Temperature detection using led

Temperature detection using led

The circuit has two LEDs (D1 and D2), they are controlled by the temperature of the surrounding. The  IC LM35 is used as temperature sensor here. Output of LM35 increases by 10mV per degree rise in temperature. Output of LM35 is connected to  non inverting input of the opamp CA3130.The inverting input of the same opamp can be given with  reference voltage using POT R2. If the reference voltage is 0.8V, then the voltage at the non inverting input (output of LM35) becomes 0.8V when the temperature is 80 degree Celsius. At this point the output of IC3 goes to positive saturation. This makes the transistor Q1 On and LED D1 glows. Since the base of Q2 is connected to the collector of Q1, Q2 will be switched OFF and LED D2 remains OFF. When the temperature is below 80 degree Celsius the reverse happens.IC1 produces a stable 5V DC working voltage from the available 9 V DC supply. If you already have a 5 V DC supply then you can use it directly

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                                                                     q1, q2 be NPN transistor