View raw code<\/a><\/p>\n\n\n\nHow the Code Works<\/h2>\n\n\n\n
In this example, the ESP32 is in deep sleep mode between each reading. In deep sleep mode, all your code should go in the setup()<\/span> function, because the ESP32 never reaches the loop()<\/span>.<\/p>\n\n\n\nImporting libraries<\/h3>\n\n\n\n
First, you import the needed libraries for the microSD card module:<\/p>\n\n\n\n
#include \"FS.h\"\n#include \"SD.h\"\n#include <SPI.h><\/code><\/pre>\n\n\n\nImport these libraries to work with the DS18B20 temperature sensor.<\/p>\n\n\n\n
#include <OneWire.h>\n#include <DallasTemperature.h><\/code><\/pre>\n\n\n\nThe following libraries allow you to request the date and time from an NTP server.<\/p>\n\n\n\n
#include <WiFi.h>\n#include <NTPClient.h>\n#include <WiFiUdp.h><\/code><\/pre>\n\n\n\nSetting deep sleep time<\/h3>\n\n\n\n
This example uses a conversion factor from microseconds to seconds, so that you can set the sleep time in the TIME_TO_SLEEP<\/span> variable in seconds.<\/p>\n\n\n\nIn this case, we’re setting the ESP32 to go to sleep for 10 minutes (600 seconds). If you want the ESP32 to sleep for a different period of time, you just need to enter the number of seconds for deep sleep in the TIME_TO_SLEEP<\/span> variable.<\/p>\n\n\n\n\/\/ Define deep sleep options\nuint64_t uS_TO_S_FACTOR = 1000000; \/\/ Conversion factor for micro seconds to seconds\n\/\/ Sleep for 10 minutes = 600 seconds\nuint64_t TIME_TO_SLEEP = 600;<\/code><\/pre>\n\n\n\nSetting your network credentials<\/h3>\n\n\n\n
Type your network credentials in the following variables, so that the ESP32 is able to connect to your local network.<\/p>\n\n\n\n
\/\/ Replace with your network credentials\nconst char* ssid = \"REPLACE_WITH_YOUR_SSID\";\nconst char* password = \"REPLACE_WITH_YOUR_PASSWORD\";<\/code><\/pre>\n\n\n\nInitializing sensors and variables<\/h3>\n\n\n\n
Next, define the microSD card SD pin. In this case, it is set to GPIO 5<\/span>.<\/p>\n\n\n\n#define SD_CS 5<\/code><\/pre>\n\n\n\nCreate a variable called readingID<\/span> to hold the reading ID. This is a way to get your readings organized. To save a variable value during deep sleep, we can save it in the RTC memory. To save data on the RTC memory, you just need to add RTC_DATA_ATTR<\/span> before the variable definition.<\/p>\n\n\n\n\/\/ Save reading number on RTC memory\nRTC_DATA_ATTR int readingID = 0;<\/code><\/pre>\n\n\n\nCreate a String variable to hold the data to be saved on the microSD card.<\/p>\n\n\n\n
String dataMessage;<\/code><\/pre>\n\n\n\nNext, create the instances needed for the temperature sensor. The temperature sensor is connected to GPIO 21<\/span>.<\/p>\n\n\n\n\/\/ Data wire is connected to ESP32 GPIO21\n#define ONE_WIRE_BUS 21\n\/\/ Setup a oneWire instance to communicate with a OneWire device\nOneWire oneWire(ONE_WIRE_BUS);\n\/\/ Pass our oneWire reference to Dallas Temperature sensor \nDallasTemperature sensors(&oneWire);<\/code><\/pre>\n\n\n\nThen, create a float variable to hold the temperature retrieved by the DS18B20 sensor.<\/p>\n\n\n\n
float temperature;<\/code><\/pre>\n\n\n\nThe following two lines define an NTPClient to request date and time from an NTP server.<\/p>\n\n\n\n
WiFiUDP ntpUDP;\nNTPClient timeClient(ntpUDP);<\/code><\/pre>\n\n\n\nThen, initialize String variables to save the date and time.<\/p>\n\n\n\n
String formattedDate;\nString dayStamp;\nString timeStamp;<\/code><\/pre>\n\n\n\nsetup()<\/h3>\n\n\n\n
When you use deep sleep with the ESP32, all the code should go inside the setup()<\/span> function, because the ESP32 never reaches the loop()<\/span>.<\/p>\n\n\n\nConnecting to Wi-Fi<\/h4>\n\n\n\n
The following snippet of code connects to the Wi-Fi network. You need to connect to wi-fi to request date and time from the NTP server.<\/p>\n\n\n\n
