Security Alarm with LDR | LDR Latch Circuit
in this circuit simple LDR latch when any object enters between LDR and led object block light falling on LDR front Ldr resistance change because of light intensity and circuit off
Components list
1. LDR (Light Dependent Resistor)
2. C1815 Transistor
3. 220-ohm resistor
4. 330-ohm resistor
5. 3volt LED
6. Relay 6 volt
7. AC 220 volt bulb
8. AC plug
9.Switch click
10. 6 volts 1.5 amp supply
The aim of this video is to make a laser light security alarm. So that, it can also be used as a home security system. The Soul of this circuit is that we can design it for our houses to save them from thefts.
The laser security alarm circuit produces a highly audible buzzer beep sound whenever the laser light is blocked.
The purpose of LDR in this circuit is to sense the laser light from the laser diode.
WORKING:
Two NPN(BC548) transistors are used as switching devices in this alarm circuit. LDR is connected to the base terminal of Q1 transistor with resistor R1(100Ω) so that this LDR observes lower resistance whenever the laser light from laser the laser diode falls on this LDR and observes higher resistance when there is no light because of the 5V voltage source to Q1 transistor depends on the LDR resistance.
The Collector terminal of the Q2 transistor is connected to the buzzer and the LED and resistor R3 is connected to the same terminal. However, the Base terminal of Q2 is connected to the collector terminal of the transistor Q1. The 5V voltage source is used because every transistor needs some threshold voltage to get itself turned “ON”. When laser light falls on LDR, then it allows the supply to move to the base terminal of Q1 causing it to turn “ON”. As a result of this, the base of transistor Q2 doesn’t observe any bias, keeping the Q2 transistor in an OFF state. The LED and buzzer will also be in the OFF state.
When we block the laser light with the help of any piece of cardboard, the LDR is turned to high resistance and there is no voltage flow to the base of the Q1 transistor. The Q1 transistor is then turned OFF but the Q2 transistor gets supply and gets turned ON (causing the LED and buzzer to turn ON by giving a beep sound).
PRECAUTIONS:
There are a few things that must be taken into the study while designing the hardware:
1) This circuit produces a beep sound until the laser light is continuously blocked or interfered with.
2) Use glasses while operating this circuit because laser lights are dangerous to our eyes and need proper care.
3) The positioning of the LDR and light is very important.
Security Alarm with LDR | LDR Latch Circuit
in this circuit simple LDR latch when any object enters between LDR and led object block light falling on LDR front Ldr resistance change because of light intensity and circuit off
Components list
1. LDR (Light Dependent Resistor)
2. C1815 Transistor
3. 220-ohm resistor
4. 330-ohm resistor
5. 3volt LED
6. Relay 6 volt
7. AC 220 volt bulb
8. AC plug
9.Switch click
10. 6 volts 1.5 amp supply
The aim of this video is to make a laser light security alarm. So that, it can also be used as a home security system. The Soul of this circuit is that we can design it for our houses to save them from thefts.
The laser security alarm circuit produces a highly audible buzzer beep sound whenever the laser light is blocked.
The purpose of LDR in this circuit is to sense the laser light from the laser diode.
WORKING:
Two NPN(BC548) transistors are used as switching devices in this alarm circuit. LDR is connected to the base terminal of Q1 transistor with resistor R1(100Ω) so that this LDR observes lower resistance whenever the laser light from laser the laser diode falls on this LDR and observes higher resistance when there is no light because of the 5V voltage source to Q1 transistor depends on the LDR resistance.
The Collector terminal of the Q2 transistor is connected to the buzzer and the LED and resistor R3 is connected to the same terminal. However, the Base terminal of Q2 is connected to the collector terminal of the transistor Q1. The 5V voltage source is used because every transistor needs some threshold voltage to get itself turned “ON”. When laser light falls on LDR, then it allows the supply to move to the base terminal of Q1 causing it to turn “ON”. As a result of this, the base of transistor Q2 doesn’t observe any bias, keeping the Q2 transistor in an OFF state. The LED and buzzer will also be in the OFF state.
When we block the laser light with the help of any piece of cardboard, the LDR is turned to high resistance and there is no voltage flow to the base of the Q1 transistor. The Q1 transistor is then turned OFF but the Q2 transistor gets supply and gets turned ON (causing the LED and buzzer to turn ON by giving a beep sound).
PRECAUTIONS:
There are a few things that must be taken into the study while designing the hardware:
1) This circuit produces a beep sound until the laser light is continuously blocked or interfered with.
2) Use glasses while operating this circuit because laser lights are dangerous to our eyes and need proper care.
3) The positioning of the LDR and light is very important.
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