o nhit dng LM35 kt hp IC ADC0808 vi 80511, Gii thiu chung IC
ADC0808l mt vi mch tch hp c chc nng chuyn i tn hiu tng t sang k
thut s (Analog to Digital Converters), phn gii ca b ADC l 8bit tc n
s chuyn i tn hiu in tng t sang 256 mc in p so vi Vref cp vo b chuyn
i. Cc bn c th xem datasheet ca n trong tp nh km.a) S chn:
ngha cc chn: Cc chn t IN0-IN7 l ng vo analog. Vref+/Vref- l chn
cp p so snh. ALE l chn cho php giao tip T 2-1 n 2-8 l cc ng ra song
song 8bit START l chn cho php chuyn i EOC l chn bo qu trnh chuyn i
hon tt, kiu dng c ngt ADD A, ADD B, ADD C l 3bit a ch chn knh u vo
t IN0-IN7 VCC, GND l chn cp ngun dng 5V v ngun m (Mass) CLOCK l chn
cp xung ng h cho IC hot ng, tc ly mu v chuyn i ph thuc vo ci ny, ti
a 640khz OUTPUT ENABLE (OE) l chn bo cho IC xut data ra Port vi iu
khin ly i.b) Gin xung giao tip IC ADC0808 (ADC0809)
c) Cm bin nhit LM35l cm bin nhit , u ra l tn hiu in p bin i theo
nhit , c 10mV tng ng vi 1 C v gii o ca IC ny l -55 n 150 C, in p
cung cp t 4-20VDC. o c nhit m tc nh hn 0 ta phi cp thm ngun m -Vs
cho IC ny nh sau:
2, Lp trnh giao tip ADC0808Tnh nng: T ng cp nht gi tr ADC (gi tr
nhit ca LM35) t IC ADC0808 ri hin th ln LCD 16x2, to xung ng h cho
IC ADC0808 s dng ngt timer.Xy dng: Xy dng cc hm giao tip LCD v giao
tip ADC0808 c th nh sau* LCD16x2: LCD_Init() Hm khi to LCD
LCD_Clear() Hm xa mn hnh LCD_Gotoxy(X,Y) Hm tr ti v tr trn mn hnh.
Trong X l v tr 0-15, Y l dng 0-1 LCD_PutChar(k_t_ascii) Hm gi mt k
t ASCII ln LCD LCD_Puts(Ni dung) Hm gi mt chui k t ln LCD* ADC0808:
ADC0808_Read(channel) Hm c ADC theo knh t 0-7 V mt s hm khc nh
delay, tnh nhit , chuyn i hin th....CODE://Khai bo chn giao tip
ADC0808#define ADC0808_DATA P3 //PORT#define ADC0808_A P2_0
//PIN#define ADC0808_B P2_1#define ADC0808_C P2_2#define
ADC0808_ALE P2_3#define ADC0808_START P2_4#define ADC0808_EOC
P2_5#define ADC0808_OE P2_6#define ADC0808_CLK P2_7/**********Hm c
ADC0808 theo knh******/unsigned char ADC0808_Read(unsigned char
channel){ unsigned char kq; ADC0808_A = channel & 0x01; //Chn
knh ADC0808_B = channel & 0x02; ADC0808_C = channel & 0x04;
ADC0808_ALE = 1; //Giao tip ADC0808_START = 1; //Bt u chuyn i
ADC0808_ALE = 0; ADC0808_START = 0; while(ADC0808_EOC); //Ch chuyn
i xong while(!ADC0808_EOC); ADC0808_OE = 1; //c d liu kq =
ADC0808_DATA; ADC0808_OE = 0; return kq; //Tr v hm d liu ADC}Xem
code y trong file nh km cui bi vit....!3, M phng trn Proteus:
Ti sao phi to p Vref 2.56V xin c gii thch nh sau: Cng thc tnh in
p chuyn i:Vin = (Vref*ADC)256 Do phn gii ca ADC0808 l 8bit ln s c
256 mc in p so vi Vref. Tc nu ta cp vo Vref l 5V v tn hiu input vo
l 2.5V chng hn th gi tr ADC = 2562 = 128 (do Vin = 12 Vref) t suy
ra Vref = 2.56V th ADC=25 th in p u vo input phi l 250mV => C
tng/gim 10mV l ADC tng/gim 1 gi tr. M cm bin nhit LM35 li c ng ra c
10mV l thay i 1 C nh vy suy ra ADC=25 th LM35 ang 25 C. Vi cch ny
ta khng cn phi tnh ton gi tr nhit sau khi chuyn i m c th xut lun gi
tr ADC ra mn hnh LCD.Lm vi LM35 th vic u tin l bn phi chn c Vref ph
hp v LM35 tng 10mV tng ng vi 1 nn ln n 1o0 mi c 1V nn nu khng chy
Vref ph hp th d vi nhiu nh th sai s cng ln. Thng th dng Vref=2.56V.
Hihi. Mnh cha bit bn ngocanh khng thnh cng im no nn cng cha bit gii
thch g hn.Mnh ch mi lm LM35 vi ATmega8, s dng in p tham chiuVref =
5Vly t bn ngoi. Mun LM35 lm vic n nh th cn thit phi mc thm h thng t
in + cun cm vo 2 chnAVCC, AREF in p chy b chuyn i ADC bn trong v
tham chiu l n nh nht. V ngun cung cp cho ton b mch cng phi cc k n
nh na.
