## 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

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

#### Semiconductors

IC1, IC2 = µA741

D1 = 1N4148 (Sensor)

#### Miscellaneous

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

## 6 thoughts on “Electronics Thermometer”

1. pua chong siang says:

Hi, Sir:
I just want to know what model number of uA741 used in this project because I am doing the same project and want to buy the IC uA741 but I does not know what model of IC uA741.
Thanks you and please kindly info me about the model should be used in this project.
Thanks you very much.

1. Both IC1 and IC2 are UA741 , The general purpose operational amplifier.
Generally you can use any General purpose operational amplifier with numbering 741 from any manufacturer.

2. sotiris says:

I want to ask what range of temperature can it displays and how you can test it? Also you don’t need any probe to touch the human body so to read the temperature?And at last I want to ask you if you use a thermistor instead of D1 do you need to change also the circuit connection to thermistor or you just put it in the same position? Thank you for your time, and I hope to get your answer soon.