Ice warning alarm 12V

  
The circuit warns car drivers when the air temperature close to the ground approaches 0°C, thereby indicating possible formation of ice on the road surface. Op amp A1 is wired as a voltage level sensor. Op amp A2 is wired as an astable multivibrator which, by means of current buffer Trl, flashes a filament lamp at about 1 Hz. As air temperature falls, a point is reached when the voltage at pin 2 just rises above the voltage at pin 1.

The output of A1 is immediately driven into positive saturation, since it is operated open loop. This positive output voltage powers A2 through its V + connection on pin 9, starting the oscillator. The thermistor is a glass bead type with a resistance of about 20 ?? at 20°C. VR1 is adjusted so that the lamp starts flashing when the air temperature is Tto 2°C.




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