Temperature Monitor with IC LM741 or LM301
Using a thermistor in the position shown makes a heat activated sensor. A change in temperature will alter the output of the opamp and energize the relay and light the LED. Swapping the position of the thermistor and 47k resistor makes a cold or frost alarm.

Temperature Monitor with IC [...]

This circuit uses a Dallas DS1621 temperature sensor which indicates the temperature of the device. The temperature sensor has a thermal alarm output, which becomes high when the temperature of the device exceeds a user defined value. This is the figure of the circuit.
When the temperature drops below a user defined value, the alarm output [...]

This circuit is describes about sensing air flow using microcontroller PIC16C781. In this circuit is using Programmable Switch Mode Controllers (PSMC) that combination between the Integrated Operational Amplifier, Digital-to-Analog Converter (DAC), and gated timer to construct a thermally operated air flow sensor with minimum external components. This is the figure of the circuit.
Air flow is [...]