Fridge door alarm

Hatchnhack Design
Fridge door alarm
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A Fridge door Alarm is a simple PCB project designed to detect & inform the status of any refrigeration unit’s door: whether it’s open or not. It produces a monotonous beeping noise if the fridge door is left open for too long by an accident. Its common use is in refrigerators, Temperature Controlled Freezers & beverage coolers.

Apparatus:

  • Resistors ( 10kὨ - 1;  470kὨ -2 ;    100kὨ  -2 )

  • Electrolytic Capacitor ( 47 uF)



    They are integral to the functionality and reliability of fridge door alarm circuits, providing power stability, noise filtering, timing, and energy storage capabilities.

  • Ceramic Capacitor ( 0.1 uF)


    By using both electrolytic and ceramic capacitors, the fridge door alarm circuit can achieve stability, and noise immunity, guaranteeing it works accurately and productively.

  • LED-red


    The red LED in a fridge door alarm is an essential component. It enhances user awareness and ensures that the fridge door is promptly closed. And by this it maintains the efficiency and effectiveness of the refrigerator.

  • NE555 TIMER X 2


    Using two NE555 timers in a fridge door alarm circuit allows for a reliable and efficient way to monitor the door status and alert users if the door is left open. The first timer provides a delay to avoid false alarms from brief entryway openings, and on the other hand the second timer produces an occasional caution to ensure the user sees the issue.

    This arrangement joins both timing and control capabilities, utilizing the flexibility of the NE555 timer ICs.

  • BUZZER

    The buzzer is integrated with NE555 timers in monostable and a stable modes ensures a reliable and effective alarm system, provoking users to close the refrigerator entryway quickly and keep up with the productivity and security of their refrigerator

  • LDR


    Using an LDR in a fridge door alarm system provides an efficient and non-contact method for detecting door status. It is combined with NE555 timers, and ensures that an alarm is triggered if the door remains open for too long. It also helps to prevent food spoilage and energy loss.

  • Battery Clip/ POWER supply


    9V power supply is used for this circuit.  A battery clip offers portability and backup power and on the other hand an external power supply provides consistent power for continuous operation.

  •  DIODE ( 1N4007 )

    1N4007 diode in a fridge door alarm circuit enhances reliability of the system. It provides reverse polarity protection, seamless switching between power sources, and general protection against surges and incorrect current flow.
     

Typically, refrigerators and freezers are in constant use in the summer months and so it is important to ensure that the door is not open for any longer than is necessary. Otherwise, the fridge or freezer will not be able to keep the contents cool. And it will cost more money to needlessly run the fridge’s compressor in a futile effort to keep the contents cool. Even the most diligent fridge user may sometimes leave the door of the fridge or freezer open without realizing it. And tilting the fridge or freezer slightly backward so that the door will fall shut is not completely fool proof as there may be an obstruction inside the door.

The obstruction could be because an item inside the compartment has moved or fallen over or because the compartment is too full. This is where the Fridge Alarm is useful. It warns when the door of the refrigerator or freezer is left open for longer than a preset time period. It is great for indicating when someone is standing with the door open for too long and a real asset in warning when the door looks shut but is still partially ajar.

The fridge alarm operates by detecting when any light enters the compartment area. Therefore, it is just as useful for freezers (which normally do not have a light) as it is for fridges (which normally do). As long as there is some ambient light which the alarm can react to, it will operate.

Circuit Diagram :

 

Operation:

  • The operation of this circuit relies on the interaction between two NE555 ICs. IC1 evaluates & corresponds with the input of the LDR while IC2 uses the output sent from IC1 to regulate the buzzer as per the position of the fridge door.
  • Both the 555 ICs are wired as Astable Multivibrators. A Light Dependent Resistor (LDR) is used as the light sensor for this circuit. It is basically a light-sensitive device that works on the principle of photo-conductivity. An LDR is made of semiconductors with high resistance. When light falls on the device, the output of the LDR varies, and this output can be used to buzz an alarm for the door open circuit. It is connected in parallel to the timing capacitor C1 of 555 timers, IC1.

Schematic Capture:



PCB Layout:


Working:

The entire circuit is powered by a 9V battery. When the fridge door is closed, it is dark and the resistance of the LDR is nearly 1MὨ as given in datasheet. The output voltage of the potential divider appears across the capacitor and it remains in charged condition (Voltage higher than 2/3Vcc) making the output LOW. When we open the Fridge, the light falls over LDR which lowers down the resistance of LDR and causing the capacitor to discharge which in this RC combination it is 30 secs.

After this (Voltage lower than 2/3Vcc), the output starts to oscillate at certain frequency and output is HIGH. Again, the capacitor charges and reaches a threshold continued by discharge of the capacitor. This continues till the LDR resistance goes high which will happen in the absence of light (door is closed).

This makes the second 555 timer to oscillate and the output becomes HIGH and LOW causing the buzzer connected to output to beep in a pattern which is combinational cause of the first timer oscillations and the second timer internal oscillation. During HIGH condition of first timer output, the second timer master reset will happen. Thus, the capacitor C2 charges (Voltage higher than 2/3Vcc) and output goes LOW. In a short span the capacitor starts to discharge (Voltage lower than 2/3Vcc) causes the output HIGH. Thus, the buzzer connected to output becomes pulsed beep sound.

3D Visualizer :

 

This will enhance your understanding, improves debugging, and provides a professional presentation of the circuit.

Advantages :

  • Avoid wasting electricity by unnecessarily keeping the fridge door open for a long time.
  • Decrease in food spoilage.
  • Less energy consumption.
  • Easier maintenance and troubleshooting.
  • Adjusting the alarm sensitivity or delay settings through software updates.
  • Reduces electricity bills by preventing unnecessary energy wastage.

 

Conclusion:

Hence, this Fridge Door Alarm Circuit is a good solution which will indicate the user about the door in prolonged open condition. We can also set different pre-set time after which the audible indication has to be given. This is done here by using the versatile 555 timer IC under astable multivibrator mode and LDR. As soon as we open the Door of refrigerator, LDR senses it and start the countdown using 555 Timer, and after a preset time the buzzers starts beeping as alarm signal.

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