Here is an interesting project of a very sensitive, reliable, and low-cost temperature sensor using a diode (1N4007). It must be unusual for you to hear that a diode performing a temperature sensing task, but it is possible.
A diode can sense temperature because of its forward voltage. It changes when the temperature changes and that’s how you can get a good temperature sensor at a low cost without using an NTC thermistor or any other thermal sensors. Or if you want to make a temperature sensor and you don’t have a thermal sensor available with you then you can make it with this circuit. It gives accurate results just like any normal temperature sensor.
Hardware Components
The following components are required to make Temperature Sensor Circuit
| S.no | Component | Value | Quantity |
|---|---|---|---|
| 1. | DC Supply | 9-12V | 1 |
| 2. | Resistor | 1K | 2 |
| 3. | Transistor | 2N4401 | 2 |
| 4. | Diode | 1N4007 | 2 |
| 5. | Relay | 9-12V | 1 |
| 6. | Variable Resistor | 10K | 1 |
2N4401 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N4401
Temperature Sensor Circuit
Working Explanation
The operating voltage of this circuit s 9-12 volts. There are two 2N4401 transistors used in this circuit that are working as switches. When the diode D1 is used to sense the heat so when it receives heat the transistor Q1 will be activated and provides 0.7 V at the base of the transistor Q2 and it activates as well. This will activate the relay switch.
Anything connected with the relay will be turned on as well. A 10K variable resistor is used to adjust the circuit to activate the relay at the desired temperature.
Applications and Uses
Since there is a relay switch at the output of this circuit that’s why it can be used in various applications such as,
- Fan
- Heat sensor Alarm
- Overheating indicator
