Wireless Temperature and Humidity Monitor With ESP8266





Introduction: Wireless Temperature and Humidity Monitor With ESP8266

The goal of this project is to make a temperature/humidity monitor that wirelessly logs the temperature and humidity to a remote server. We will use an Arduino Uno (or clone), a DHT11, an ESP8266, and ThingSpeak.com for this project. This is a great project to start using the ESP8266 for some basic data logging so let's get started!

Step 1: Gather Your Supplies

For this project I used an Arduino Uno clone but any Arduino board or clone will work.

Step 2: Create a ThingSpeak Channel

In order to log your temperature and humidity measurements online you need to have a website or webservice that can accept GET http commands. In this Instructable I am using ThingSpeak but there are other, similar services out there so feel free to use something else to log your data. To create a ThingSpeak account click here.

If you use ThingSpeak you will need to make a channel with two fields, one for temperature and one for humidity. They have a number of options for displaying data in graphs so I encourage you to explore these options and see what you like best. I settled on two simple line graphs with a 10 point average to smooth out occasional blips in the data. ThingSpeak will give you a Key for your channel that you will need to put into the code so that your channel will accept your data.

Step 3: Wiring

First we should cover some basics of the ESP8266 and the DHT11. Then we will move on to wiring them to the Uno.

The image above shows the front of the ESP8266 with the 8 broken out pins labeled. The ESP8266 runs at 3.3 V so make sure you connect the Vcc pin to the 3.3 V pin on the Uno. This also means that you will need to use a logic level shifter or make a voltage divider for the serial connection from the arduino board to the ESP8266 or you risk ruining it. If you don't want to buy a logic level shifter then you will need to make a voltage divider which you can do using two resistors. Sparkfun has a great tutorial on this so you can see how they build theirs and calculate which value resistors you will need to use. I used a 220 Ohm resistor and a 470 Ohm resistor for mine which got me close enough to 3.3 V. Since the ESP8266 outputs 3.3 V and the Arduino boards can take that voltage there is no need to do anything to the serial line from the ESP8266 to the Arduino.

The DHT11 spec is only +/- 5% humidity and 2 degrees Celsius so it is not a super accurate sensor. It's also only good for temperatures above freezing. The DHT22 is a bit more accurate so if that's important to you opt for it instead. Both sensors work with voltages between 3.3 - 5 V. The signal pin will need to be connected to a pull-up resistor, which I used a 4.7 kohm resistor for.

The Fritzing diagram above shows the wiring. For ease of use all connections to 5 V or 3.3 V are red and all connections to ground are blue. The wiring connections are as follows:

  • Uno | ESP8266
  • RXD | TXD
  • TXD | RXD (through voltage divider)
  • 3.3 V | Vcc, CH_PD, Reset
  • GND | GND
  • Uno | DHT11
  • 5 V | Vcc
  • GND | GND
  • D7 | Signal (connect to Vcc via pull-up resistor)

Step 4: Code

Before you can use my code you will need to download and install the DHT library from Adafruit. They have a description of how to install and use their library and a link to their GitHub repository. Their library comes with other features such as a heat index calculator which I don't show here but feel free to log that as well if you're interested in it!

The baud for the ESP8266 is set near the top of the .ino file. The version of the ESP8266 I bought comes in either 9600 baud or 115200 baud. Both of the chips I have ordered are set to 115200 baud but if you're trying to use this code and it doesn't seem to work try changing the baud to 9600 as your first step in debugging.

There are several places in code with values in '<' '>' brackets. Those are places where you will need to paste in your own values to make this work. This includes the name and password for your WiFi network and the Key for your ThingSpeak channel. There is code in place to use a red and green LED for debugging and status monitoring but those are not shown in the wiring diagrams. If you'd like to have a quick way to visibly see if things are running smoothly you can wire up a couple of LEDs.

A final thing that tripped me up for a while is that the serial pins CANNOT both be connected between the ESP8266 and the Uno while uploading the sketch. The sketch will fail to upload if they are connected so you must first disconnect one or both serial pins on either the Uno or the ESP8266 and then upload the sketch.

The code is attached to this step and can also be found on my GitHub page here.

Step 5: Use Your Sensor!

