How to Build Your Own ESP32 Temperature Monitor
By: Elizabeth Adams
Tags: DIY, Gadgets, Programming, IoT, Arduino

Things Used

Story

DHT22 Sensor, ESP32 Board

Temperature and environmental data is important in today’s industrial world. Monitoring data for server rooms, commercial freezers, and production lines is necessary to keep things running smoothly. There are lots of solutions out there ranging from basic to complex and it can seem overwhelming finding what your business needs and where to start.

In this post, I will walk through how to build a ESP32 temperature sensor system. The ESP32 combined with a DHT22 sensor will send temperature data to a data visualization tool. We have previously posted the comprehensive guide on streaming temperature with a Raspberry Pi and we received multiple requests for a similar tutorial using the ESP32. This temperature and humidity sensor has a temperature accuracy of +/- 0.5 C and a humidity range from 0 to 100 percent. It is simple to wire up and doesn’t require any pull up resistors.

ESP32 and Arduino IDE Setup

You’ll need to connect your ESP32 to your computer and run Arduino IDE to program it. You can start by downloading the Arduino IDE software to your computer. Once it is installed open it up and begin the process of adding your ESP32 board.

Go to Arduino > Preferences > Additional Boards Manager URL and enter the following in the box:

https://dl.espressif.com/dl/package_esp32_index.json

Next, go to Tools > Board > Board Manager…Search ESP32 and click install.

If you are using a Mac, you may need to install the Silicon Labs USB to UART Bridge VCP Driver to get the ESP32 to connect to your computer. Download the driver, install on your computer, and give it the necessary permissions to run.

In Arduino IDE go to Tools > Port and select “/dev/cu.SLAB_USBtoART”.

Initial State Account

We are going to use Initial State to send data from the ESP32. This will keep a historical log and allow you to view the real-time data. Go to https://iot.app.initialstate.com and create a new account or log into your existing account.

Once your account is set up, go to your settings to find your Initial State Access Key. This will be used later in the code. It will allow for data to be sent to your account.

Hardware Setup

The DHT22 will have three pins — 5V, Gnd, and data. There should be a pin label for power on the DHT22 (e.g. ‘+’ or ‘5V’). Connect this to 3V3 on the ESP32. The Gnd pin will be labeled ‘-’ or ‘Gnd’. Connect this to Gnd on the ESP32. The remaining pin on the DHT22 is the data pin and will be labeled ‘out’ or ‘s’ or ‘data’. Connect this to one of the GPIO pins on the ESP32 (I used 4, GPIO32). Once this is wired, power on your ESP32.

Software Libraries

You’ll need to install three libraries to use the sensor and send data to an IoT dashboard. Open the Arduino IDE, go to Sketch > Include Library > Manage Libraries…

Search for DHT Sensor Library, HTTPClient, and Adafruit Unified Sensor and install all three libraries.

Code

The code block below contains the full code for this project. I’ll walk through the different sections, what can be changed and what you need to know.

DHT Sensor

This part includes the DHT library, defines which pin to read data from, and sets the type of DHT sensor. If you are using a different GPIO from 4 you can change that here.

#include "DHT.h"

#define DHTPIN 4

#define DHTTYPE DHT22

DHT dht(DHTPIN, DHTTYPE);

User Settings

These are settings you need to add. For ssid put your WiFi name and for password put your WiFi password.

The accesskey and bucketkey are from your Initial State account. Your Initial State access key can be found in your settings. The bucket key can be any characters (ex. dhtsensor1).

Since we will be measuring the temperature from the DHT22 sensor, signalname will be labeled as temperature.

//-------- User Settings -----------

const char* ssid = "SSID NAME";

const char* password = "WiFi PASSWORD";

const char* accesskey = "INITIAL STATE ACCESS KEY";

const char* bucketkey = "INITIAL STATE BUCKET KEY";

const char* signalname = "temperature";

//---------------------------------

Read Sensor & Send Data

This part of the code will read the DHT temperature and send the temperature value to Initial State.

float t = dht.readTemperature(true);

url += accesskey;

url += "&bucketKey=";

url += bucketkey;

url += "&";

url += signalname;

url += "=";

url += t; String url = " https://groker.init.st/api/events?accessKey= ";url += accesskey;url += "&bucketKey=";url += bucketkey;url += "&";url += signalname;url += "=";url += t; Serial.print("*** requesting URL");



ask.begin(url); //Specify the URL



int httpCode = ask.GET();



if (httpCode > 0) {

String payload = ask.getString();

} else {

Serial.print("Error on HTTP request");

}

ask.end(); //End

Serial.print("*** End ");

delay(10000);

}

Temperature Dashboard

Now that you’ve built the ESP32 temperature sensor and the code is running, it’s time to look at what data is being sent. Go to your Initial State dashboard to view the temperature data.

At first your dashboard should look something like this.

Initial State Dashboard for Temperature Data Streams

What you have the option to do is change the chart type, add more Tiles, change the background, view the data in Waves, and set a Trigger to alert you when values reach certain thresholds.

Initial State Dashboard with Background Images

You can have multiple sensors sending to the same dashboard. You can also send humidity and pressure data from the same sensor to your dashboard. You can use this system to monitor your home, greenhouse, server room, fridges, and more.

Use Read API to GET Temperature Data

If you want to use your ESP32 to read temperature data instead of sending it, that is possible with Initial State’s Read API. You can GET your latest data values from any of your Initial State buckets. Choose to read all signals in the bucket or a specific one.

By default read access is disabled for your buckets so you will need to enable read access on any bucket you want to GET data from. To enable read access on a bucket, go to your bucket settings and check the box for “Allow Read Latest Value API.”

The read all the signals in your data bucket, use the code below.

To read only a specific single in your data bucket use the code below.