Cm bin PIR Cho cc bn, Cuc sng ca chng ta tn ti trong cng lc vi nhiu thc th vt l, nhng th chng ta nhn bit c nh l cc vn ng c hc, tc dng ca nhit (nhn bit qua lp da), ca nh sng (nhn bit qua mt), ca m thanh (nhn bit qua tai), ca mi (nhn bit qua mi), ca v (nhn bit qua li), v nht l ca in. Hin nay, in t hc l mt cng c phc v con ngi nhiu nht, chng ta c radio, cassette, TV, my ghi hnh, my tnh....u im ca cc thit b in l x l cc vn rt nhanh, nhng cc thit b in th li ch lm vic vi tn hiu thuc in, m chung quanh chng ta khng phi ch c cc hin tng thuc in m song song cn rt nhiu hin tng phi in khc ang tn ti, t ngi ta ngh n cc SENSOR. Sensor l cc cm bin, n dng chuyn i cc tn hiu khng thuc in ra dng tn hiu in v a vo cc dng mch in x l. Ngy nay c rt nhiu, rt nhiu loi SENSOR. Trong ln ny, chng ta s tm hiu loi sensor dng pht hin cc vt th nng c chuyn ng ngang, quen gi l PIR moton detector.

PIR l g?N l ch vit tt ca Passive InfraRed sensor (PIR sensor), tc l b cm bin th ng dng ngun kch thch l tia hng ngoi. Tia hng ngoi (IR) chnh l cc tia nhit pht ra t cc vt th nng. Trong cc c th sng, trong chng ta lun c thn nhit (thng thng l 37 C), v t c th chng ta s lun pht ra cc tia nhit, hay cn gi l cc tia hng ngoi, ngi ta s dng mt t bo in chuyn i tia nhit ra dng tn hiu in v nh m c th lm ra cm bin pht hin cc vt th nng ang chuyn ng. Cm bin ny gi l th ng v n khng dng ngun nhit t pht (lm ngun tch cc, hay ch ng) m ch ph thuc vo cc ngun tha nhit, l thn nhit ca cc thc th khc, nh con ngi con vt... Trc ht, chng ta tm hiu cu trc ca mt cm bin PIR (Bn xem hnh).

Trn y l u d PIR, loi bn trong gn 2 cm bin tia nhit, n c 3 chn ra, mt chn ni masse, mt chn ni vi ngun volt DC, mc p lm vic c th t 3 n 15V. Gc d ln. tng nhy cho u d, Bn dng knh Fresnel, n c thit k cho loi u c 2 cm bin, gc d ln, c tc dng ngn tia t ngoi. Hnh v cho thy cch dng u d PIR pht hin ngi hay con vt di chuyn ngang.

Nguyn l lm vic ca loi u d PIR nh hnh sau: Cc ngun nhit (vi ngi v con vt l ngun thn nhit) u pht ra tia hng ngoi, qua knh Fresnel, qua kch lc ly tia hng ngoi, n c cho tiu t trn 2 cm bin hng ngoi gn trong u d, v to ra in p c khuch i vi transistor FET. Khi c mt vt nng i ngang qua, t 2 cm bin ny s cho xut hin 2 tn hiu v tn hiu ny s c khuch i c bin cao v a vo mch so p tc ng vo mt thit b iu khin hay bo ng.

Hnh v cho thy 2 vng cm ng nhy cm tng ng vi 2 cm bin trong u d. Khi c mt con vt i ngang, t thn con vt s lun pht ra tia nhit, n c tiu t mnh vi knh Fresnel v ri tiu t trn bia l cm bin hng ngoi, vy khi con vt i ngang, ng ra ca u d chng ta s thy. xut hin mt tn hiu, tn hiu ny s c cho vo mch x l to tc dng iu khin hay bo ng. Bn xem hnh ng sau y dng din t nguyn l lm vic ca u d PIR i vi ngi qua li:

L thuyt chung v tia nhit:

Mi vt th u c cu to t cc phn t nh li ti, nhit l mt dng nng lng to ra t cc xao ng ca cc phn t (Bn xem hnh), l cc chuyn ng hn lon, khng trt t. T cc xao ng ny, n pht ra cc tia nhit, bng cm gic thng thng ca gic quan, con ngi chng ta ni l sc nng. mi ngi ngun thn nhit thng c iu n mc 37 C, l ngun nhit m ai cng c v nu dng linh kin cm ng thn nhit, chng ta s c thit b pht hin ra ngi, chnh l tng m ngi ta ch ra thit b motion detector, iu khin theo ngun thn nhit chuyn ng. Hnh v sau y cho thy vt liu nhm pyroelectric c dng lm cm bin d tia nhit.