Serial.print(\"Connecting to \");\nSerial.println(ssid);\nWiFi.begin(ssid, password);\nwhile (WiFi.status() != WL_CONNECTED) {\n delay(500);\n Serial.print(\".\");\n}<\/code><\/pre>\n\n\n\nInitializing the NTP client<\/h4>\n\n\n\n
Next, initialize the NTP client to get date and time from an NTP server.<\/p>\n\n\n\n
timeClient.begin();<\/code><\/pre>\n\n\n\nYou can use the setTimeOffset(<time>)<\/span> method to adjust the time for your timezone.<\/p>\n\n\n\ntimeClient.setTimeOffset(3600);<\/code><\/pre>\n\n\n\nHere are some examples for different timezones:<\/p>\n\n\n\n
\n- GMT +1 = 3600<\/li>\n\n\n\n
- GMT +8 = 28800<\/li>\n\n\n\n
- GMT -1 = -3600<\/li>\n\n\n\n
- GMT 0 = 0<\/li>\n<\/ul>\n\n\n\n
Initializing the microSD card module<\/h3>\n\n\n\n
Then, initialize the microSD card. The following if<\/em> statements check if the microSD card is properly attached.<\/p>\n\n\n\nSD.begin(SD_CS); \nif(!SD.begin(SD_CS)) {\n Serial.println(\"Card Mount Failed\");\n return;\n}\nuint8_t cardType = SD.cardType();\nif(cardType == CARD_NONE) {\n Serial.println(\"No SD card attached\");\n return;\n}\nSerial.println(\"Initializing SD card...\");\nif (!SD.begin(SD_CS)) {\n Serial.println(\"ERROR - SD card initialization failed!\");\n return; \/\/ init failed\n}<\/code><\/pre>\n\n\n\nThen, try to open the data.txt<\/em> file on the microSD card.<\/p>\n\n\n\nFile file = SD.open(\"\/data.txt\");<\/code><\/pre>\n\n\n\nIf that file doesn\u2019t exist, we need to create it and write the heading for the .txt<\/em> file.<\/p>\n\n\n\nwriteFile(SD, \"\/data.txt\", \"Reading ID, Date, Hour, Temperature \\r\\n\");<\/code><\/pre>\n\n\n\nIf the file already exists, the code continues.<\/p>\n\n\n\n
else {\n Serial.println(\"File already exists\");\n}<\/code><\/pre>\n\n\n\nFinally, we close the file.<\/p>\n\n\n\n
file.close();<\/code><\/pre>\n\n\n\nEnable timer wake up<\/h4>\n\n\n\n
Then, you enable the timer wake up with the timer you’ve defined earlier in the TIME_TO_SLEEP<\/span> variable.<\/p>\n\n\n\nesp_sleep_enable_timer_wakeup(TIME_TO_SLEEP * uS_TO_S_FACTOR);<\/code><\/pre>\n\n\n\nInitializing the library for DS18B20<\/h4>\n\n\n\n
Next, you initialize the library for the DS18B20 temperature sensor.<\/p>\n\n\n\n
sensors.begin();<\/code><\/pre>\n\n\n\nGetting the readings and data logging<\/h4>\n\n\n\n
After having everything initialized, we can get the readings, timestamp, and log everything into the microSD card.<\/p>\n\n\n\n
To make the code easier to understand, we’ve created the following functions:<\/p>\n\n\n\n
\n- getReadings()<\/span>: reads the temperature from the DS18B20 temperature sensor;<\/li>\n\n\n\n
- getTimeStamp()<\/span>: gets date and time from the NTP server;<\/li>\n\n\n\n
- logSDcard()<\/span>: logs the preceding data to the microSD card.<\/li>\n<\/ul>\n\n\n\n
After completing these tasks, we increment the readingID<\/span>.<\/p>\n\n\n\nreadingID++;<\/code><\/pre>\n\n\n\nFinally, the ESP32 starts the deep sleep.<\/p>\n\n\n\n
esp_deep_sleep_start();<\/code><\/pre>\n\n\n\ngetReadings()<\/h3>\n\n\n\n
Let\u2019s take a look at the getReadings()<\/span> function. This function simply reads temperature from the DS18B20 temperature sensor.<\/p>\n\n\n\nsensors.requestTemperatures(); \ntemperature = sensors.getTempCByIndex(0); \/\/ Temperature in Celsius<\/code><\/pre>\n\n\n\nBy default, the code retrieves the temperature in Celsius degrees. You can uncomment the following line and comment the previous one to get temperature in Fahrenheit.<\/p>\n\n\n\n
\/\/temperature = sensors.getTempFByIndex(0); \/\/ Temperature in Fahrenheit<\/code><\/pre>\n\n\n\ngetTimeStamp()<\/h3>\n\n\n\n
