Microprocessor based home security system

In this advance world security system is in high end so the security breakers are. Now it’s time to live free, live secure. By keeping these all thing in mind (problem from burglary) the innovative group dreamlover technology designed a microprocessor based project “Microprocessor-Based Home Security System”. This advance security system not only let you know but also alert police immediately. In the project 8085 microprocessor based home security system we can control siren, telephone (via cradle and redial switches) and cassette player (alert message is recorded already)

Working of the system

The whole circuit of 8085 based home security system consist transmitter, receiver, Phase-Locked-loop and processing section as shown in Block diagram.

 block diagram of microprocessor based security system

The mechanism of the project “Microprocessor Based-Home Security System” is very simple. As this project is IR based, the IR ray from transmitter is focused in the base of phototransistor of receiver fitted in opposite to each other. The property of phototransistor is that whenever the IR ray focused on its base is obstructed, the microprocessor as per program burnt in EPROM which further control siren, telephone and cassette player.

Circuit Description

The whole Project “8085-Microprocessor based security system” is divided into two main sections i.e. Hardware and Software.

 circuit diagram of microprocessor based security system

Hardware: The complete circuit-Diagram of “Microprocessor Based Home Security System” is shown in figure 1. The transmitter section is designed and fabricate around timer IC NE555 wired as astable multivibrator followed by transistor T1 and IR LED. The oscillated frequency of transmitter section is decided by resistor R1 and R2, preset VR1 with capacitor C1. The output from pin 3 of IC1 is given to base of transistor T1 through resistor R3 for amplification as per required and given to IR LED. The modulated IR signal is transmitted by IR LED1.

The IR transmitted signal is focused on the base of photo transistor. The output from photo transistor is given to transistor T3 followed by op-amp (IC2) for amplification. The amplified signal from IC3 is given to input pin 3 of Phase-Locked-Loop (PLL) IC LM567 (IC3) through capacitor C4. The normal use of PLL IC (IC3) is frequency decoder so is here in order to drive the load. The tuning frequency is determined by variable resistor VR2 and current controlled oscillator by resistor R12. The tuning frequency (6-10 KHz) should match with modulating frequency transmitted by transmitter. Pin 8 of IC3 is connected to base of transistor T4 through resistor R13. Glowing LED1 indicate receiving signal is locked to transmitting signal. Transistor T5 is used as relay driver in order to energize the relay RL5. Relay RL1 energized normally when transmitted IR signal falls on phototransistor T2, at this time microprocessor does not get any input. But when IR signal is interrupted microprocessor get high (TTL-level) signal through port A of Programmable Peripheral Interface (PPI).

The microprocessor start working as per command loaded in the EPROM (IC5) when high input is given from PLL. Octal latch (IC6) is used for interface between low-order multiplexed address and latch lines AD0 through AD7 of microprocessor (IC4) and EPROM in order to separate Address line A0 through A7 from data line D0 to D7 by latch-enable signal (ALE), while high-order address lines A8 through A10 is directly connected to EPROM.

ALE pin (30) of microprocessor is connected to pin 11 of IC6. The output changed according to input data when ALE is high, if ALE goes low the lower-order address is latch at the output of IC6.

RD and IO/M pin (32 and 34 respectively) of microprocessor (IC4) is used to generate Chip-Select signal (CS) with the help of NAND gates.

Pin 18, 19, 20 and 25 of IC7 are connected to base of relay driver transistor T6 to T9 through resistor R19 to R22 respectively. The high signal (interrupt of IR signal on the base of phototransistor) on these pin energizes the relay RL1 to RL4. For reset switch SW1 is used.

Polarity reversed in the telephone line is build around optocoupler ICs (IC8 and IC9). As we all know that normal TIP of telephone set is positive in compare to Ring LED of telephone line. When the handset is in OFF-HOOK position, a loop current of 10mA is assumed for flowing in telephone line.

