Prerequisite Internet Accounts

1. An Adafruit IO account, you can sign up for free account here.
1. An IFTTT Account, you can join IFTTT here.


Clone this repo to your computer, or you can download the directory for this project here

Once you downloaded the project files you'll need to create a config.h file and fill in your Adafruit IO and WiFi credentials.

  1. In the FreezerTempAlert folder create a new text file called config.h
  2. Copy and paste the code below into that that file and save:
/************************ Adafruit IO Config *******************************/

// visit if you need to create an account,
// or if you need your Adafruit IO key.
#define IO_USERNAME "your-username"
#define IO_KEY "your-key"

/******************************* WIFI **************************************/

#define WIFI_SSID "your-ssid"
#define WIFI_PASS "your-password"

#include "AdafruitIO_WiFi.h"


3. Find your Adafruit IO credentials in the top right corner of the Adafruit IO webpage.

4. Copy and paste them in here between the quotes:

#define IO_USERNAME "your_username"
#define IO_KEY "your_key"

Remember to treat your key like a password

5. Next you will need to add the WiFi SSID, or network name, and the password. Note: The code doesn't support WiFi networks that use a captive portal.

#define WIFI_SSID "your_ssid"
#define WIFI_PASS "your_pass"

6. Open FreezerTempAlert.ino and change the threshold temperature to the temperature you wanted to be alerted at. The default temperature is -50 Celsius.

// Set the temperature you want to be alerted at
const float thresholdTemperature = -50;

Flashing the code

  1. Follow the first section of this guide to add the ESP32 extension to the Arduino IDE.
  2. Install the libraries listed below using Arduino's Library manager. If you have used the library manager before, here is a helpful guide.
    • Adafruit IO Arduino
    • Adafruit MCP9600
      • Note: If you're prompted to install other dependencies for these libraries, select Install All
  3. With FreezerTempAlert.ino open in the Arduino IDE select Tools > Board > Adafruit ESP32 Feather
  4. Select the active COM Port in Tools > Port
  5. Press the Upload button

    Arduino upload button

  6. Open the Arduino serial monitor to verify that everything is working properly on the board.

  7. Go back to and check that both the temperature feed and the temp_alert feed were created.

Setting up IFTTT

You'll use If This Then That (IFTTT) to set up automated alerts to your email any time the temperatures goes above a threshold. The threshold is set to -50c by default.

  1. Log in to your IFTTT account and press the Create button in the top navigation. 
  2. Select the + button to add a trigger.

3. Search for Adafruit

4. Follow the prompts to connect and authenticate your Adafruit IO account.

5. Once your account is connected choose the Any new data trigger.

6. Select temp_alert from the drop down menu and press Create trigger

7. Select the next + to set your action.

8. Scroll down or search for the Email action

If this is the first time you're using the email action a pin will be sent to you to confirm that you are the owner of the email account.

9. Customized the email message and select create action 

10. Finally select finish, your IFTTT service is ready to go.

Installing the monitor

Now that you project is built and your services are setup you can install the thermocouple in the freezer. You can use a binder clip or a magnet to keep it in place. The Feather Huzzah32 board should be kept outside the freezer. Many breadboards come with an adhesive back, you can use that to secure your project to the side of the freezer.

Sensor installed in a home freezer to collect data

This guide was first published on Jan 27, 2021. It was last updated on Mar 08, 2024.

This page (Code) was last updated on Mar 08, 2024.

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