The getTimeStamp()<\/span> function gets the date and time. These next lines ensure that we get a valid date and time:<\/p>\n\n\n\nwhile(!timeClient.update()) {\n timeClient.forceUpdate();\n}<\/code><\/pre>\n\n\n\nSometimes the NTPClient retrieves the year of 1970. To ensure that doesn\u2019t happen we force the update.<\/p>\n\n\n\n
Then, convert the date and time to a readable format with the getFormattedDate()<\/span> method:<\/p>\n\n\n\nformattedDate = timeClient.getFormattedDate();<\/code><\/pre>\n\n\n\nThe date and time are returned in this format:<\/p>\n\n\n\n
2018-04-30T<\/strong>16:00:13Z<\/strong><\/pre>\n\n\n\nSo, we need to split that string to get date and time separately. That\u2019s what we do here:<\/p>\n\n\n\n
\/\/ Extract date\nint splitT = formattedDate.indexOf(\"T\");\ndayStamp = formattedDate.substring(0, splitT);\nSerial.println(dayStamp);\n\/\/ Extract time\ntimeStamp = formattedDate.substring(splitT+1, formattedDate.length()-1);\nSerial.println(timeStamp);<\/code><\/pre>\n\n\n\nThe date is saved on the dayStamp<\/span> variable, and the time on the timeStamp<\/span> variable.<\/p>\n\n\n\nlogSDCard()<\/h3>\n\n\n\n
The logSDCard()<\/span> function concatenates all the information in the dataMessage<\/span> String variable. Each reading is separated by commas.<\/p>\n\n\n\ndataMessage = String(readingID) + \",\" + String(dayStamp) + \",\" + String(timeStamp) + \",\" + String(temperature) + \"\\r\\n\";<\/code><\/pre>\n\n\n\nNote:<\/strong> the “\\r\\n”<\/span> at the end of the dataMessage<\/span>variable ensures the next reading is written on the next line.<\/p>\n\n\n\nThen, with the following line, we write all the information to the data.txt<\/em> file in the microSD card.<\/p>\n\n\n\nappendFile(SD, \"\/data.txt\", dataMessage.c_str());<\/code><\/pre>\n\n\n\nNote:<\/strong> the appendFile()<\/span> function only accepts variables of type const char for the message. So, use the
![\"\"](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2018\/06\/ESP32-data-logging-thumbnail.jpg?resize=1200%2C675&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n![\"\"](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2018\/06\/ESP-32-data-logging-overview.png?resize=1040%2C704&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n![\"\"](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2018\/06\/esp32-datalogging-parts-required.jpg?resize=750%2C384&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n![](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2017\/10\/header-200.png?w=1200&quality=100&strip=all&ssl=1\")
<\/a><\/p>\n\n\n\n![\"\"](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2018\/06\/microsd-card-module.png?resize=750%2C455&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n![\"\"](\"https:\/\/i0.wp.com\/rntlab.com\/wp-content\/uploads\/2018\/05\/format-SD-card-1.png?w=1200&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n![\"\"](\"https:\/\/i0.wp.com\/rntlab.com\/wp-content\/uploads\/2018\/05\/format-SD-card-2.png?w=1200&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n![\"\"](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2018\/06\/esp32-data-logging_bb.png?resize=1200%2C565&quality=100&strip=all&ssl=1\")
<\/a><\/figure><\/div>\n\n\n![\"\"](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2018\/06\/esp32-data-logging-circuit.jpg?resize=750%2C421&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n![\"install](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2018\/06\/install-onewire-library-arduino-ide-2.png?resize=337%2C395&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n![\"Install](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2018\/06\/install-dallastemperature-library-arduino-ide-2.png?resize=326%2C422&quality=100&strip=all&ssl=1\")
<\/figure><\/div>\n\n\n