Intruder detector Burglar alarm that auto-activates at Night

Hello Engineers. I hope you ‘re doing good. In the place like godowns, construction sites, telecom sites, small factories, Lawns, etc, high security is required and also present. But at some of those places, working hours are only during day time. So, during the night when security guards aren’t much active, we need to automate the security. A system is needed to alert the nearby security and staff which is called the Intruder detector Burglar alarm system. An intruder detector or burglar alarm circuit is needed to automatically detect the intruders & alerting the authorized security guards or officials. By making very loud sirens or sounds. These systems are put at the entry and are activated during the no-entry time to detect intruders activity. So let’s move further and let’s start with our topic ” Intruder detector burglar alarm circuit”. Or automatic intruder detector burglar alarm which auto activates when it’s dark.

This circuit is made on one of my website’s visitor’s request.

 Chima Hillary
 April 25, 2020 at 7:39 pm I want a circuit, an intruder alarm circuit that only activate at night time when any intruder enters my Telecom site at night. 

Aabhishek
April 25, 2020 at 7:44 pm
Hello Chima, Thanks for visiting my web site, and I will design and upload the circuit within the next 2-3 days and will let you know. Thank you.

So, basically Chima Hillary is one of my readers. He wants an intruder detector alarm circuit which is powered on all day but is only auto-activated when it’s dark. And generates a loud alarm only when it detects someone to enter their telecom site’s gate at night.

What is an Intruder Detector Burglar Alarm?

An intrusion detection alarm or burglar alarm is an alarm circuit which is consisting of some electronics components & sensors. Used to detect any human activity or entry gate security violations. The alarm makes use of different types of sensory elements like motion sensor or laser security alarm, for intrusion detection. After sensing, the sensor gets activated and thus sends a signal to the circuit which then activates the alarm system.

Also, kinds of circuits can be turned-on either manually by any authorized-person or made to get auto-activated after working hours. Below is the circuit for this project followed by the components list and explanation.

Circuit Diagram for Automatic Intruder detector Burglar alarm

Components needed

• PIR sensor 1pc
• LDR – 2pc
• R1 820K -1pc ( you can also use 750K according to your sensitivity adjustments, to be tested practically with the both)
• Q1,Q2 TIP122 -1pc
• D1,D2,D3,D4 – 1N4007 – 4pcs
• RELAY 12V – 2pcs
• DC Barrel jack female connector ( buy from amazon|this-one-is-non-profit-link)
• 12V 2 – 4.5AH SLA Battery ( available online cheap on amazon @ $11 only )
• 12V 2 A broadband DC adapter
• C1 330n – 1pc
• C2 100n – 1pc
• 220 V ac electric GONG BELL 9 inch (check the price online if it’s not in local shops)
• PCB
• Heat sink for Q1 and LM7805

Basic Principle

The circuit, as well as the materials list, are given above. The whole circuit is mainly powered by a 12v DC adapter during day time and 12v battery during the dark. This circuit has been made with custom features for one of the readers. This circuit has additional independency feature as it’s not needed to power-ON or Off. The circuit is a loud sound alarm burglar alarm with enhanced functionality that it automatically turns ON on detecting dark. After that starts serving its motion detection and human detection work. On detecting day time, it auto-shuts down and then the battery starts charging via DC adaptor.

WORKING OF THE CIRCUITRY

Here, 2 LDRs (Light Dependent Resistor) are used to detect dark, and PIR(Passive infrared sensor) is used to detect motion. As we know, LDRs have some working conditions and principles. With the increasing intensity of the light beam falling over them, LDR’s resistance is decreased and vice-versa. When resistance is decreased, of course, the conductivity is increased.

The 12v DC adaptor is always ON and powering LDR, Relay 1 as well as charging the battery. During the daylight, both of the LDR’s resistance is dropped very low i.e. As low as from 1M ohm to 100ohms. So now, R1 is greater, and this makes the Q1’s base to get shorted with the ground (low resistance barrier). Now, RELAY is also off due to Q1 TIP122 is off and relay keeps COM connected to NC. On the other hand, it also keeps charging the 12v battery in cycle mode.

With the decrease in Daylight, till evening when it starts to be dark, the LDR’s resistance reaches its peak.

Now, there is enough barrier between the base and the ground to turn the transistor ON. The transistor Q1 when turned ON, also turns the relay ON. Now, the relay’s COM is connected to NO by relay’s moving rod. This then makes battery power to supply the LM7805 regulator. The output of LM7805 powers the VCC of PIR.

PIR sensor is then turned ON after getting +5V Vcc in. Everything is silent until the PIR detects any motion activity. Once the PIR detects the motion activity, it gives a TTL output to transistor Q2. Q2, on getting turned ON, makes the relay activated. An electric GONG bell is also connected to the relay’s NO. Now the relay makes the circuit between 220v supply and the electric gong bell complete. A loud sound up to several meters.

INSTALLATION AND BASIC USAGE GUIDANCE

• Use a 12v 2A DC adaptor connected to the DC barrel jack. Always keep it ON.
• Keep circuitry away and safe from water.
• Arrange the PIR sensor’s position so that it is only detecting that who has entered inside from gate. Or site ( telecom site for example) entrance.
• Position the LDR’s in such a way that they get clear view of light and dark. I suggest put circuitry in a waterproof arrangement and make LDRs to face sky.
• Just always keep 12v 2a DC adaptor ON and it’s ready.

So guys, this was all about this circuit. I hope you liked it, if you have any questions regarding this, you can ask me in the comment section. Thank you.