A number of measurement circuits have appeared on this website. The project posted here is of Electronic Thermometer Circuit using op-amp 741. This circuit is suitable to measure temperature from 00C to 500C using a linear scale am-meter. The range can be extended up to 1000C using 100 microamperes.
Circuit Description of Electronic Thermometer Circuit using 741 IC
The circuit is self-explanatory for the experienced hobbyist and performs its task with a minimum number of components. The operational amplifier is used in compactor mode. The diodes D1 and D2 are used to sense temperature variation while op-amp is used to compare. Capacitor C1 provides noise filtering.
Check out other Electronics Thermometer and Temperature related circuits posted in bestengineeringprojects.com
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- Electronic Room Thermometer Using Op-amp 741
- PIC16F73 Based Temperature Indicator and Controller
- Dynamic Temperature Indicator and Controller Using Ardunio
PARTS LIST OF ELECTRONIC THERMOMETER CIRCUIT USING OP-AMP 741
| Resistor (all ¼-watt, ± 5% Carbon) |
| R1 = 8.2 KΩ
R2 = 220 KΩ R3 = 5.6 KΩ R4 = 560 KΩ R5 = 18 KΩ VR1 = 4.7 KΩ VR2 = 1 MΩ |
| Capacitors |
| C1 = 1 µF, 10V (Electrolytic Capacitor)
C2 = 150 pF (Ceramic Disc) C3, C4 = 100 KpF (Ceramic Disc) |
| Semiconductors |
| D1, D2 = 1N4148 (silicon switching signal diode)
IC1 = 741 (General Purpose Operational Amplifier IC) IC2 = 7805 (5 Volt fixed series voltage regulator) |
| Miscellaneous |
| M1 = 50 µA
SW1 = ON/OFF Switch B1 = 9V,PP3 Battery |
Kindly plz tell me how this therometer works i made it but my am.meter showing 80-90 micro ampere
can u tell me what is C3,C4=100KpF means?
it’s value of capacitors c3 and c4.
100Kpf = 100000 pF = 100 nano farad = 0.1 microfarad.
In the VR1 and VR2, can we use RM-065 4.7k and 1M ohm?
https://uploads.disquscdn.com/images/cc29ae9022087235295f36832b3b32056ec04ea2dd9872e2ea77c6df006ce219.jpg
Is the output correct? the current range?
What is output we should get finally?
R1, R2, D1 and C1 should be connected together.
There is no connection between r1 and r2.
Resistor R2 is connected in series with capacitor c1 and further connected to cathode of diode D2.