This freezer alarm circuit is like a tiny guard for your frozen treats.
It uses a special sensor thermistor to keep an eye on the temperature.
If the freezer gets too warm, the circuit sounds an alarm buzzer to let you know somethings fishy or melty.
This way, you can take action to save your food before it spoils.
Circuit Working:
Parts List:
| Category | Component | Quantity | Notes |
|---|---|---|---|
| Resistors | 220Ω | 1 | 1/4 watt |
| 100Ω | 1 | 1/4 watt | |
| Thermistor | NTC 10k | 1 | |
| Preset | 100k | 1 | |
| Capacitors | Electrolytic 4.7µF 25V | 1 | |
| Semiconductors | SCR BT169 | 1 | |
| MOSFET BS170 | 1 | ||
| Diode 1N4001 | 1 | ||
| Miscellaneous | Mechanical Buzzer 6-9V | 1 |
Here is a basic freezer alarm circuit designed to be highly sensitive with a buzzer.
The circuit triggers an audio alert when the temperature inside the freezer box exceeds a predetermined level.
It operates on a 9V DC supply, which can be provided by a standard 9V alkaline battery.
A small thermistor R1 of the negative temperature coefficient NTC type serves as the sensor for monitoring the freezers status.
Additional components T1 and T2 are employed to drive a mechanical buzzer rated at 6 to 9V.
When the sensor detects a rise in temperature the buzzer activates and continues beeping until power to the circuit is cut off.
To enable this ON/OFF and reset function a small DC toggle switch can be inserted into the positive power supply.
Electrical characteristic for NTC 10k
| PARAMETER | VALUE | UNIT |
|---|---|---|
| Resistance value at 25 °C | 4.7K to 100K | Ω |
| Tolerance on R25-value | [\pm1.0~to\pm5.0] | % |
| B25/85-value | 3435 to 4190 | K |
| Tolerance on B25/85 | [\pm0.5~to\pm1.5] | % |
| Operating temperature range at zero dissipation | -40 to 105 | °C |
| Maximum power dissipation at 55 °C | 100 | mW |
| Accuracy of temperature measurement (for 1% types) | ± 0.5 between 0 and 40 <br>± 1.0 between -40 and 80 | °C |
| Dissipation factor δ (in still air) | ≈ 3 | mW/K |
| Response time (in oil) | ≈ 2.5 | s |
| Climatic category (LCT/UCT/days) | 40/105/28 | |
| Minimum dielectric withstanding voltage between leads and coated body | 500 | Vrms |
| Weight (40 mm length) | 0.2 | g |
How to Build:
To build a Simple Freezer Alarm with Buzzer Circuit follow the below mentioned steps:
Prepare the PCB:
- Arrange the components on the PCB according to the circuit diagram.
Solder the Components:
- Solder the components onto the PCB ensuring all connections are secure.
Connect the Thermistor R1:
- Connect one end of the thermistor R1 to the positive power supply and the other end to the base of transistor T1.
Connect Transistors T1 and T2:
- Connect the collector of T1 to the base of T2 and connect the emitter of T1 to the negative power supply.
Connect the Buzzer:
- Connect one terminal of the buzzer to the collector of T2 and the other terminal to the positive power supply through a diode 1N4007.
Add the Reset Switch:
- Connect a small DC toggle switch between the positive power supply and the collector of T1 for the ON/OFF and reset function.
Connect the Battery:
- Connect the 9V alkaline battery to the positive and negative power supply.
Note:
- Once you have assembled the circuit, test it by placing the thermistor in the freezer.
- If the temperature rises above the preset level, the buzzer should sound.
- Adjust the sensitivity by changing the value of R1 or other components as needed.
Conclusion:
To conclude, a Freezer Alarm with Buzzer Circuit is a useful and relatively simple electronic device that helps prevent food spoilage by alerting users when the temperature inside a freezer exceeds a predetermined level.
It can be a valuable addition to any home or commercial freezer providing peace of mind and potentially saving money by avoiding food loss.
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