M U thut vi iu khin hin nay rt pht trin rt mnh m, n c ng dng vo rt rt nhiu lnh vc t trong i sng sinh hot hng ngy(kha s, t lnh, ti vi, ...) cho ti cc lnh vc trong cng nghip cng nh trong qun s. Do c nhiu u im nh nh gn, kh nng lp trnh iu khin theo mun, gi thnh thp, c kh nng x l c nhiu cng vic ln vi iu khin tr thnh linh kin khng th thiu c trong cc thit b phc v con ngi chng ta. AVR l mt trong rt nhiu dng vi iu khin 8bit hin nay. N c ng dng rng ri trong lnh vc iu khin ng dng, lnh vc iu khin o lng, lnh vc iu khin t ng, lnh vc iu khin qung co .v.v Vi nhng kin thc c c v dng vi iu khin AVR em chn ti tt nghip: Thit k h thng o nhit s dng LM335. Mc tiu ca ti l kt hp vi iu khin AVR kt hp vi IC cm bin nhit thnh h thng o nhit .IC LM335 s cm bin nhit bn ngoi mi trng ( chuyn nhit thnh tn hiu in p) a n vi iu khin AVR x l ri hin th trn LCD 16x2. Ni dung ca n chia lm 3 chng : -, Chng 1: Tm hiu v mt s loi cm bin nhit thng dng v LM335 -, Chng 2: Tm hiu v vi iu khin AVR ,ngn ng C , phn mm WINavr v LCD 16x2. -, Chng 3: Thit k h thng o nhit x dng LM335.

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Chng 1 Tm hiu v mt s loi cm bin thng dng v LM335Trc tin ta cn bit cm bin l g: Cm bin l thit b dng o, m, cm nhn,cc i lng vt l khng in thnh cc tn hiu in. V d: Nhit l 1 i lng khng lin quan n in chng ta phi chuyn n v 1 i lng khc ( in tr, in p ) ph hp vi cc c cu in t. Nguyn l hot ng ca cm bin nhit : Nhit t mi trng s c cm bin hp thu, ti y ty theo c cu ca cm bin s bin i lng nhit ny thnh mt i lng in no ( in p, dng in..). Nh th mt yu t ht sc quan trng l nhit mi trng cn o v nhit cm nhn ca cm bin. C th iu ny l: Cc loi cm bin m ta trng thy n u l ci v bo v, phn t cm bin nm bn trong ci v ny ( bn dn, lng kim.) do vic o c chnh xc hay khng ty thuc vo vic truyn nhit t mi trng vo n phn t cm bin tn tht bao nhiu ( 1 trong nhng yu t quyt nh gi cm bin nhit ). . PHN LOI CM BIN NHIT. Cp nhit in ( Thermocouple ). Nhit in tr ( RTD-resitance temperature detector ) - PT100. Thermistor. Bn dn ( Diode, IC ,.). Ngoi ra cn c loi o nhit khng tip xc ( ha k- Pyrometer ). Dng hng ngoi hay lazer. 1. CP NHIT IN ( Thermocouples ). - Cu to: Gm 2 cht liu kim loi khc nhau, hn dnh mt u. - Nguyn l: Nhit thay i cho ra sc in ng thay i ( mV). - u im: Bn, o nhit cao. - Khuyt im: Nhiu yu t nh hng lm sai s. nhy khng cao. - Thng dng: L nhit, mi trng kht nghit, o nhit nht my nn, - Tm o: -100 D.C