Simple Thermometer Circuit

A thermometer circuit is like a tiny detective for heat.

It uses special sensors to sniff out the temperature and then shows it on a display, like a digital thermometer.

These circuits come in all shapes and sizes, using different ways to sense the temperature.

No matter which kind you use, though they all give you a reading of how hot or cold things are!

Circuit Working:

Parts List:

The provided schematic depicts a digital thermometer circuit utilizing a standard 1N4148 diode as the temperature sensor.

Leveraging the diodes temperature coefficient of -2 mV/°C, this setup achieves precise temperature measurement.

For temperature readout, a digital multimeter is employed, facilitating measurement from -9.99°C to +99.9°C.

Calibrating the digital thermometer involves two steps:

Setting the minimum level 0°C:

• Immerse the diode in a glass of water filled with crushed ice ensuring the waters temperature is verified using a conventional thermometer.
• Adjust P1 until the digital voltmeter reads 000 when the diode detects zero degrees centigrade.

Setting the maximum level 100°C:

• Submerge the diode sensor into boiling water and fine tune P2 until the digital meter precisely displays 99.9.

Formula:

The LM324 is an integrated circuit IC that functions as an operational amplifier, or op amp, and has several uses, such as in circuits for thermometers.

The following basic formula illustrates how the LM324 may be used in a straightforward thermometer circuit:

V_out ​= V_ref​ + K*(V_sensor​ − V_ref​)

where,

• V_out​: Output voltage from the LM324.
• V_ref​: Reference voltage.
• V_sensor​: Voltage from the temperature sensor.
• K: Proportional constant or gain factor of the amplifier circuit inside LM324.

The actual temperature and the reference configuration determine the true voltages, V_sensor and V_ref.

K is determined by the op amp circuitry design within the LM324 as well as the feedback network.

Note:

The idea behind using the LM324 in a thermometer circuit is described in this simple formula.

Specific requirements, such as temperature range, precision, and kind of display or interface used for temperature indication, will determine the actual implementation specifics.

How to Build:

To build the Simple Thermometer Circuit follow the below mentioned steps:

Circuit Assembly Steps:

• Connect the 1N4148 diode to the circuit, across pin 1 and pin 2 of A2.
• Connect pin 3 of A1 to the junction of R1 and R2.
• Connect pin 1 and pin 2 of A1 together.
• Connect P1 preset to pin 3 of A2 .
• Connect pin 3 of A3 to the junction of R6 and R8.
• Connect pin 1 of A2 with pin 2 of A3 through resistor R7.
• Connect resistor R9 between pin 1 and pin 2 of A3.
• Connect pin 1 of A3 with a 100mV meter through the preset P2.
• Connect 9V battery power supply to the circuit through IC1 78L05.

Note:

• Ensure proper polarity and connections are made according to the schematic diagram.
• Once assembled, power the circuit and calibrate it according to the provided calibration instructions.
• The digital multimeter should then accurately display the temperature readings within the specified range.

Conclusion:

To conclude, a thermometer circuit is an electronic system designed to accurately measure and display temperature.

It typically incorporates various temperature sensors signal conditioning components, and a display unit.

These circuits serve a wide range of applications across industries offering precise temperature monitoring for improved process control, environmental observation, medical diagnostics and consumer electronics.

The choice of temperature sensor and circuit design depends on factors such as accuracy requirements, temperature range and the specific needs of the application.

References:

 Circuit Diagram of Digital Thermometer