Cảm biến PIR

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.