Table of Contents
Introduction
A temperature sensor circuit is an electronic device that detects temperature changes and responds accordingly. This type of circuit is commonly used in safety applications, such as fire alarms, overheat protection systems, and temperature monitoring in electronic devices. The circuit operates by sensing temperature variations through a thermistor, which influences the activation of transistors to trigger an alert mechanism. The simplicity and efficiency of this circuit make it an ideal choice for DIY electronics enthusiasts and practical applications in various industries.
Circuit Components
| S.No | Component Name | Value | Quantity |
|---|---|---|---|
| 1 | Thermistor | 10KΩ | 1 |
| 2 | BC547 Transistor | NPN | 2 |
| 3 | Resistor | 12K Ohm | 1 |
| 4 | Buzzer | 9V | 1 |
| 5 | Battery | 9V | 1 |
BC547 Pinout
The BC547 is an NPN bipolar junction transistor (BJT) with three pins:
- Collector (C): The output terminal where current flows out.
- Base (B): The control terminal that regulates the transistor’s switching action.
- Emitter (E): The terminal through which current exits the transistor.
The standard pin configuration for BC547 (when looking at the flat side with leads facing downward) is:
- Left: Collector (C)
- Middle: Base (B)
- Right: Emitter (E)
Circuit Diagram
Circuit Explanation
The circuit functions based on the temperature-dependent behavior of the thermistor, which controls the operation of two BC547 transistors. Here’s how the circuit works:
- Thermistor Behavior:
- The thermistor is a Negative Temperature Coefficient (NTC) type, meaning its resistance decreases as the temperature rises.
- Under normal conditions, the thermistor has a relatively high resistance, limiting current flow through the circuit.
- Transistor Activation:
- When the temperature increases beyond a certain threshold, the thermistor’s resistance drops, allowing more current to pass through.
- This increase in current turns on the first BC547 transistor, which acts as a switch.
- The activation of the first transistor supplies base current to the second BC547 transistor, causing it to turn on as well.
- Buzzer Activation:
- Once the second transistor is switched on, it completes the circuit for the buzzer.
- The buzzer receives power from the 9V battery and produces an alert sound.
- This alert indicates that the temperature has exceeded the predefined limit.
- Circuit Reset:
- When the temperature drops, the thermistor’s resistance increases again.
- This reduces the current flow, turning off the first transistor and, subsequently, the second transistor.
- As a result, the buzzer stops sounding, bringing the circuit back to its initial state.
Applications
- Overheat protection circuits.
- Fire alarm systems.
- Temperature monitoring in electronic devices.
This simple yet effective temperature sensor circuit can be used in various applications where heat detection is required. By adjusting the thermistor and resistor values, you can fine-tune the circuit’s sensitivity to temperature changes.
