In this tutorial, we are making a project on a Cold sensor switch. This circuit is very sensitive and can easily be used to sense cold or low temperature, it can activate any device connected with the relay on your desired coldness/low temperature. The temperature sensing is done by an NTC thermistor. The thermistor is a device whose resistance is dependent on the temperature.
When temperature increases its resistance decreases and at low temperature, its resistance is increased.
Hardware Components
The following components are required to make Cold Sensor Switch Circuit
| S.no | Component | Value | Quantity |
|---|---|---|---|
| 1. | DC Supply | 9-12V | 1 |
| 2. | Thermistor | 100K | 1 |
| 3. | Resistor | 1K | 2 |
| 4. | Transistor | 2N4401 | 2 |
| 5. | Relay | 12V | 1 |
| 6. | Diode | 1N4007 | 1 |
| 7. | Variable Resistor | 10K |
2N4401 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N4401
Cold Sensor Switch Circuit
Working Explanation
The operating voltage of this circuit is 9 to 12 volts. A 100K thermistor is used to sense the temperature and two 2N4401 NPN transistors are used as switches in this circuit. Initially, at high temperatures, the resistance of the thermistor will be minimum and it will keep the circuit deactivated. When the temperature is low thermistor’s resistance is increased and it will activate the transistor. The transistor Q1 will now give 0.7v at the base of the transistor Q2 which switches ON and activates the relay.
A 10K variable resistor or a potentiometer is used to adjust the circuit to activate the relay at your desired low temperature. The relay used in the circuit should have the same value as the input voltage.
Applications and Uses
Since we have a relay switch at the output of this circuit you can connect any load like a fan, etc., to operate it at your desired temperature.
