IR Digital Thermostat for FAN

Description: This circuit allows the use of the keys "1, 2, 3, 4" on a Philips TV IR remote to control three relays. The key "4" specifically activates the over-temperature alarm. The LM35 temperature sensor can detect temperatures from 0°C to 100°C, but it outputs an analog signal that the microcontroller cannot interpret. Therefore, an ADC0804 (analog-to-digital converter) is employed to convert the analog signal into digital data, which is then sent to port 1 of the microcontroller. The microcontroller processes this data and displays the temperature on an LCD connected to port 2. The control pins of the LCD are linked to port 0, which also manages the relays and the alarm. To drive the relays, the ULN2003 chip is utilized, as the microcontroller pins do not supply sufficient current. The relays, being inductive loads, generate reverse current, necessitating the use of the ULN2003. Pins 1 to 7 serve as inputs, while pins 10 to 16 are the corresponding outputs. Pin 8 is grounded, and pin 9 connects to the output of a 7808 voltage regulator, while a 7805 voltage regulator powers the rest of the circuit. A standard buzzer is driven by an LM555 timer/oscillator chip, configured as a monostable multivibrator, with the buzzer connected to pin 3. An IR module can be used, with its data output connected to pin 10 of the microcontroller. The relay connected to pin 13 of the ULN2003 activates when the temperature exceeds 40°C, allowing for the connection of a fan to this relay. A standard PCB is utilized, with a PCB file included in a zip file that can be opened with EAGLE software. The PCB should be printed on glossy paper, ensuring the print is on the copper side. An iron can be used to transfer the print onto the PCB. Afterward, the PCB should be immersed in an etchant, such as FeCl3 (ferric chloride). Once the PCB is ready, it should be rinsed thoroughly to remove any FeCl3 residue, and the print can be removed using steel wool. Finally, holes can be drilled, and components can be placed.

The circuit is designed to provide a user-friendly interface for temperature monitoring and control. The integration of the Philips TV IR remote allows for convenient operation, enabling users to activate or deactivate relays and alarms from a distance. The LM35 temperature sensor offers a reliable method for measuring temperature, while the ADC0804 ensures that the microcontroller receives data in a format it can process. The microcontroller's role extends to displaying the temperature on an LCD, providing real-time feedback to the user.

The ULN2003 chip is essential for controlling the relays, as it can handle the higher current requirements of inductive loads, protecting the microcontroller from potential damage. The use of a buzzer driven by the LM555 timer adds an auditory alert for the over-temperature condition, enhancing the circuit's functionality.

For assembly, the use of a standard PCB simplifies the process, allowing for a compact and organized layout of components. The step-by-step instructions for transferring the print onto the PCB and etching it ensure that even those with minimal experience can successfully create the circuit. Drilling holes for component placement completes the assembly process, enabling the final circuit to be operational. This design exemplifies a practical application of electronics in temperature monitoring and control systems.Another feature of this circuit is that you can use the keys "1, 2, 3, 4" of a Philips TV IR remote to turn on or off three relays, The key `4` is used to turn on or off the over temperature alarm. package. LM35 can sense temperature from 0 C to 100 C but it gives analogue output the microcontroller does not understand analogue data, so ADC0804 (anal

ogue to digital converter) is used to convert it to digital form. This digital data is given to port 1 of microcontroller. (See the circuit diagram) this data is processed by microcontroller and temperature is displayed on lcd connected to port 2. The control pins of lcd are connected to port 0. port 0 also controls the relays and alarm. The ULN2003 chip is used to drive the relays because the microcontroller pins don`t have enough current to drive them.

so relays cant be connected to microcontroller pins directly further more the relays are inductive load and reverse current is generated in them. Pin 1 to 7 are the inputs and 10to 16 are respective outputs. Pin 8 is ground and pin 9 is connected to the output of 7808 voltage regulator. The 7805 voltage regulator drives rest of the circuit. I used a standard buzzer driven by LM555 timer/Oscillator chip. The chip is wired as a monostable multivibrator and at its output (i. e. pin no 3) a buzzer is connected. Use any IR module and connect its Data out to pin 10 of microcontroller. The Relay connected to pin 13 of ULN2003 turns on when temp rises above 40 C so connect the fan to this relay.

Use a standard pcb. A pcb file is included in the zip file it opens with a software called EAGLE You can download the demo version here its quiet simple and easy to use. So print the pcb on a glossy paper. now place the glossy paper on the pcb. The print should be on the copper side now use an iron to transfer the print on the pcb. After you are done dip the pcb in any enchant I used FeCl3 (ferric chloride). When your pcb is ready pour lots of water to remove any FeCl3 and remove the print using steel wool. Now drill holes and place components.