Published July 11, 2021 © GPL3+

Temperature and Humidity data logger (BT & SD)

Get temperature and humidity, log them to SD card and send live data to Bluetooth.

IntermediateFull instructions provided3,013

Temperature and Humidity data logger (BT & SD)

Things used in this project

Hardware components

Arduino UNO

Breadboard (generic)

Through Hole Resistor, 1 kohm

Through Hole Resistor, 2 kohm

Seeed Studio Grove - RTC

DHT11 Temperature & Humidity Sensor (3 pins)

HC-05 Bluetooth Module

Memory Socket, SD Card

Software apps and online services

Arduino IDE

Story

This prototype allows you to collect humidity and temperature data over time, save them to an SD card and send them live via Bluetooth.

In this project, I have been collecting temperature and humidity over night. All the info saved in the SD card were formatted in a way that they can be read as a CSV file. At the same time, the prototype was sending live data to a computer via Bluetooth, where the information was used for other purposes using Processing. The Processing software is still under review and I may or may not publish it at a later time.

The idea was to use this as a first step of a larger project where I monitor the temperature and humidity of a room and based on the values I would then program the Arduino to do something (eg. if the temperature goes above a certain lever, turn on or off a relay connected to an extraction fan or a servo motor that will open a window, etc.).

Due to the fact that the temperature and humidity were stable during the whole time, I may not continue with the second phase, however I kept the code as short as possible so that there is still room for other additions. You could also consider transferring some of the logic to the Processing program to free up some space on the Arduino and only use it for I/O. For instance, according to the info I was able to find, the SD card alone requires something like 40%+ of the total available memory. If you don't need to keep a written log on SD card and you are ok with just gathering all data from the computer through Bluetooth, this will free up space for the implementation of other services such as a servo motor, etc.

A few notes about the components:

1. In the schematics I have included a generic SD card module with the standard pinout, however, in the photo you will see I have actually used a micro SD card adapter converted into a micro SD module because I didn't have one available at that time. Feel free to use either a common SD card module or if you want to try and connect a micro SD card adapter just the way I did, check out these instructions on how to make one.

2. The RTC module I have been using is a DS1307. I wasn't able to find it within those available here in the Arduino Project Hub, however I have seen there are many similar ones available in the market (for example, this one).

3. The temperature and humidity sensor I have used is a DHT11 with 3 pins. Most of the ones in the market have 4 pins and the pinout is slightly different, but they are compatible and both can be used for this project with a little variation (I believe the 4th extra one is just another GND but you may want to check the pinout on Google to be sure before adding it to your project).

Code

Bluetooth & SD Temperature and Humidity logger

#include <SPI.h>
#include <SD.h>
#include <DHT.h>
#include <RTClib.h>
#define DHTPIN 2
#define DHTTYPE DHT11
DHT dht(DHTPIN, DHTTYPE);
const int chipSelect = 4; 
#include <SoftwareSerial.h>
SoftwareSerial SerialBT(9, 10);
File myFile;
RTC_DS1307 rtc;
void setup() {
  dht.begin();
  Serial.begin(9600);
  SerialBT.begin(9600);
  //SerialBT.println("Bluetooth connection is established");
  while(!Serial);
    if(! rtc.begin()) {
      Serial.println("Couldn't find RTC");
      while (1);
    }
    else {
      rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
    }
    if(! rtc.isrunning()) {
      Serial.println("RTC is NOT running!");
    }
  Serial.print("Initializing SD card...");
  if(!SD.begin(chipSelect)) {
    Serial.println("initialization failed!");
    return;
  }
  Serial.println("initialization done.");
  myFile=SD.open("DATA.txt", FILE_WRITE);
  if (myFile) {
    Serial.println("File opened ok");
    // print the headings for our data
    myFile.println("Date,Time,Temperature ºC,Humidity %");
  }
  myFile.close();
}
void loggingTime() {
  DateTime now = rtc.now();
  myFile = SD.open("DATA.txt", FILE_WRITE);
  if (myFile) {
    myFile.print(now.year(), DEC);
    myFile.print('/');
    myFile.print(now.month(), DEC);
    myFile.print('/');
    myFile.print(now.day(), DEC);
    myFile.print(',');
    myFile.print(now.hour(), DEC);
    myFile.print(':');
    myFile.print(now.minute(), DEC);
    myFile.print(':');
    myFile.print(now.second(), DEC);
    myFile.print(",");
  }
  myFile.close();
  delay(1000);  
}
void logging() {
  float t = dht.readTemperature();
    SerialBT.print(t);
    Serial.print(t);
    SerialBT.print(",");
    Serial.print(",");
  float h = dht.readHumidity(); 
    SerialBT.println(h);
    Serial.println(h);
  myFile = SD.open("DATA.txt", FILE_WRITE);
  if (myFile) {
    myFile.print(t);
    myFile.print(",");
    myFile.println(h);
  }
  myFile.close();
}
void loop() {
  //loggingTime();
  logging();
  delay(600000); // 600000 = 10 minutes
}

Credits

superturis

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Temperature and Humidity data logger (BT & SD)

Things used in this project

Hardware components

Software apps and online services

Story

Schematics

Breadboard

Schematics

Prototype

Data collected

Code

Bluetooth & SD Temperature and Humidity logger

Credits

superturis

Comments

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Temperature and Humidity data logger (BT & SD)

Temperature and Humidity data logger (BT & SD)

Things used in this project

Hardware components

Software apps and online services

Story

Schematics

Breadboard

Schematics

Prototype

Data collected

Code

Bluetooth & SD Temperature and Humidity logger

Credits

superturis

Comments

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