Temperature and Humidity Monitoring

This project is being specifically designed for monitoring temperature and humidity in a clean room. Temperature and humidity sensors are connected to ESP32 boards that send data to a central RPi. The end goal is to have this RPi make this data accessible from the Internet. In this project, Bluetooth is used. Many similar projects use MQTT which uses WiFi to transmit sensor data to the RPi instead. Bluetooth is used in this instance because offline data transmission is preferred.

Components used for this project

• Raspberry Pi 4 with power cable and MicroSD card w/NOOBS
• ESP32 boards
• USB to mini cable for each ESP32 board
• humidity and temperature sensors
• jumper wires
• PC (Windows 10) with mouse and keyboard

ESP32 setup

There are several ESP32 boards available, and any model should work. Note that certain ESP32 boards, including ESP32 DEVKIT DOIT which is used in this project, require holding the boot button when flashing.

Hardware setup

• Refer to the sensors user guide if available. The HTU21D-F sensor is used in this project.
• Refer to the ESP32 user guide as well for the pinout. Connect the sensor to the ESP32 with the jumper wires according the the pinouts. A breadboard can be used here but is not necessary.
• Connect the ESP32 to the PC with the USB mini cable.
• Download and install the appropriate driver for your ESP32 USB connection. The CP2104 USB driver was installed in this case.

Arduino IDE

• On a computer, download the appropriate Arduino installation file for the OS.
• Open Arduino IDE.
• Follow these instructions to install the ESP32 boards in Arduino.
  • In this case, select Tools --> Board --> ESP32 Arduino --> DOIT ESP32 DEVKIT V1 for the last step. Refer to the ESP32 user guide to determine the appropriate selection.
• Go to Tools --> Port and select the appropriate port for the USB connection.
  • If the port is uncertain, open Device Manager. The port associated with Silicon Labs CP210x is the correct port.
• Go to Tools --> Manage Libraries...
• Search for Adafruit HTU21DF and install.
• Open this project's ino file in Arduino.
• Change the last line of code to change the frequency of the sensor readings as needed.
  • delay(1000*30); takes measurements every 30 seconds.
• Click on the serial monitor (magnifying glass) with the baud rate of 9600.
  • In general, this number should match the value in Serial.begin(value);
• Upload the file to the ESP32.
  • Hold the boot button on the board until Connecting... appears at the bottom of the screen if needed.
• The serial monitor will flash some text to indicate if the sensor is connected or not. Sensor readings will start to appear shortly after.
• The ESP32 can now be moved from the computer to wall or battery power.

Raspberry Pi setup

Any RPi with Bluetooth should work for this project. In this case, RPi4 was used. The instructions below are for connecting Bluetooth for Raspian V10 Buster and may not apply to other versions of the Raspberry Pi OS. V11 Bullseye generally works better with enterprise WiFi systems and may not require all of the Bluetooth steps below.

Initial Setup

• Install the Raspbian OS and connect to WiFi. If WiFi is not available, use an Ethernet cable to connect to the Internet for the next step.
• From the main menu, go to Preferences --> Raspberry Pi Configuration --> Interfaces and enable Serial Port and SSH and save.
• At this point, the RPi can be accessed with secure shell (SSH) from another machine to make switching between this device and the ESP32 boards easier.
  • Get the IP address: ifconfig
  • Restart the system to fully enable SSH: sudo reboot
  • Refer to Section 4 in this link for OS specific instructions to access the RPi remotely.
• Install the latest updates. Enter the following in the remote RPi secure shell:
  • sudo apt update
  • sudo apt full-upgrade
  • sudo reboot

Bluetooth setup

• Create a serial port profile:
  • sudo nano /etc/systemd/system/dbus-org.bluez.service
  • Find this line: ExecStart=/usr/lib/bluetooth/bluetoothd
    • Add -C at the end of this line
    • Directly after this line, add ExecStartPost=/usr/bin/sdptool add SP
  • Ctrl+s to save and then Ctrl+x to exit.
  • Restart the system: sudo reboot
• Trust and pair the ESP32:
  • bluetoothctl
  • scan on - Look for the ESP32 and note the MAC address.
  • scan off
  • pair <ESP32 MAC address>
  • trust <ESP32 MAC address>
  • paired-devices - This should show the ESP32
  • help shows a list of valid commands in bluetoothctl
  • CTRL+X to exit bluetoothctl

HTML setup

• Follow the instructions listed here:
  • In a terminal window, enter sudo apt-get install apache2 -y
  • The Apache2 Debian Default Page should load when http://localhost is entered into a web browser on the RPi.
  • Get the RPi IP address from the terminal window: hostname -I
  • Any device on the same network can access this webpage by entering the RPI IP address in a web browser. For example: http://192.168.1.10
• Copy the html and css files to the folder /var/www/html.
  • The two html files are responsible for the content of the two pages of the website.
  • The .css file is responsible for the styling for the website.

Running the main program

• Download and run serial_read.py. Verify that txt files named after the ESP32 MAC address appear in the same directory as the Python script.
• Set the RPi to run this file automatically at startup. In this case, Method 1 was utilized.
• sudo reboot - Check for new measurements 2 minutes after startup.
• In a web browser, enter the IP address of the RPi. A graph of humidity readings should be visible.