2 ideas of Car overheat alarm circuit

This is a circuit sound alarm when an engine start spreading the heat. Although every car will have a temperature gauge. But in some cars. May be no warning if the engine is overloaded with heat. Or the driver may not have noticed the temperature gauge can cause problems.

The working of circuit

The circuit in Figure 1 When the temperature of the engine increases. The resistance of the thermistor decreases. Thermistor is connected to R1 for divide the voltage of the power supply to pin 2 of an op-amp IC1-LM741. This voltage will decrease as the temperature rises, by at VR1-100K is used to adjust a reference voltage at pin 3 of IC1. When a voltage at pin 2 lower than pin 3, IC1 will be switch close makes has voltage at output pin 6 to send to IC2.

The IC2 is connected as an astable multivibrator to the sound signal generator circuit Temperature level to cause the sound can be adjusted with VR1. The VR2 will determine the frequency of the sound. Thermistor used in this circuit, as beads. Has a negative temperature coefficient.(NTC) Thermistors are devices that are heat resistant and can pass it quickly. Suitable for adoption. Used in this circuit currents up to 10 mA.

The parts list.

R1: 4.7K
R2: 22K
RTH1: Thermistor NTC type
VR1,VR2: Variable resistors _100K

C1: 0.01uF 63V Polyester Capacitor
C2-100uF 16V Electrolytic Capacitor

The semiconductor
ZD1: Zener diode 5.1 volts
IC1: LM741 Op-amp
IC2- NE555 timer

Loudspeaker 8 ohms

Automobile heat Warning with LED

Warn the heat in an automobile

This circuit sets up in its automobile will perform to warn give testimony know before your car is will born the heat too much. By use main part electronic be IC 741 and Thermistors. By have LED Flasher with usual rate , when the temperature arrives at location value keeps with before VR1. When the temperature increases continuously LED as a result stick bright forever. By control checking temperature has with VR2. This circuit gives with power supply of an automobile has normally for the frequency of winking can fix with C1. A friend can see the detail adds in the circuit.

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what is the working of zener diode in this circuit?

Graham Macfarlane

Hi – great idea, Just wondering what sensor is required, where it is positioned and where the sensor input is fed into the circuit,




can ilook for the whole project

Vasundhara kakda

Can you please give a detailed and clear explanation of the above circuit.. Also specify why Zener diode has been placed… Hoping for an early reply

Vasundhara kakda

This circuit is wrong. It gives buzzer for every temperature. a transistor has to be used so that it switches on only for higher temperatures.

Saima khan

This circuit is blowing buzzer at every temperature. please tell me how it will work properly

Saima khan

It is giving buzzer at every temperature…

Abebe Alem

please give me brief explanation about working principle of this circuit? especially how current reach from DC battery to alarm?


Hi,Abebe Alem
It should work well. But I can not confirm. Because I have not actually tried it.
If you can wait My son will create for you.

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