Electronics Thermometer:-

Clinical thermometer is only used by doctor because it is difficult to read. Here is a circuit of electronics thermometer used to measure vast range of temperature from -20⁰C to 125⁰C. This single circuit electronics thermometer can be used to measure different temperature. The wide range of temperature measurement made this circuit versatile.

Circuit Description of electronics thermometer

This entire circuit “Electronics thermometer” is built and fabricated around silicon diode D₁ (1N4148) and Operational amplifier IC. Diode D₁ is used as temperature sensor, temperature determined the value of voltmeter drop across diode i.e. at room temperature voltage drop is 0.7V and is reduce by about 2mV/⁰C.

For temperature-to-voltage conversion in electronics thermometer an operational amplifier is used. The input voltage at non-inverting pin 3 of IC₁ is fixed by VR₁, R₁, & R₂ where sensor diode D₁ forms a feedback path. The output of IC₁ is directly depends on the voltage across the diode.

Operational amplifier IC₁ is used as voltage amplifier which amplifier the output from IC₁. Finally, ammeter is used to indicate the temperature.

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R₁ = 680 Ω

R₂ = 1 KΩ

R_3, R₄, R₅ = 1 KΩ

R₆ = 6.8 KΩ

R₇ = 10 KΩ

VR₁ = 2.2 KΩ

VR₂, VR_3, VR₅ = 10 KΩ

Capacitors

C₁, C₃ = 0.1 µF

C₂ = 10 µF/16V

C₄ = 10 µF/16V

Semiconductors

IC₁, IC₂ = µA741

D₁ = 1N4148 (Sensor)

Miscellaneous

                                                           M₁ = 1mA-0-1mA or 0-1mA Ammeter