Ngi ta kp vt liu pyroelectric gia 2 bn cc, khi c tc kch ca cc tia nhit, trn hai 2 bn cc s xut hiu tn hiu in, do tn hiu yu nn cn mch khuch i. Trong b u d PIR, ngi ta gn 2 cm ng PIR nm ngang, v cho ni vo cc Gate (chn Cng) ca mt transistor FET c tnh khuch i. Khi cm bin pyroelectric th nht nhn c tia nhit, n s pht ra tn hiu v khi ngun nng di chuyn ngang, s n cm bin pyroelectric th hai nhn c tia nhit v n li pht ra tn hiu in. S xut hin ca 2 tn hiu ny cho nhn bit l c mt ngun nhit di ng ngang v mch in t s pht ra tn hiu iu khin. Tn hiu ny c th dng tt m n hay dng bo ng khi c k l vo nh. By gi hy ni n thit b tiu t gm tia nhit ri trn b mt cm ng PIR: Chng ta bit cc tia nhit pht ra t thn th ngi rt yu v rt phn tn, tng nhy phi dng knh c mt knh li to chc nng tiu t, quen gi l kinh Focus, hnh ng di y cho thy cc mt sng ca cc tia sng khi i qua mt mt knh li c cho gm li ti mt im nh, im gi l tiu im ( theo m Hn Vit, ch tiu bn di c b ha , vy n c ngha l im nng, nhiu Bn dng knh lp to ra im nng, im nng ny c th t chy giy y, l tr chi ca cc bn nh).

Khuyt im ca loi knh hi t dng mt li thng thng l khi mt knh m rng, im tiu t s khng nm mt ch, ngi ta cho hiu chnh sai lch ny bng mt knh Fresnel (Bn xem hnh, cc mt cong xa trc quang c chnh li). Bn thy khi xa trc quang hc, cong ca mt knh c hiu chnh li, vi cch lm ny, chng ta s c th hi t nhiu tia sng tt hn, trn mt din tch rng ln hn v nh vy s tng c nhy cao hn v c gc d rng hn. Tm hiu knh Fresnel.

hiu r hn v cch tiu t dng knh Fresnel, Bn c th xem video di y, T gii thch qua on phim ngn ny, Bn s thy knh Fresnel to tnh tiu t tt hn loi knh li thng thng nht l khi m rng mt knh. Mt s mch in in hnh: Sau y l mt s in hnh cho thy cch kt hp gia u d PIR v mch khuch i, mch so p (dng ic LM324) v mch to tr (dng ic logic CD4538) c cc tip im l kim (ca mt relay) dng iu khin cc dng c in khc.

Phn tch s mch in: S cho thy, b u do PIR c 3 chn, chn 3 cho ni masse, chn 1 ni vo ng ngun v chn 2 cho xut ra tn hiu, nguyn do phi phn cc cho u PIR l v bn trong n c dng transistor FET. R2 (100K) l in tr ly tn hiu. Tn hiu ny cho qua 2 tng khuch i vi IC1A v IC2B. y, ngi ta dng mch hi tip nghch vi R4 (1M), R3 (10K) v t C2 (10uF) nh li cho tng khuch i ny (do 1M/10K = 100, nn li tng ny ly khong 100), t C3 (0.1uF) c tc dng p dy tn hp li, ch cho lm vic vng tn thp b vng tn cao (v tc nhn nhit c qun tnh ln, thng thay i rt chm), tn hiu ly ra trn chn 1 cho qua in tr gim bin R5 (10K) v t lin lc C4 (10uF) vo tng khuch i sau trn chn s 6. Mch dng in tr R6 (1M), diode D1, D2 v in tr R7 (1M) to thnh cu chia p, n ly p phn cc cho chn 5 ca tng khuch i v to in p mu (Vref) cp cho chn 9 (ng vo o) v chn 12 (ng vo khng o) ca 2 tng so p IC1C v IC1D. in tr R8 (1M) v t C5 (0.1uF) to tc dng hi tip nghch, n nh cho tng khuch i IC1B. Tn hiu cm bin sau khi c khuch i cho ra trn chn 7, ri cng lc a vo 2 tng so p trn chn 10 v chn 13. y l 2 tng so p c chu trnh hi sai, dng to ra xung kch thch c dc tt, kch vo tng a hi n n trong ic CD4538, diode D3 v diode D4 c cng dng cch ly trnh nh hng qua li ca 2 ng ra trn chn 8 v chn 14. CD 4538 l ic logic c 2 tng n n, n nh thi gian qu (thi gian tr) theo thi hng ca in tr R10 (1M) v t C6 (1uF) trn chn s 2. Xung lm chuyn trng thi a vo trn chn 4, khi chuyn mch mc p cao cho xut hin trn chn s 6, n s kch dn transistor thc Q1, v Q1 cp dng cho relay ng cc tip im l kim. Do dng mch n n, nh thi theo thi hng ca R10 v t C6, nn ch sau mt thi gian qui nh, mch s t tr li trng thi n c, Q1 s tt v relay s b ct dng v nh tip im l kim ra

