Simple Heat Sensor Circuit Diagram

This simple heat sensor circuit could senses heat from various electronics device like computer, amplifier etc. and generate warning alarm. It could senses heat from environment also, but here I mention “electronics device” because it is being using mostly in electronic device to protect them from overheat. 

Thermistor, 110 Ohms:

Fig-2: 110 Ohms Thermistor

As it is a heat sensor circuit, here a thermistor is used as a heat sensor. It is a thermal measurement device and has a variety of usages including temperature sensor/ heat sensor. The thermistor used in this circuit is a NTC (Negative Temperature Coefficient) type thermistor. When temperature increases, its resistance goes decrease. Therefore, NTC thermistor’s resistances are inverse of temperature.

Circuit Description:

You have seen, in this simple circuit diagram of heat sensor, a few number of components is used including a BC548 transistor, a 110 ohms thermistor etc.

• BC548: BC548 is a TO-92 type NPN transistor, as its alternative you can use 2N2222, BC238, BC548, BC168, BC183 etc. they all have almost same characteristic.
• 110 Ohms Thermistor: A 110 Ohms thermistor is used to detecting heat. I have told already about it.
• Buzzer: A buzzer is used with +9V and collector of transistor. When the temperature/ heat exceeds a certain level then it make an alarm.
• 4.7V Zener diode:  It is used to limit the emitter current of BC548.
• 9V Battery: A 9V battery is used as a single power source.
• R1, R2: A 3.3K 1/4w resistor is used as R1 and 100 ohms 1/4w as R2.
• Switch: Here in this circuit the switch used is a simple SPST switch. You can either use the switch or not, choice is yours. It is not mandatory.

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IC LM35 Temperature Sensor Characteristics

LM 35 temperature sensor IC is a IC chip production Natioanal Semiconductor which serves to determine the temperature of an object or space in the form of electric scale, or can also be defined as an electronic component that is used to change the temperature changes are accepted in the electrical wholesale changes. LM35 temperature sensor IC temperature change can change a change in voltage at the output. LM35 temperature sensor IC requires +5 volts DC source voltage and DC current consumption of 60 mA in operation. Physical form LM 35 temperature sensor is an IC chip with packaging that varies, in general packaging LM35 temperature sensor is packaged TO-92 as shown in the figure below.

IC LM35 Temperature Sensor Characteristics 

From the picture above it can be seen that the temperature sensor IC LM35 basically have 3 pin that serves as a source of supply voltage of +5 volts DC, as a result of sensing the output pin in the form of a change in the DC voltage and Vout pin to Ground.

IC LM35 temperature sensor characteristics are:

•     Temperature sensitivity, with linear scaling factor between voltage and temperature 10 mVolt / º C, so it can be calibrated directly in centigrade.
•     Have the accuracy or the accuracy of the calibration is 0.5 º C at 25 º C.
•     Has a maximum operating temperature range between -55 º C to +150 º C. Working at a voltage of 4 to 30 volts.
•     Has current low at less than 60 mA.
•     Have a low self-heating (low-heating) of less than 0.1 º C in still air.
•     Has a low output impedance is 0.1 W for 1 mA load.
•     have Nonlinearities only about ± ¼ º C.

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Simple Temperature Sensor Circuit Diagram

This is a simple Temperature Sensor Circuit Diagram. The LM35 temperature sensor provides an output of 10 mV/C for every degree Celsius over 0C. At 20C the output voltage is 20 10 = 200 mV. The circuit consumes 00. The load resistance should not be less than 5 kQ. A 4- to 20-V supply can be used.

Temperature Sensor Circuit Diagram

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Temperature Sensor Circuit Diagram

Simple Temperature Sensor Circuit Diagram. The LM35 temperature sensor provides an output of 10 mV/C for every degree Celsius over 0C. At 20C the output voltage is 20 10 = 200 mV. The circuit consumes 00. The load resistance should not be less than 5 kQ. A 4- to 20-V supply can be used.

Simple Temperature Sensor Circuit Diagram

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