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.
Resistors (all ¼-watt, ± 5% Carbon)
R1 = 680 Ω
R2 = 1 KΩ
R3, R4, R5 = 1 KΩ
R6 = 6.8 KΩ
R7 = 10 KΩ
VR1 = 2.2 KΩ
VR2, VR3, VR5 = 10 KΩ
C1, C3 = 0.1 µF
C2 = 10 µF/16V
C4 = 10 µF/16V
IC1, IC2 = µA741
D1 = 1N4148 (Sensor)
M1 = 1mA-0-1mA or 0-1mA Ammeter