Digital Design Project

Binary Temperature Monitor

Utilizing

8-Bit A-D

Converter

Denis P. Cote

Binary Temperature Monitor

Overview

Temperature Monitor :

-100º to 90ºC

8 Bit Binary Output

Display (0-255)

Core: ADC0808 8-Bit A/D

IC – National

Semiconductor

A/D Utilizes Successive

Approximation

Single Supply (Vcc)

Referenced to Ground

Conditioned Analog Input:

AD594 Type J

Thermocouple Amp IC

A/D Clocked via 555

Timer Configured as

Astable Multivibrator

Simple Design, Low Cost

& Expandable

Circuit Block Diagram

Voltage

Regulator

(7805)

ADC

0808LED

Output

Resistor

ICAD594

Thermocouple

&

Heat Source

Supply

Voltage

12V

Clock

LM555

Analog In

Digital Out

Vref (+) = 5 Vdc

Vref (-) = GND

Schematic

Model Simulation - MULTISIM

A1

ADC

Vin

Vref+

Vref-

D0

D1

D2

D3

D4

D5

D6

D7SOC

EOCOE

11

U1

DCD_HEX_BLUE

U2

DCD_HEX_BLUE

LED1

A

R2

180 Ω

RP

AC

K 8

17

16

18

19

12

34

56

78

0

A2

555_VIRTUAL

GND

DIS

OUTRST

VCC

THR

CON

TRI

R3100Ω

R4100Ω

VCC

5V

C1100nF

XFC1

123

23

22

0

VCC

14

15

20

21

U5

DC 10MW

3.000 V

+ -0

0

VDD

3V

VDD

VCC

5V

VCC

24

555 Timer Model:

Freq Out - ~29.6KHz

Square Wave at Vcc

Fout =1.44/(R3+2R4)C1

LSB

Analog In Simulation:

Vdd = Output of T/C Amp

Circuit Prototype

Clock Pulse

Freq. ~30KHz

Binary Out:

10010111

Top = MSB

Parts List & CostItem Tag Qty Part No. Vendor Description Unit Price

1 U1 1 ADC0808CCN-

ND

Digi Key / Kit IC ADC 8BIT MPU 8CH MUX 28-DIP $ 5.40

2 U2 1 AD594AQ-ND Digi Key IC THERMOCOUPLE A W/COMP 14CDIP $ 11.48

3 U3 1 LM555CNFS-ND Digi Key IC TIMER SINGLE 0-70DEG C 8-DIP $ 0.44

4 U4 1 NJM78L05A-ND Digi Key 5 Volt Positive Regulator $ 0.12

5 LED 1 67-1009-ND Digi Key LED ARRAY 10X25MM 10SEG RED DIFF $ 2.13

6 TC 1 JMTSS-062G-6 Omega Type J Junction Thermocouple Probe $ 24.95

7 R9 1 Resistor KIT 100 Ohm 1/8 watt carbon film resistor $ -

8 R1-R7 1 Resistor IC KIT 300 Ohm Resistor IC $ -

9 R11 1 Resistor KIT 1K Ohm 1/4 watt resistor $ -

10 R10, R12 1 Trimmer KIT 2K Ohm trimmer potentiometer $ -

11 C1, C3, C4, C5 1 Capacitor Radio Shack 0.1 uF ceramic capacitor $ 1.18

12 C2 1 Capacitor KIT 10 uF 25VDC elecrolytic capacitor $ -

13 D1 1 Rectifier Diode KIT 1N4007 Rectifier Diode $ -

14 S1 1 Dip Switch KIT Dip Switch $ -

Misc Total $ 45.70

Hook Up Wire

breadboard

Measured Performance MultiSIM Model

Vin Binary Out Dec Hex

0 0 0 00

0.500 11001 25 19

1.000 110011 51 33

1.500 1001100 76 4C

2.000 1100110 102 66

2.500 1111111 127 7F

3.000 10011001 153 99

3.500 10110011 179 B3

4.000 11001100 204 CC

4.500 11100110 230 E6

5.000 11111111 255 FF

Sensitivity:

5 volts / 255points =

0.019607 V/Point

~20mV/Point

Error: 1/2 LSB & 1 LSB

Circuit

Vin Vin Actual

Volts Lo Hi Binary Dec Hex

Calculated

Vout Comment

0 0 0.009 0 0 00 0.00

0.500 0.487 0.497 11010 26 1A 0.51

1.000 0.986 1.003 110011 51 33 1.00

1.500 1.479 1.492 1001101 77 4D 1.51

2.000 1.983 2.002 1100110 102 66 2.00

2.500 2.471 2.49 10000000 128 80 2.51

3.000 2.982 3 10011001 153 99 3.00

3.400 3.392 3.404 10101110 174 AE 3.41 (Limit of trimmer pot reached)

0.00

0.00

5.000 5.000 5.010 11111111 255 FF 5.00 Vcc

minmax DD

Dx

VzVfs

Vin

Comparison of

Model

Vs.

Circuit Output

Measured PerformanceADC0808 - Actual Vs Model

Linearity

0102030405060708090

100110120130140150160170180190200210220230240250

0 1 2 3 4 5 6

Input Voltage

Bin

ary

Ou

tpu

t (0

-25

5)

MultiSIM Model

Circuit

Future Improvements

Increase number of Analog Inputs (0-7)

Robust Display: Decimal or Hex

Enable Multiplexing of Inputs

Parallel DIO output to PC – Data Logger

Disadvantages:

– Low Resolution (256 points)

– Limited to Max input equivalent to Vcc

– Higher Resolution = Chip Replacement

Questions/Discussion

Back Up

1 8 15 22 29 5 12 19 26 3 10 17 24 31 7 14 21 28

Project Research (3/10 - 3/30/2008)

Project Selection (3/30/2008)

Project Approval

Design / Model

Part Procurement

Construction

Commission

Final Report Out

8-Bit ADC Digital Design Project (Digital Circuits 2) Project Timeline - 3 month outlook Denis Cote

TaskMarch April May June

ADC0808 Datasheet

Data Sheets:

Analog Devices AD594

LM555 Datasheet

Schedule: