Automatic Room-lock and Lights circuit

dIy: circuit

Automatic Room-lock and Lights circuit mon-anode 7-segment display LTS542 (DIS1). S1 and S2 are o e foot switches. S1 is installed his circuit counts and sani th under door-mat of the door indicates up to nine used to enter the room, and S2 persons present in the is installed under a door-mat room and automatically locks just inside the room. the door and switches off lights as The outputs of IC3 change state synsoon as they leave. It automatically chronously with the low-to-high transiswitches on the lights when the first tions on the clock inputs. Separate count person enters the room. The circuit can up (CPU) and count down (CPD) pins be used as a power-saving device and of IC3 are used here. Its parallel pin 11 a security device to prevent unauthoris made high and parallel data input ised entry in the room, especially in a pins 15, 1, 10 and 9, along with master business meeting room. reset pin 14, are made low in this circuit. Circuit and working The outputs (Q0 through Q3) of IC3 are given to IC4 to drive display The circuit, shown in Fig. 1, is built DIS1. Resistor R11 is used to limit the around three NE555 timer ICs (IC1, IC2 current flowing through DIS1. and IC6), an up/down BCD decade outputs of IC3 are also given to counter 74LS192 (IC3), a 7-segment IC5. output O1 of IC5 is fed to relaydisplay driver 74LS47 (IC4), 4-input driver transistor T3 through resistor NOR gate HEF4002B (IC5) and a comSuresh Dwivedi

T

+ _

CON1 5V

C7 470u 16V

TP1 R12 47K

R13 10K

7 DIS 6

2

S3 LOCK OPEN

S4 LOCK OPEN

C5 220u

1

TH

RESET 4 Vcc 8

IC6 NE555

TRI

GND

5

CV

C6 0.01u

16V

R1 47K

R2 10K

R3 10K

7 DIS 6

2

TH

RESET 4

IC1 NE555

R6 10K

2

S2 DN COUNT

1

C3 100u 16V

13

TCD

1

CPU

PL

IC3 74LS192

CPD P1

Q0

3

Q1

2

Q2

6

Q3

7

P0

15

GND P3 P2 MR 8

9

10

2

I1

3

I2

4

I3

5

I4

14

R7 10K

7 DIS

TH

TCU

T1 BC547

C2 0.01u

6

12

R14 1K

11

Vcc

4

R4 1K

5

CV

C1 100u 16V

16

5

O/P 3

TRI

S1 UP COUNT 1 GND

R5 47K

TP2

Vcc 8

TP6

O/P 3

RESET 4 Vcc 8

IC2 NE555

TRI

GND

TP3

O/P 3 CV

C4 0.01u

5

R8 1K T2 BC547

Vcc NC

IC5

O1

HEF4002B

9

I5

10

I6

11

I7

NC

12

I8

GND

O2

Test Points Test point

Details

TP0 0V, GND TP1 +5V TP2 Low for around 5 seconds when switch S1 is pressed momentarily TP3 Low for around 5 seconds when switch S2 is pressed momentarily TP4 High and light is off. Display shows ‘0,’ means room is vacant TP5 High and door is locked. Display shows ‘0,’ means room is vacant TP6 High for around 11 seconds when switches S3 and S4 are momenta rily pressed simultaneously. Also lock remains open for 11 seconds

R9 to energise relay RL1. Light switches off when RL1 is energised. The second output O2 is fed to relay-driver transistor T4 to energise relay RL2 for locking the door. RL1 and RL2 energise simultaneously as inputs of 4-input NOR gate (IC5) are connected to R15 both the drivers. 1K output O2 of R16 IC5 is also giv1K en to the base T6 T7 of transistor T7 T5 BC547 BC547 BC547 whose collector TP0 is connected to GND the base of transistor T6. When DIS1 LTS542 16 Vcc 12 6 b b O2 of IC5 goes 7 a 7 A0 13 a 9 f high, it locks the 1 A1 15 10 g IC4 f 1 e door and makes 2 A2 74LS47 g 14 2 d 6 A3 9 4 c the Vcc pin 8 of e 5 dp 3 LT 10 d COM IC1 low to stop 4 BI/RB0 11 3 c further counting. 5 RB1 8 GND To open R11 470E the lock, press switches S3 and N/O S4 (acting as seCON2 L CON3 LIGHT D1 MAINS curity keys) siN N/C 14 1N4007 multaneously. RL1 6 TP4 N/O The mononsta1 CON4 D2 R9 T3 N/C ble circuit built LOCK 1N4007 1K BC547 RL2 + CON5 around NE555 _ 13 LOCK T4 (IC6) triggers and 8 SUPPLY R10 1K BC547 7 its output goes TP5 high for around RL1,RL2 = 5V 1C/O RELAY 11 seconds and

Fig. 1: circuit diagram of the automatic lock and lights circuit www.efymag.com

Electronics For You | February 2014

127

dIy: circuit Parts List

Fig. 2: An actual-size, single-side PCB for the automatic room-lock and lights circuit

Semiconductors: IC1, IC2, IC6 - NE555 timer IC3 - 74LS192 synchronous up/ down decade counter IC4 - 74LS47, 7-segment decoder/driver IC5 - HEF4002B dual 4-input NOR gate T1-T7 - BC547 npn transistor DIS1 - LTS542 common anode 7-segment display D1-D2 - 1N4007 rectifier diode Resistors (all 1/4-watt, ±5% carbon): R1, R5, R12 - 47-kilo-ohm R2, R3, R6, R7, R13 - 10-kilo-ohm R4, R8-R10, R14-R16 - 1-kilo-ohm R11 - 470-ohm Capacitors: C1, C3 - 100µF, 16V electrolytic C2, C4, C6 - 0.01µF ceramic disk C5 - 220µF, 16V electrolytic C7 - 470µF, 16V electrolytic Miscellaneous: CON1-CON5 - 2-pin connector S1, S2 - Foot switch S3, S4 - push-to-on switch RL1, RL2 - 5V, 1 C/O relay - 5V DC adaptor - Door-lock assembly

persons present in the room. the outputs O1 and O2 of IC5 remain low, so light remains on and door remains open till the room is vacant.

Construction and testing

Fig. 3: Component layout for the PCB

makes the base of transistor T4 low, via transistor T5. This action de-enegises relay RL2 to open the lock for a pre-defined time period based on the values of R12 and C5. At least one person should enter the room within this time period, otherwise it will get locked again. During this period, Vcc pin 8 remains high to enable IC1. When each person enters the room and presses foot switch S1, counter IC3 128

February 2014 | Electronics For You

advances by one count and display shows the number of persons in the room. On first person’s entry, the outputs O1 and O2 of IC5 go low, transistors T3 and T4 stop conducting and relays RL1 and RL2 de-energise to switch on the light and open the door lock. Similarly, when they start leaving the room by enabling foot switch S2, counter IC3 reduces by one count and the display shows the number of

An actual-size, single-side PCB for the circuit is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on PCB, enclose it in a suitable case. Switches S1 and S2 should be installed as explained earlier. The display can be installed on the door frame outside the room. Fix switches S3 and S4 at a suitable location such that you can press them simultaneously when needed. Connect the door-lock assembly to relay RL2 contacts using external wires as shown in Fig. 1. Use a 2-pin connector each for connecting the light and lock assembly. EFY note. Avoid entry of more than nine persons. Otherwise, at the entry of 10th person, the display will show ‘0,’ the door will get locked and the lights will switch off. If this happens, someone will have to press switch S2 from inside the room to open the lock and switch on the lights.  The author is a lab engineer at EFY Lab www.efymag.com