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Home security using IR







In this project we will use laser for security. A laser


Beam will fall on LDR or Photiode. On other hand detector will give signal to signal conditioning circuit. We are using 89s52 micorntroller as a brain. 89s52  is 8051 series IC. 89s51 have 8k byte ROM , 256 byte RAM.  We will give output of sensor circuit to microcontroller ciruit. Microcontroller will give signal to buzzer and relay drive circuit. Relay drive circuit will switch on / off lights.

It is very necessary to protect home using these technologies.


We used laser because it covers large area. Defaul laser will fall on detector. If laser beam will not fall on security system



In this sensor unit  it is our choice , how many sensorís  we use , IN this project we use two sensorís, In this project we use two electronics circuit with infra red sensorís and fire alarm sensor.


In the infra red sensor. We use ic 555 as a main component. Pin no 4 and pin no 8 is connected to the positive supply. Pin no 1 is connected to the negative voltage. One capacitor is grounded from the pin no 5 for noise cancellation. Output is available on the pin no 3. Sensor is connected to the pin no 2.


In the case of infra red sensor. Pin no 2 is negative bias through the 33k ohm resistor and pin no is positively biased through the photodiode. One infra red transmitter l.e.d is  focused to the photodiode . Infra red l.e.d is directly connected to the positive and negative supply through the 470 ohm resistor..


In normal stage when light is focus on the photodiode then  pin no 2 is positively biased photodiode. If pin no 2 is positive then  negative  output is available on the pin no 3. Now when any body interrupt the light then  there is no light on the photodiode and pin no 2 is now gets its voltage from only 33 k ohm resistor.  If pin no 2 is become negative then  output is shifted to the  pin no 3. when positive output is available on the pin no 3 and with the help of this voltage  NPN transistor is on and npn transistor provide a negative voltage as a pulse to the microcontroller.


If we connect two sensor as a input to the microcontroller then we use same circuit with the ic 555 .

 Note that microcontroller sense only negative input to the microcontroller.




ATMEL AT89C2051 Pinout and Description

The 2051 is a low voltage (2.7V - 6V), high performance CMOS 8-bit microcontroller with 2 Kbytes of Flash programmable and erasable read only memory (PEROM). This device is compatible with the industry standard 8051 instruction set and pinout. The 2051 is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications. The 2051 provides the following features:

~ 2 Kbytes of Flash
~ 128 bytes of RAM
~ 15 I/O lines
~ two16-bit timer/counters
~ five vector, two-level interrupt architecture
~ full duplex serial port
~ precision analog comparator
~ on chip oscillator and clock circuitry

In addition, the 2051 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port and interrupt system to continue functioning. The Power Down Mode saves the RAM contents but freezes the oscillator disabling all other chip functions until the next hardware reset.

To learn how to use the 2051 microcontroller, get the Microcontroller Beginner Kit (click here)

2051 - 24MHz DIP Available

The 2051 can be programmed using a device programmer such as the PG302 (Click Here).

We also have Projects that use the 2051 Microcontroller.
See the Intermediate Tutorial Section.

This page last updated on April 7, 2003.




All the input sensor is connected to the pin no 18 and 19. Pin no 18 is connected to the P1.6, and pin no 19 is connected to the P1.7. pin no 20 is connected to the positive supply. Pin no 1  reset pin. One capacitor is connected from positive to pin no 1 and one resistor is  grounded from pin no 1. One microswitch is connected  across the  capacitor fro manual reset switch.


One buzzer is connected to the pin no 16 ( Port p1.4) this buzzer is on when  circuit sense a input from the  input sensorís. .



Components required:


Ic 91214

89s52 microcontroller

push to on sw

555 timer

 .001 Ķf,0.1 Ķf,0.01Ķf



crystal 11.0592 MHz

3.38 MHz.


condenser Mic

speaker 8 ohm

relay 12v 100 ohm

transformaer 6v 500mA

infrared Sensor,

heat Sensors

connecting wires

copper clad board








Easy to implement


Low cost,

Components easily available in market.