electrònica digital temperature measurement...

Electrònica Digital

Temperature Measurement System

Grup de classe: 1BT5 Grup de treball Nº: 3 Autors: Andreas Eder, Mario Faschang, Christoph Hangweirer and Franz Peter Musil Data: 09.06.2009

Electrònica Digital


Andreas Eder, Mario Faschang, Christoph Hangweirer and Franz Peter Musil


Andreas Eder, Mario Faschang, Christoph Hangweirer and Franz Peter Musil


2

Abstract:

Many methods have been developed for measuring temperature. Most of these rely on measuring some

physical properties of a working material that varies with temperature. So this change has to be

transformed to an electrical signal and afterwards processed to visualize at a 7 segment display.

Table of contents:

1 Introduction and Specification............................................................................ 3

1.1 Introduction ................................................................................................................................ 3

1.2 Specification and bloc diagrams ................................................................................................. 3

2 System design ..................................................................................................... 4

2.1 The Converter / Input Circuit ..................................................................................................... 4

2.2 ADC – Analog Digital Converter ............................................................................................... 6

2.3 Sequential System to Control AD Conversion ........................................................................... 7

2.4 12 bit D-Latch ............................................................................................................................ 9

2.5 Converter Block.......................................................................................................................... 9

2.6 BIN to BCD Converter ............................................................................................................. 10

2.7 Quadruple BCD to 7 Segment Converter ................................................................................. 11

3 Conclusions and Bibliography.......................................................................... 13

3.1 Conclusions .............................................................................................................................. 13

3.2 Bibliography ............................................................................................................................. 13

3

1 Introduction and Specification

1.1 Introduction

We use a PT100 to measure the temperature. Our PT100 has a temperature range from 0°C to 100°C. The

PT100 changes his resistance from 100Ω to 138.5 Ω. For each 1°C the resistance changes his value by 0.4

Ω. This resistance will be changed by the transducer into a voltage range of 0 V to 10 V. Then this

Voltage is converted into Binary values by an AD-Converter. Afterwards the Binary values are

transformed into BCD Code. Then this code is converted to control the 7 segment displays. We use four 7

segment displays to show the temperature with one decimal place.

1.2 Specification and bloc diagrams

The main part of our project is shown above and the inner part you can see in the circuit below.

The detailed description you can read in the following points.


4

2 System design

2.1 The Converter / Input Circuit

The PT100 is connected to the SENS_PLUS and SENS_MIN Port.

The INPUT_CIRC consists of a “Wheatstone Bridge” and an “Instrumentation amplifier”. The output of

this bridge dV goes to two amplifiers (OPV 1 and OPV2). The outputs of these amplifiers are combined

in a final amplifier (OPV 3).

Calculation of R1

R1 specified the current through the PT100 which should be about 1mA. The whole circuit is supplied

with 12 Volts (VCC). The PT100 has 138.5 Ω at 100°C and therefore the voltage at the PT100 is 138.5

mV. The difference between 12 V and 138.5 mV is the voltage at the resistor R1. We can simplify the

calculation and so we get for the value of R1:

12 1 12Ω

Calculation of R2

The resistor R2 should be approximately the same as R1. So we select for R2:

10Ω

Calculation of R3

The voltage dV is zero, if

. So we get for R3:

83.33Ω

Because of the nonlinear behavior of the PT100, we changed the value of R3:

116.25Ω

Calculation of R5,R6, R7, R8, R9, R10

INPUT_CIRC

CCT006

OSENS_MIN

VCC

GND

SENS_PLUS

VCC

VCC

R112k

R210k

R4220k

R5616

R6220k

R7

10k

R9

10k

R8

10k

R10

10k

+88.8Volts

O

VCC

VCC

VCC

3

21

411

OPV1

LM324

3

21

411

OPV2

LM324

3

21

411

OPV3

LM324

VDD

+88.8

Volts

VCC

+88.8

Volts

VDD

VDD

R3116.25

+88.8

mA

SENS_PLUS

SENS_MIN

O

+88.8

mV

DV

Wheatstone bridge Instrumentation amplifier

dV

Rv = PT100 Resistance

5

With those values 0 if the temperature is 0°C and 14 if the temperature is 100°C. For

all other temperatures we can calculate dV by:

! R7, R8, R9, R10 should be a symmetrical voltage divider, so the values of those resistances are all the same.

