++)
{
digitalWrite(pumpLED, HIGH);
delay(1000);
digitalWrite(pumpLED, LOW);
delay(1000);
Serial.print("PUMP ON");
Serial.println(num);
}
}
}
RTC and Sensors Wiring Diagram
Link to Scheme it Diagram: https://www.digikey.com/schemeit/project/arduino-uno-rtc-and-sensors-sleep-0FCQKUG4006G/
Bill of Materials
Link to Cart: https://www.digikey.com/short/pj1hm1