Door Open Alarm

8/10/2019 Door Open Alarm

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CONSTRUCTION

ELECTRONICS FOR YOU JULY 2003

Fig. 5: Magnet and reedswitch fitted in the door

PRADEEP G.

Commercially available electronic se-curity alarms with remote controlare generally very expensive. Here

is a circuit, with construction details, for alow-cost door-opening alarm with remote

control. However, you need not despair ashere we present a low-cost door openingalarm with remote control. It uses readilyavailable components and is easy to as-

S.C.DW

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CONSTRUCTION

semble.

The circuit

Fig. 1 shows the block diagram of the door-opening alarm with IR remote control. Thecircuit has two main parts, namely, a small

infrared remotetransmitter unit anda receiver unit withalarm.

T r a n s m i t t e r

unit. Fig. 2 showsthe circuit of the re-mote transmitterunit. Its working isvery simple. ICNE555 (IC1) is usedin astablemultivibator modeto operate a fre-quency of 1 kHz. A

pnp transistor (T1) drives the IR LED.Connect a +9V battery to the cir-

cuit. Now on pressing switch S1, the trans-mitter emits a modulated infrared beamup to 7 metres without the need of anylens or reflector.

DOOR-OPENINGALARMWITHREMOTE CONTROL

Fig. 2: Circuit of IR remote transmitter unit

Fig. 4: Circuit of IR receiver unit with alarm

Fig. 3: Bottomview of L14F1

IR photo-transistor

Receiver uni t w ith alarm. The circuitdiagram of the IR receiver unit with alarmis shown in Fig. 4. IR signals sent by thetransmitter are received by Darlington IRphototransistor L14F1 (T2) whose bottomview is shown in Fig. 3. Thusphototransistor T2 is used here as a sen-

sor.As IR signals are very weak, these re-

quire amplification. So the signals are am-plified by the amplifier stage comprisingtransistors T3 and T4. Amplified signalsare fed to the triggering circuit comprisingtransistors T5, T6, and T7 to trigger themonostable multivibrator wired aroundIC2.

W h e nIC2 is trig-gered at pin2, its out-put pin 3goes highfor 5 to 10seconds.Time delaycan be setby a 220kp r e s e t

Fig. 1: Block diagram of door-opening alarm using IR remote control


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CONSTRUCTION

ELECTRONICS FOR YOUJULY 2003

(VR). During this time, transistor T8 con-ducts to keep reset pin 4 of astablemultivibrator IC3 low. Then the alarm getsdisabled.

Within the preset time period if some-body opens the door, i.e. the magnet ismoved away from reed switch S2, pin 4 ofIC3 goes low due to the conduction oftransistor T8 and hence the alarm is notactivated.

After completion of the preset timeperiod if somebody opens the door, reedswitch S2 also gets opened and pin 4 ofIC3 goes high due to non-conduction oftransistor T8 and hence the alarm is acti-vated.

The actual use of the remote controlis that you can disable the alarmwhile you open the door. You can keepthe remote control in your pocket. Whenyou enter the room or go out fromthe room, simply direct remote controlto the sensing phototransistor andmomentarily press switch S1. Thus thealarm is disabled for 5 to 10 seconds.So during this time, you can openthe door without activation of the alarm.After this time duration completes,if anyone tries to open the door, the

alarm will sound.

Assembling

The door opening alarm uses asimple magnet-operated two-leadsreed switch as a sensor. Reed switchS2 is fitted on the door frame usingan adhesive like Feviquick. Themagnet is fitted on the moving partof the door as shown in Fig. 5.

When the door is fully closed,the magnet is close to switch S2 and theinternal leads of the switch get shorted.When the door is opened, the magnetmoves away from the reed switch andhence the internal leads of the reed switchget opened.

Assemble the transmitter unit and thealarm unit on separate PCBs. The PCB of

Fig. 6: Circuit of power supply with battery backup

Fig. 9: Actual-size, single-side PCB for receiver unit

Fig. 10: Component layout of the PCB in Fig. 9

Fig. 7: Actual-size, single-side PCB oftransmitter unit

Fig. 8: Component layout for the PCB in Fig. 7

PARTS LIST

Semiconductors:

IC1-IC3 - NE555 timerT1, T9 - SK100 pnp transistorT2 - IR L14F1 photo DarlingtonT3-T4 - BC549C npn transistorT5 - BC558 pnp transistorT6-T8 - BC548 npn transistorT10 - 2N3054 pnp power transistorIR-LED - LD271 infrared LED

LED - 5mm red LEDD1 - 1N4148 switching diodeD2-D5 -1N4001 rectifier diode

Resistors (al l -watt, 5% carbon,un less stated otherwi se):

R1 - 150-kilo-ohmR2 - 1.5-kilo-ohmR3, R4 - 470-ohmR5 - 4.7-ohmR6, R15, R17,R18, R22, R25 - 10-kilo-ohmR7, R13 - 4.7-kilo-ohmR8 - 470-kilo-ohmR9 - 2.7-kilo-ohmR10, R21, R23 - 1-kilo-ohmR11 - 100-kilo-ohmR12 - 120-ohmR14 - 22-kilo-ohmR16 - 3.3-kilo-ohm

R19 - 680-ohmR20 - 47-kilo-ohmR24 - 2.2-kilo-ohmR26 - 100-ohm, 1WVR -220k preset

Capacitors:

C1, C2, C5, C9,C13, C16 -0.01F ceramic diskC7, C8, C11 - 0.1F ceramic diskC3, C4, C14,C17 - 100F, 25V electrolyticC6 - 47pF ceramic diskC10 - 2.2F, 25V electrolyticC12 - 10F, 25V electrolyticC15 - 0.047F ceramic diskC18 - 1000F, 25V electrolytic

Miscellaneous:

X - 230V AC primary to 12V-0-12V,500mA secondary transformer

S1 - Tactile switchS2 - Reed switchLS1 - 8-ohm, 1W speakerLS2 - 5-ohm, 10W speaker

- Magnet- IC bases- +12V battery- +9Vbattery

the transmitter shouldbe small. All compo-nents, excluding timerIC 555, can be directlysoldered on the PCB.Use 8-pin IC bases fortimer IC. Try to keep

the length of the wirebetween the IRphototransistor and thereceiver PCB as smallas possible. Dont over-heat the sensor whilesoldering. Use a 25Wsoldering iron for sol-dering.

The unit requiresback-up during powersupply failure. There-


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Fig. 11: Power amplifier circuit for loud sound

component layout in Fig. 10.If you want the alarm to sound

loudly during the unauthorised open-ing of the gate, use the power ampli-fier circuit shown in Fig. 11 withanother suitable power supply. Thiscircuit uses another power supply witha 230V AC primary to 12V-0-12V, 2Asecondary transformer and two di-odes of 2A rating (D2 and D3).

fore use a 12V DC power supply withbattery for back-up as shown in Fig. 6.Connect this power supply to the IR re-ceiver unit with alarm.

The actual-size, single-side PCB for thetransmitter circuit (Fig. 2) is shown in Fig.7 and its component layout in Fig. 8. Theactual-size, single-side PCB for the receivercircuit with alarm (Fig. 4) and power sup-ply (Fig. 6) is shown in Fig. 9, and its

AVAILABLE

Complete Kit of Remote-controlled AudioProcessor using Microcontroller

(EFY Sept. 99) for Rs 850/-

KitsnSpares303, Dohil Chambers, 46, Nehru Place, New Delhi 110019Phone: 26430523, 26449577; E-mail: [email protected]

Please add 10% C.S.T. andpostage charges of Rs 50/-

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Door Open Alarm