8/6/2019 Atmaga8 + LM335

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o nhit bng LM335 + atmega8 : (S ct bt nhng chi tit khng lin quan ti cng

vic ca bn) S chy tht v nhit o v cng tm n:

1

1

2

2

3

3

4

4

D D

C C

B B

A A

Title

Number RevisionSize

A4

Date: 6/8/2010 Sheet of File: D:\MY WORK\..\TONGHOP.SchDoc Drawn By:

V+

2

ADJ

1

V-

3

U1

LM335Z

330R1

100pF

C1104

VCC

AD0

Rv110K

C1+1

VS+2

C1-3

C2+4

C2-5

VS-6

T2OUT7

R2IN8

R2OUT9

T2IN10

T1IN11

R1OUT12

R1IN13

T1OUT14

GND15

VCC16

U2

MAX232N

X18MHZ

1

2

3

4

5

6

7

8

9

11

10

J1

10uF/16VC5

10uF/16V

C2

10uF/16V

C3

10uF/16VC4

VCC

104

C6

D0

D1

X11

X22

VBAT3

GND4

SDA5

SCL6

SQW/OUT7

VCC8

U3

DS1307

33pFC7

33pFC8

1 2Y2

32.768kHz

VCC

12

P1

PIN DS1307

SCLSDA

VCC

10KR2

10KR3

PC6 (RESET)1

PD0 (RXD)2

PD1 (TXD)3

PD2 (INT0)4

PD3 (INT1)5

PD4 (XCK/T0)6

VCC7

GND8

PB6 (XTAL1/TOSC1)9

PB7 (XTAL2/TOSC2)10

PD5 (T1)11

PD6 (AIN0)12

PD7 (AIN1)13

PB0 (ICP)14

PB1 (OC1A)15

PB2 (SS/OC1B)16

PB3 (MOSI/OC2)17

PB4 (MISO)18

PB5 (SCK)19

AVCC20

AREF21

GND22

PC0 (ADC0)23

PC1 (ADC1)24

PC2 (ADC2)25

PC3 (ADC3)26

PC4 (ADC4/SDA)27

PC5 (ADC5/SCL)28

U4

ATmega8-16PC33pF

C9

33pF

C10XTAL1

XTAL2

XTAL1XTAL2

12

P2

NGUON 5V

D1

D2

104C11

VCC

GND

100uF/16V

C12

1 2

4 3

S1

RESET

RESET

AD0

D0D1

SCLSDA

VCCVCC

SCKMISOMOSI

INT0

INT0

STB

OEDATCLK

VCC

VCC

10KR4

X1X2

X1

X2

H1. LM335 v RS232 hay hin th Led 7 thanh.

Ti a ra cng thc tnh nhit l C :

adc = read_adc(0); // adc l gi tr c v t knh AD0 10bit

T = (adc-558.5)/2.049; //l nhit chuyn i ra C. (1)

By gi ta i gii thch cc thng s : 558.5 v 2.048 u ra.

- ADC ca atmega8 s dng 10bit.

- LM335 l sensor o nhit u ra l 10mV/K.

Mun o C th cn phi chuyn i t K sang C.

Vi ADC 10bit th t 0-5V c v tng ng 0-1023 gi tr ADC. Chn Vref = 5V.

8/6/2019 Atmaga8 + LM335

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Suy ra: ti 0C hay 273K th u vo b AD0 l 2.73V(do 10mV/K).

Nn tnh ra C th phi tr i mc in p l 2.73V tng ng vi gi tr ca ADC 10bit l :

(2.73/5)*1023 = 558.5 gi tr ADC 10bit. Nn trong cng thc (1) xut hin hiu s : adc 558.5

- Khi bn c ADC v th :

Vi Vref = Vcc = 5V nn 1 gi tr tng ng ca ADC 10bit = 5/1023 ~ 0.00488 (V) ~ 4.88

(mV).

Do LM335 c t l :

10mV tng ng thay i 1K

4.88mV ADC c v thay i 0.488K(t l thui m).

Khi cng thc cui cng s l :

T = (adc 558.5) * (4.88mV/10mV) = (adc 558.5) /2.049

Phn cn li l hin th ln Led7 thanh hay giao din trn my tnh ty bn.

Chc thnh cng!