We choose

" # $ % 10Ω

We want to use the maximum range of 0V – 10V of the ADC so we have to gain dV. Therefore we need a

gain of:

1014 714.286

To simplify the calculation we set R4 and R6 to:

' ( 220Ω

The gain of the amplifier can be calculated by:

)1 2 '*

+ )#"

+ and so we get for R5:

* 2 ' 1 616.86 Ω


6

2.2 ADC – Analog Digital Converter

We use a 12 Bit parallel AD converter AD1674. You can choose between a unipolar and a bipolar input

range. We used the unipolar input range from 0V – 10V.

ADC

CCT007

VIN D[11..0]

CLK

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

D0

D1

D2

D3

D4

D5

D6

D7

D8

D9

D10

D11

CLK

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

D[11..0]

+88.8Volts

?

12/8 2

CS 3

A0 4

CE 6

R/C 5

REFOUT8

REFIN10

20VIN14

10VIN13

AGND9

STS 28

DB11 27DB10 26

DB9 25DB8 24DB7 23DB6 22DB5 21DB4 20DB3 19DB2

18DB1 17DB0 16VAS

7

VEE

11

BIPOFF12

U1

AD1674

? ? ? ? ? ? ? ? ? ? ? ?VCC

VDD

?

CLK

VIN

?

7

2.3 Sequential System to Control AD Conversion

We designed a sequential system to control the AD Conversion.

When AD is “1” the AD Converter is stared to convert, when DLatch is “1” the D-Latch is set to store the

Data.

The sequential system is controlled by the clock and we use the following truth table for creating the CC1

circuit.

S1 S0 S1

+ S0

+

0 0 0 1

0 1 1 0

1 0 1 1

1 1 0 0

From this we get the expressions: S0+ = S0’

S1+ = S1’ S0 + S1 S0’

For creating CC2 we got the truth table below.

S1 S0 AD DLatch

0 0 0 0

0 1 1 0

1 0 1 1

1 1 1 0

With the expressions: AD = S0 + S1

DLatch = S1 S0’

AD = 0

DLatch = 0

S3

AD = 1

DLatch = 0

AD = 1

DLatch = 1

AD = 1

DLatch = 0

S2

S1

S0


8

Our designed Sequential System

9

2.4 12 bit D-Latch

This 12 bit D-Latch is controlled by the previous Sequential System.

2.5 Converter Block

In the converter block we convert the digital data to the right temperature range. We get values from 0 to

4096. We divide the input data by 4 (only cancel the last two bits) so we get values from 0 to 1024. This

data are converted to BCD.

CONVTOBCD[0..3]

CONVTOBCDC[0..3]

CONVTOBCDB[0..3]

CONVTOBCDA[0..3]DD[11..0]

CONV

CCT008

DINCONV[11..0]

HBCDOUT[3..0]

ZBCDOUT[3..0]

EBCDOUT[3..0]

DBCDOUT[3..0]


10

2.6 BIN to BCD Converter

We use this block to convert the binary number to a BCD number. We used the combinational circuit

from the class 2 years before (Exercise 4) http://epsc.upc.edu/projectes/ed/ED/grups_classe/07-08-

q2/1BM2/07-08-Q2-1BM2.htm . Here is also the link to the Proteus file:

http://epsc.upc.edu/projectes/ed/ED/grups_classe/07-08-

q2/1BM2/EX/EX4/est/G7_EX4_Conversor%2016%20bits.DSN

HB

CD

OU

T[3

..0]

EB

CD

OU

T[3

..0]

ZB

CD

OU

T[3

..0] DBCDOUT[3..0]

RE

SIN

BIN

[13.