Congratulations, you've created your very own wireless temperature and humidity logger! I usually leave mine in my basement so that I can monitor the temperature, and more importantly, the humidity since it's unfinished and I don't want my things getting moldy from too much humidity. I have also mounted it to a piece of cardboard to make it easy to move around. I hope you found this helpful and had fun making it! In the future I plan to program the ESP8266 directly and bypass the Arduino altogether so look for that to come soon.

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How to convert fahrenheit to celsius?

Remove true from this line of code and you will get celsius.

float f = dht.readTemperature(true);

I first got only AT response. Nothing else. The I put 3 AA rechargeable batteries to feed power. That helped and now the system is working great! I changed the frequency to 600000 ms. Otherwise my phone freezes when trying to load Thingspeak charts and they are too heavy. I plan to get readings around my house to see if there is any risk with moist. Thank you so much!

hey i only get AT response too. where do u plug the AA battery? and can i use 3.3v power supply?


F:\TempHumidThingSpeak-master (1)\TempHumidThingSpeak-master\TempHumidThingSpeakPublic\TempHumidThingSpeakPublic.ino: In function 'void setup()':

F:\TempHumidThingSpeak-master (1)\TempHumidThingSpeak-master\TempHumidThingSpeakPublic\TempHumidThingSpeakPublic.ino:33:22: warning: deprecated conversion from string constant to 'char*' [-Wwrite-strings]



F:\TempHumidThingSpeak-master (1)\TempHumidThingSpeak-master\TempHumidThingSpeakPublic\TempHumidThingSpeakPublic.ino: In function 'bool updateTemp(String, String)':

F:\TempHumidThingSpeak-master (1)\TempHumidThingSpeak-master\TempHumidThingSpeakPublic\TempHumidThingSpeakPublic.ino:85:25: warning: deprecated conversion from string constant to 'char*' [-Wwrite-strings]



F:\TempHumidThingSpeak-master (1)\TempHumidThingSpeak-master\TempHumidThingSpeakPublic\TempHumidThingSpeakPublic.ino:104:21: warning: deprecated conversion from string constant to 'char*' [-Wwrite-strings]



F:\TempHumidThingSpeak-master (1)\TempHumidThingSpeak-master\TempHumidThingSpeakPublic\TempHumidThingSpeakPublic.ino:111:22: warning: deprecated conversion from string constant to 'char*' [-Wwrite-strings]



F:\TempHumidThingSpeak-master (1)\TempHumidThingSpeak-master\TempHumidThingSpeakPublic\TempHumidThingSpeakPublic.ino: In function 'boolean connectWiFi()':

F:\TempHumidThingSpeak-master (1)\TempHumidThingSpeak-master\TempHumidThingSpeakPublic\TempHumidThingSpeakPublic.ino:136:22: warning: deprecated conversion from string constant to 'char*' [-Wwrite-strings]



These look like compiler issues and look like they're only warnings so the program should still run and compile. Are you able to compile the code and upload it to the board still? I did some googling on that specific warning and it looks like an issue using strings instead of const char*. I didn't see these issues when I was using this though.


Thanks for the wonderful project

I am building this in a couple of day.
2 questions, Can be Also use BMP180 sensor and post its reading too ?

and I get error while compiling as

Arduino: 1.8.0 (Windows 7), Board: "Arduino/Genuino Uno"

temp-thing:23: error: 'DHT' does not name a type


I'll be most probably hooking up my Arduino Nano instead of UNO.

Hi ghpk, did you download and install the DHT library from Adafruit? It sounds like the library isn't being found. You can use any sensor you want for the temperature detection but you will need to either write the code to interface with it or find a library online. Good luck with this.

Thanks for this! Well done, but if its only about temperature I would definitely go with DS18B20 sensor because of the power consumption and no measurements delay. The DS18B20 consume less than 1 uA (~700nA) which is almost zero, and also gives the possibility to take advantage from PARASITE MODE and use only 2 wires instead of 3, by powering the sensor from the data line. From my experience DHT11 has a big downside in outdoors, can't resist in high moisture.

DS18B20 1 Wire temperature sensor

DHT22 Temperature and Humidty

ESP8266 Module tutorial