Electronic Thermometer Circuit

A number of measurement circuits have appeared in this website. The circuit posted here is of thermometer using op-amp 741. This circuit is suitable to measure temperature form 00C to 500C using a linear scale am-meter. The range can be extended up-to 1000C using 100 microampere.

Circuit Description

The circuit is self explanatory for the experienced hobbyist and performs its task with a minimum number of components. The diodes D1 and D2 are use to sense temperature variation while op-amp is used to compare. Capacitor C1 provide noise filtering.

circuit diagram of electronic thermometer

PARTS LIST OF ELECTRONIC THERMOMETER USING OP-AMP 741

Resistor (all ¼-watt, ± 5% Carbon)
R1 = 8.2 KΩR2 = 220 KΩ

R3 = 5.6 KΩ

R4 = 560 KΩ

R5 = 18 KΩ

VR1 = 4.7 KΩ

VR2 = 1 MΩ

Capacitors
C1 = 1 µF/10VC2 = 150 pF

C3, C4 = 100 KpF

Semiconductors
D1, D2 = 1N4148IC1 = 741

IC2 = 7805

Miscellaneous
M1 = 50 µASW1 = ON/OFF Switch

B1 = 9V,PP3 Battery