Mch c th lm vic vi mc ngun nui t 5 n 12V (Bn ch mc ngun nui chn loi relay cho thch hp). Tm li, khi c ngi i ngang qua b u d, ngun thn nhit ca ngi hay con vt s tc kch vo u d PIR, th relay s c cp dng ng cc tip im l kim, Bn c th dng cc tip im ny m n, v sau mt lc mch n n tr v trng thi vn c v n s t tt. Chng ta c mch tt m n theo "hi ngi qua li" ri phi khng? Thch khng? T liu v 2 ic LM324 v CD4538 dng trong mch:

Trong ic LM324 c 4 tng khuch i ton thut (op-amp), Bn c th dng cc tng khuch i op-amp ny khuch i cc tn hiu hay dng lm tng so p. y l ic c rt nhiu cng dng, Bn ti t liu lin quan phn mc download hiu r hn.

y l ic c 2 b a hi n n, thi gian qu c th xc nh theo mch thi hng vi in tr v t in. Mch s t tr li trng thi n c sau thi gian qui nh. IC ny rt thng dng trong cc mch iu khin.

Cc s mch in tham kho:Sau y l cc s tham kho (ti su tm t trn mng), trong cc s ny, b u d PIR dng pht hin chuyn ng ca cc ngun thn nhit ca ngi v con vt v cho xut tn hiu ng m n hay mch bo ng, nguyn l lm vic cng tng t nh mch in in hnh phn tch phn trn.. Mch 1: Mch dng ic KC778B chuyn dng cho u d cm bin PIR, dng lm mch t tt m n theo hi ngi, lm vic trc tip vi ngun in AC, cho gim p bng t v tt m n bng TRIAC,

Mch 2: Mch dng ic KC778B chuyn dng cho u d cm bin PIR, dng lm mch t tt m ntheo hi ngi, lm vic trc tip vi ngun in AC, cho gim p bng t v tt m n bng tip im ca relay,

Mch 3: Mch dng ic KC778B chuyn dng cho u d cm bin PIR, dng lm mch t tt m ntheo hi ngi, lm vic trc tip vi ngun in DC (12V), tt m n bng relay v c trang b quang tr (SCd) mch ch tc dng trong m ti,

Mch 4: Mch dng ic HT7601A chuyn dng cho u d cm bin PIR, dng lm mch t tt m ntheo hi ngi, lm vic trc tip vi ngun in AC, cho gim p bng t v tt m n bng relay.

Mch 5: Mch dng ic HT7601B chuyn dng cho u d cm bin PIR, dng lm mch t tt m ntheo hi ngi, lm vic trc tip vi ngun in AC, cho gim p bng t v tt m n bng TRIAC,

Mch 6: Mch dng ic KC778B chuyn dng cho u d cm bin PIR, dng pht hin ngi theothn nhit, dng iu khin vi cc loi thit b cm l OUTPUT, lm vic vi ngun in DC, c dng quang tr (SCd) mch ch c tc dng trong m ti.

Mch 7: Mch tt m n theo hi ngi dng u d PIR, v tt m n vi TRIAC, mch dng trctip ng ngun AC v cho gim p bng t.