4/7

A HIGH RESOLUTION / PRECISION THERMOMETER USING ST7 AND NE555

5 DESIGN

termine the frequency of the output signal (3).

For the given temperature range (0 - 40 °C) and a 10K

Ω NTC resistor, the chosen values are

40k

Ω for R

Table 1. Table of theoretical values of designed thermometer

Temperature

(°C)

R

t

t

t

∆t

0

27279

4,662

2,772

37299

22176

635

1

26134

4,583

2,772

36665

22176

605

2

25043

4,507

2,772

36060

22176

577

3

24003

4,435

2,772

35483

22176

549

4

23012

4,367

2,772

34934

22176

524

5

22067

4,301

2,772

34410

22176

500

6

21166

4,239

2,772

33910

22176

477

7

20306

4,179

2,772

33434

22176

455

8

19486

4,122

2,772

32979

22176

434

9

18703

4,068

2,772

32545

22176

414

10

17956

4,016

2,772

32131

22176

395

11

17243

3,967

2,772

31736

22176

378

12

16561

3,920

2,772

31357

22176

361

13

15910

3,875

2,772

30997

22176

345

14

15288

3,831

2,772

30652

22176

329

15

14694

3,790

2,772

30322

22176

315

16

14126

3,751

2,772

30007

22176

302

17

13582

3,713

2,772

29706

22176

288

18

13063

3,677

2,772

29418

22176

276

19

12565

3,643

2,772

29142

22176

263

20

12090

3,610

2,772

28879

22176

252

21

11635

3,578

2,772

28626

22176

242

22

11199

3,548

2,772

28385

22176

231

23

10782

3,519

2,772

28154

22176

222

24

10382

3,491

2,772

27932

22176

212

25

10000

3,465

2,772

27720

22176

203

26

9633

3,440

2,772

27517

22176

195

27

9282

3,415

2,772

27322

22176

187

28

8945

3,392

2,772

27135

22176

179

29

8622

3,370

2,772

26956

22176

172

30

8312

3,348

2,772

26784

22176

164

31

8016

3,328

2,772

26620

22176

158

32

7731

3,308

2,772

26462

22176

151

33

7458

3,289

2,772

26311

22176

146

34

7195

3,271

2,772

26165

22176

139