When the polarity reversed occurs from DC line the internal LED of IC8 conduct which further glow LED3 for indicating polarity reversed. Internal LED of IC9 goes off and its pin 5 goes high in order to provide line reversed sense signal to microprocessor using pin 14 of programmable peripherals interface (PPI) IC (IC7).

Relay connection

The cradle switch of telephone set is replaced by DPDT relay (RL3). The four pads connection of PCB with cradle switch is now connected with relay. The two shorter distance pad when handset is placed in the cradle is connected to N/C contract of relay RL3 where other two pad which is shorter distance when handset is off-hook are connected to N/O contract of same relay. Relay RL2 is connected to redial bottom of telephone set parallel. When relay RL3 is energized relay RL2 is also energized to switch on the redial bottom which automatically dialed already loaded number (i.e. police or any help line). Relay RL4 activate siren when ever receiving IR signal is interrupted until the reset bottom is pressed. Lastly relay RL1 switched the audio cassette player in which victim detail is already recorded. The speaker connection of audio cassette player is connected to microphone of telephone to convey the alert message.

Software: The flowchart showed in figure: 6 shows the assembly language program. 99H word is used here to control device interface IC (IC7) where port A and C as input port and B as output. At first microprocessor read the status of port A, when port A is high siren is activated, redial switch is activated and emergency number is dialed. After dialing number redial bottom gets switch off. Now microprocessor read the status of port C which further checks the polarity reversal of telephone line.  After detection of polarity reversal, the audio player is activated. When the message is finished the player automatic gets turned off.

 flow chart of the programme

Click to download program code for microprocessor-based home security system

PCB DESIGN: The actual size of PCB board must be 17.5cm×9.7cm

 PCB design of home security system



Click to download PCB Design in high resolution




Resistors (all ¼-watt, ± 5% Carbon)

R1, R2 = 5.6 KΩ

R3, R16, R18 – R22, R25 = 4.7 KΩ

R4 = 100 Ω

R5 = 3.9 KΩ

R6, R8, R12, R15, R17 = 1 KΩ

R7, R10, R11, R13, R14 = 10 KΩ

R9 = 100 KΩ

R23 = 120 Ω

R24 = 470 Ω

VR1 = 47 KΩ

VR2 = 10 KΩ


C1 = 3.3 nF ceramic disc

C2, C6, C13, C14 = 0.1 µF ceramic disc

C3, C8 = 0.01 µF ceramic disc

C4 = 1 nF ceramic disc

C5 = 10 µF, 25V electrolyte

C7 = 2.2 µF, 25V electrolyte

C9 = 10 µF, 10V electrolyte

C10, C11 = 10 pF ceramic disc

C12 = 1000 µF, 50V electrolyte


IC1 = NE555 (timer IC)

IC2 = µA741 (operational amplifier)

IC3 = LM567 (Phase-Locked-loop)

IC4 = 8085 (Microprocessor)

IC5 = 2732A (EPROM 4k)

IC6 = 64LS373 (Octal Transparent Latch)

IC7 = 8255 (programmable peripheral interface)

IC8, IC9 = MCT2E optocoupler

IC10 = 74LS00 (NAND gate)

IC11 = 7809 (9V regulator)

IC12 = 7812 (12V regulator)

T1, T3 – T9 = BC548 (NPN transistor)

T2 = L14G1 (Phototransistor)

D1 = 1N4148 (Switching diode)

D2 – D10 = 1N4007 (rectifier diode)

LED1 – LED3 = Red LED

IR LED1 = Infrared Led


X1 = 230V/50 Hz or 110V/60 Hz AC primary to 12V-0-12V, 300 mA secondary transformer

XTAL = 3.5 MHz crystal

SW1 = Push-to-on switch

SW2 = On Off switch

RL1, RL2, RL4, RL5 = 12V, 200 Ω, 1C/O relay

RL3 = 12V, 200 Ω, 2C/O relay


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