Circuit Design of Intruder Alarm Circuit on 555 IC Based

In this tutorial, we are going to learn about Circuit Design of Intruder Alarm Circuit on 555 IC Based.

Below are the working of circuit Intruder Alarm Circuit on 555 IC based.

Below is the circuit diagram for an ultra-sensitive intruder alarm. If the shadow of an intruder passing few meters nearby the circuit the it is enough to trigger the alarm. Here IC2A (741) is connected as a sensitive comparator, which set point is set by R6 & R7 and in this circuit always use for voltage divides by LDR and R9 is given at non inverting pin of IC2. When this circuit on the standby mode these two voltages are set equal by adjusting R9 in case the output (pin6) of LM741 will be high and that time transistor Q1 will be off. When the voltage at trigger pin of IC1 will be positive and in case there will be no alarm. If put an intruder near the LDR the shadow causes its resistance to increase. Now the voltages at the input of IC2 will be low. This makes Q1 on. This makes a negative going pulse to trigger the IC1 which is wired as a Mono- stable multivibrator. The output of IC1 will be amplified by Q2 (SL100) to produce alarm.

Below is the list of Part for Intruder Alarm Circuit Diagram.

Sr No.Part ReferenceValueQuantity
1R1,2,3,51K4
2R41M1
3R6,710K2
4R8LDR1
5POT470K1
6D1LED1
7Q1BC1571
8Q2SL1001
9IC27411
10IC1NE5551
11K1BUZZER1
12C10.01UF1
13C210UF1

Intruder Alarm Circuit Diagram Features

  • If the set-up the alarm, power up the circuit and adjust R9 so that LED D1 goes off.
  • The LDR can be close in a dark tube to increase sensitivity.
  • In this circuit sensitivity is must when anyone cannot adjust the required sensitivity properly, generally use one LOW resistance (1k) POT in series with R9 for fine adjustment.

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