Light Alarm Circuit | Electronic Project Circuits

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Light detector by IC-timer 555

This is an idea for a light detection circuit,We use the 555 timer IC.Usually, we used to produce frequency (astable multivibrator) a lot easier.
The single IC with a a few resistors and capacitors, adjust value them to control the frequency output.Can drive speakers directly, as the buzzer sounds.The CDs LDR is a resistor to change its value with lighting.When applied at pin 4 (reset pin), if hight voltage this circuit is work. LDR and R3 together with characterized by a simple voltage comparison circuit.
When the light is very low resistance CDS, the voltage at Pin 4 is high, the circuit is to hear a voice come out.

Be the first to comment - What do you think? Posted by admin - September 17, 2011 at 8:54 am

Categories: Detector, Lighting Tags: cds controlled circuit, light alarm circuit, light detector circuit

Simple Darkness Activated Alarm by IC 555

Most darkness activated alarms employ opamps and some logic ICs. Here, a less expensive approach is shown based on the eternal 555, this time in monostable multivibrator mode. Components R2 and C1 represent a one-second network. When the LDR (light dependent resistor) is in the dark, its resistance is high, pulling pin 2 of the 555 to ground. This triggers the monostable and the (active!) 6-volt piezo buzzer will sound. Preset P1 is adjusted depending on ambient light levels. The circuit may be fitted on a wall in your home. Assuming P1 has been set for the existing ambient light level, the shadow cast by anybody entering the room or hallway will trigger the alarm.
Author: Myo Min – Copyright: Elektor July-August 2004
Source: http://www.extremecircuits.net/

Be the first to comment - What do you think? Posted by admin - August 11, 2010 at 7:22 am

Categories: Alarm systems, Lighting Tags: light alarm circuit, light dark detector circuit

Light Detector by IC CD4001

Variable resistor R1 adjusts the light threshold at which the circuit triggers. R1’s value is chosen to match the photocells resistance at darkness. The circuit uses a CMOS 4001 IC. Gate U1a acts as the trigger, U1b and c form a latch. S1 resets the circuit. The output device may be a low power piezo buzzer.