The figures below are showing two circuits of cold sensor. The circuit shown in figure 1 will activate an LED and a buzzer when the coldness will reach on the preset level. The circuit shown in figure 2 is using a relay switch at the output in the place of buzzer due to which it can activate any AC or DC appliance on the preset level of coldness. The level of coldness on which you want activate the circuit can be adjusted with the 20K variable resistor.
The circuits are using NTC thermistors. In this circuit the thermistors are used as a cold sensor. Normally you have seen the thermistors in heat sensor type circuits but it can also be used to sense coldness.
Working of the circuit is simple when the temperature will fall to the preset level of the circuit, then the 555 timer will activate an LED and a buzzer or relay till the temperature will rise from that level. You can also experiment with different thermistor and variable resistor values.
A good cold sensor alarm or switch can also be made using a 555 timer IC, The circuit is using a thermistor and very few discrete components. The circuit is very simple and using only 6 components. An LED is used for visual indication but you can remove it with its 470 ohms current limiting resistor to
Hello Readers, We frequently add new circuit diagrams, so do not forget to come back often. Thank you.