In this tutorial, we are making a project of a Simple temperature sensor circuit. This circuit activates an LED when it senses or receives heat so you can also call this circuit a heat sensor circuit. Apart from its uses, If you are a beginner who just wants to make an easy and interesting project this circuit is ideal for you. It is an inexpensive and simple circuit that is only using a few components and can be made in a very short time easily.
This circuit is very sensitive to heat since we connected two transistors as a Darlington pair. Other than that we have used an LED along with a current limiting resistor, a variable resistor, and a thermistor. Thermistors are used to limit the passage of current through them according to the temperature. When the temperature is low they have higher resistance and as the temperature increases their resistance starts decreasing allowing the current to flow.
Both the transistors are BC547. These transistors are NPN bipolar junction transistors, they are mainly used to amplify the current. A small current at its base controls a large current at emitter and collector terminals.
Hardware Components
The following components are required to make Temperature Sensor Circuit
| S.no | Component | Value | Quantity |
|---|---|---|---|
| 1. | Battery | 9V | 1 |
| 2. | Thermistor | – | 1 |
| 3. | Resistor | 390Ω | 1 |
| 4. | Transistor | BC547 | 2 |
| 5. | LED | – | 1 |
| 6. | Variable Resistor | 10K | 1 |
BC547 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of BC547
Temperature Sensor Circuit
Working Explanation
The working of this circuit is simple. It is operating at 9 volts. Initially, when there is no heat the circuit will remain turned off. When the thermistor receives heat its resistance will be decreased and it will let the current flow.
This will activate both the transistors and the voltage will be passed to LED and it will light up. A variable resistor of 20K ohms is used to adjust the circuit for activation of LED on the required temperature or heat.
Applications and uses
This device is ideal to use where you don’t want any device or equipment to be overheated, the circuit is compact so it can fit anywhere.