.0]

RESINBIN9

RESINBIN8

RESINBIN7

RESINBIN6

RESINBIN5

RESINBIN4

RESINBIN3

RESINBIN2

RESINBIN1

RESINBIN10

RESINBIN13

RESINBIN12

RESINBIN11

RESINBIN0

DB

CD

OU

T3

DB

CD

OU

T2

DB

CD

OU

T1

DB

CD

OU

T0

ZB

CD

OU

T0

ZB

CD

OU

T1

ZB

CD

OU

T2

ZB

CD

OU

T3

EB

CD

OU

T3

EB

CD

OU

T2

EB

CD

OU

T1

EB

CD

OU

T0

HB

CD

OU

T0

HB

CD

OU

T1

HB

CD

OU

T2

HB

CD

OU

T3

DINCONV2

DINCONV3

DINCONV4

DINCONV5

DINCONV6

DINCONV7

DINCONV8

DINCONV9

DINCONV10

DINCONV11

DINCONV1

DINCONV0

DBCDOUT[3..0]

EBCDOUT[3..0]

ZBCDOUT[3..0]

HBCDOUT[0..3]

BIN-BCD

BIN-BCD

RES[13..0]

RESTH[3..0]RESH[3..0]

REST[3..0]RESU[3..0]

0 1 1 1 1 0XCVGFHZGNJZUMK

10 0 0

0010

0001

0

00

1

0000

BIN-BCD

BIN-BCD

RES[13..0]

RESTH[3..0]RESH[3..0]

REST[3..0]RESU[3..0]

11

2.7 Quadruple BCD to 7 Segment Converter

The four inputs(BCDINA[0..3], BCDINB[0..3], BCDINC[0..3], BCDIND[0..3]) are each 4-Bit BCD

coded Buses. Each input is for controlling the corresponding “7 segment” display. For this the four

outputs (7segA[0..7], 7segB[0..7], 7segC[0..7], 7segC[0..7]) are used. Each output is a Bus with 8 lines (7

for the segment and one for the dot). The whole display for the temperature consists of four red, 1 digit,

Common Cathode, 7 segment displays.

The inner part of the 4BCD-7SEG is shown below.

RE

ST

H[3

..0]

B[1

3..0

]

RESU1

RESU2

RESU3

REST3

REST0REST1

REST2

RESH3

RESH0

RESH2

RESH1

RESTH0

RESTH2

RESTH3

B0

B1

B2

B3

B4

B5

B6

B7

B8

B9

B10

B11

B12

B13

B14

B15

RESTH1

RESU0

DM74185

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

RES[13..0]

DM74185/2

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

DM74185/4

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

DM74185/3

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

DM74185/6

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

DM74185/5

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

DM74185/9

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

DM74185/8

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

DM74185/7

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

DM74185/12

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

DM74185/11

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

DM74185/10

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

DM74185/15

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

DM74185/14

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

DM74185/13

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

DM74185/16

CCT003

E

D

C

B

A

Y8

Y7

Y6

Y5

Y4

Y3

Y2

Y1

RESU[3..0]

REST[3..0]

RESH[3..0]

RESTH[3..0]

U20

BUFFER

? ? ? ?? ? ? ? ? ? ? ? ? ? ? ?

?


12

We used the Binary to 7 Segment Circuit from the Electronica Digital Homepage:

http://epsc.upc.edu/projectes/ed/ED/unitats/unitat_2_11/Unitat_2_11.htm

In this circuit a memory is used to control the 7 Segment Display. More Information can be found in the

Web.

The outputs 7SEGA7, 7SEGB7, 7SEGC7, 7SEGD7 are used for displaying the dot in the “7 segments”.

Only the B display needs a dot and so the value of 7SEGB7 is “1”.

13

3 Conclusions and Bibliography

3.1 Conclusions

The Converter / Input circuit has some weak points. If R4, R5, R6 are heated, the resistance will change

and so the gain of the amplifiers will change too and a little error occurs at the output.

To minimize this error, the resistance should be of the same material.

It is really difficult to simulate the whole circuit in Proteus. Often we had a problem with the timing. So

we added a canonical system, which controls the whole conversation process.

3.2 Bibliography

[1] Tietze, Ulrich, “Electronic circuits: handbook for design and application” 2nd ed., Springer

Verlag, 2007

[2] Pàgina web d’Electrònica Digital, Binary to 7 Segment Circuit

http://epsc.upc.edu/projectes/ed/ED/unitats/unitat_2_11/Unitat_2_11.htm

[3] Pàgina web d’Electrònica Digital, BIN to BCD Converter

http://epsc.upc.edu/projectes/ed/ED/grups_classe/07-08-q2/1BM2/07-08-Q2-1BM2.htm

electrònica digital temperature measurement...

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