Road Ice Alarm electronic schematic circuit

This road ice alarm electronic circuit schematic use a LM3900 quad operational amplifier . As a temperature sensor this road ice alarm circuit use a thermistor  . When the temperature is around  36 degrees Fahrenheit (2.2 celsius degrees )  the LED connected on pin 4 at the LM3900 op amp will flashes at once about each one second  .  When the temperature is going down to 32 degrees Fahrenheit (0 degrees Celsius ) the led remains on  . Before you use this road ice alarm electronic circuit you need to calibrate it  . To calibrate the circuit you need to put the thermistor in a mixture of a crushed ice and water and adjust the variable resistor R2 until the LED is remaining on . The road ice alarm circuit needs to be powered from a 12 volts DC power supply circuit ( If you use it for car the car battery can be used for powering the circuit ) .