In the world of home automation, a smart thermostat is one of the most functional and rewarding projects to undertake. It allows you to monitor and control your home’s heating and cooling systems with ease, and it can be a significant energy saver. For this project, we will create a smart home thermostat using the PR36MF21NSZF temperature sensor, which will read the room’s temperature, display it, and allow for basic control over an HVAC (heating, ventilation, and air conditioning) system.

Project Overview:

In this project, we’ll build a smart home thermostat that reads the room temperature with the PR36MF21NSZF sensor, displays it on a simple digital screen, and allows you to adjust the desired temperature range. By incorporating a relay, we can switch the HVAC system on and off when the temperature exceeds the set threshold. The system will be powered using a microcontroller, which will handle reading the sensor data, controlling the display, and activating the relay when needed.

Components Needed:

● PR36MF21NSZF Temperature Sensor: This is a precise temperature sensor used in industrial and consumer applications, ideal for monitoring room temperature in this project.

● Microcontroller (e.g., Arduino or ESP32): A microcontroller will read the temperature sensor’s data and control the relay to activate the HVAC system.

● Relay Module: A relay will control the HVAC system by switching the power on and off when the desired temperature is reached.

● LCD Display (16x2 or similar): The LCD display will show the current temperature and the setpoint temperature.

● Push Buttons: These will allow the user to adjust the setpoint temperature up or down.

● Power Supply: A 5V or 12V power supply, depending on the requirements of your components.

● Resistors: For current-limiting and voltage division.

● Wires, Breadboard, and Connectors: For easy assembly and prototyping.

Understanding the PR36MF21NSZF Sensor

The PR36MF21NSZF is a high-precision temperature sensor. It uses a thermistor to measure the temperature and provides an analog output. This sensor is perfect for applications where accurate temperature monitoring is necessary, such as in HVAC systems, home appliances, and medical devices. In this project, the sensor will provide an analog voltage output that corresponds to the temperature in the room, which the microcontroller will read and use to control the system.

The PR36MF21NSZF has a wide operating range, making it perfect for both hot and cold environments. For this project, it will be used to monitor room temperature and ensure that the HVAC system runs only when needed.

Assembling the Circuit

Step 1: Wiring the Temperature Sensor

Start by connecting the PR36MF21NSZF temperature sensor to the microcontroller. The sensor has three pins:

● VCC (Power): Connect this to the 5V pin of your microcontroller.

● GND (Ground): Connect this to the ground (GND) pin of the microcontroller.

● Output (Analog): This is the pin that provides the analog temperature data. Connect this to one of the analog input pins on your microcontroller (e.g., A0 on an Arduino).

The PR36MF21NSZF outputs an analog voltage that changes with temperature. This voltage is directly proportional to the temperature, and the microcontroller will read this voltage to determine the room’s temperature.

Step 2: Connecting the LCD Display

The LCD display will show the current room temperature and the desired temperature setpoint. To connect the LCD:

● VCC: Connect to the 5V pin of the microcontroller.

● GND: Connect to the ground (GND) pin of the microcontroller.

● SDA and SCL (I2C Communication): Connect these to the appropriate pins on your microcontroller (typically A4 and A5 on an Arduino for I2C communication).

The LCD display will continuously show the current temperature as it is read from the PR36MF21NSZF sensor. It will also allow the user to see the setpoint temperature that can be adjusted using the push buttons.

Step 3: Wiring the Push Buttons

The push buttons will allow the user to adjust the desired temperature setpoint. You’ll need two buttons:

● Increase Button: This button will increase the setpoint temperature.

● Decrease Button: This button will decrease the setpoint temperature.

Each button should have one terminal connected to a digital pin on the microcontroller and the other terminal connected to ground. Use pull-up resistors to ensure stable readings when the buttons are pressed.

Step 4: Adding the Relay to Control the HVAC System

To control the HVAC system, you will use a relay. The relay module will act as a switch that turns the HVAC system on or off based on the room temperature. Here's how to connect the relay:

● VCC: Connect to the 5V pin on the microcontroller.

● GND: Connect to the ground pin on the microcontroller.

● IN (Control Pin): Connect this to a digital output pin on the microcontroller (e.g., pin 8).

● COM (Common Pin): This is the terminal that will connect to one terminal of the HVAC system’s power.

● NO (Normally Open Pin): This terminal will connect to the HVAC system's power line. When the relay is activated, the connection between COM and NO will close, allowing current to flow to the HVAC.

Make sure the relay you choose is rated for the voltage and current requirements of your HVAC system. For safety, use a relay that is designed to handle the high voltage of your HVAC’s power supply (e.g., 120V AC or 240V AC).

Step 5: Powering the System

Ensure that your power supply is adequate to power both the microcontroller and the relay. For most microcontroller-based projects, a 5V power supply should be sufficient. However, the relay may require a separate 12V or 24V supply depending on your HVAC system's requirements.

Make sure the power lines for both the microcontroller and the HVAC system are properly separated to avoid damage to your components.

Configuring the System

Once the circuit is assembled, you need to configure the logic that will drive the system.

Step 1: Reading the Temperature

The microcontroller will read the analog signal from the PR36MF21NSZF sensor. The sensor will output a voltage that corresponds to the room temperature. The microcontroller will convert this voltage into a usable temperature value and display it on the LCD.

Step 2: Displaying the Temperature

The LCD will display the current temperature, and it will also show the user’s desired setpoint temperature. The setpoint can be adjusted using the increase and decrease push buttons. Each button press will modify the setpoint by a set amount (e.g., increasing or decreasing by 1°C).

Step 3: Controlling the HVAC

Based on the difference between the current temperature and the setpoint, the microcontroller will control the relay. When the temperature exceeds the setpoint, the HVAC system will be turned off. When the temperature falls below the setpoint, the HVAC system will be turned on to maintain the desired environment.

Step 4: Fine-Tuning the System

To improve the system’s reliability, you can add a small hysteresis feature to prevent the system from rapidly switching the HVAC system on and off when the temperature is very close to the setpoint. This can be done by introducing a small deadzone, such that the HVAC system only activates if the temperature is 1-2°C below the setpoint.

Final Thoughts

Building a smart thermostat using the PR36MF21NSZF temperature sensor is a fantastic project that merges home automation with energy efficiency. It introduces you to various electronic concepts, such as analog-to-digital conversion, relay control, and sensor interfacing, while also giving you a practical application that you can use in your home.

Once you’ve completed the basic thermostat functionality, you can expand the project further. For example, you could add Wi-Fi capability to control the thermostat remotely via an app or add a scheduling feature that adjusts the setpoint at different times of the day. You can also incorporate more sensors, such as humidity or motion sensors, to create a more advanced smart home automation system.

With the PR36MF21NSZF sensor, your thermostat will provide precise and reliable temperature measurements, allowing you to create a thermostat that will help maintain comfort in your home while reducing energy consumption.