Please help me understand how this temperature alarm circuit

Please help me understand how this temperature alarm circuit works. I am fairly certain that R1, R2, R3 are a voltage divider, but this is supposed to be a circuit to trigger a temperature alarm below 50 degrees and above 100 degrees (farenheit). I do not understand how to prove that temperature range, and I do not understand how the temperature signal gets to the LED\'s. I am guessing that the opamps are a comparator, because I think I have seen that before.

What part do all of the transistors play?

Why are there so many power sources on here?

Also, where would I measure to prove all of this?

Lastly, thank you in advnance for your time!

Solution

Here is the explanation

Volatge across Thermistor gives temperature in terms of voltage,using thermistor datasheet you can find the resistance to temperature variation ,once you find resistance for 50 deg as well as 100 deg you can find volatge across thermistors using volatge diveder rule as it is connected as simple POT i.e Potentiometer or variable resistance

The calculated volatges are reference for 50 deg as well as 100 deg temperatures the voltage divider R1 R2 R3 are placed such that they provides voltage corresponds to those temperatures,in this case they are

5/3 V for 50 deg and 10/3 V for 100 deg as you can see from volatge divider rule V/(R1+R2+R3) gives current and

as all resistances are equal ,volatge across each one is 5/3 Volts as they are 3 resistors and 5 V is voltage source \'

Now comparator compares these voltages i.e(corresponding to 50 and 100 deg) with real time temperature

coming in terms of voltage across thermistor POT ,the output of the comparator gives whether temperatue is below 50 deg or above 100 deg

R4 and R5 are pull up resistors required for biasing the op-amp ,these output from op-amp comparators

are given to transistors they acts as switches here,these transistors drives LED\'s which will on /off giving alarm whether temperature is below 50 or above 100 and another set of transistors Q3 and Q4 are used because these LED\'s need more current and requires higher voltage so those transistors VCC is 12 V