Light-sensitive Alarm Project


Posted on Feb 4, 2014

The circuit detects a sudden shadow falling on the light-sensor and sounds the bleeper when this happens. The circuit will not respond to gradual changes in brightness to avoid false alarms. The bleeper sounds for only a short time to prevent the battery running flat. Normal lighting can be used, but the circuit will work best if a beam of light i


Light-sensitive Alarm Project
Click here to download the full size of the above Circuit.

s arranged to fall on the light-sensor. Breaking this beam will then cause the bleeper to sound. The light sensor is an LDR (light-dependant resistor), this has a low resistance in bright light and a high resistance in dim light. Using the 7555 low-power timer ensures that the circuit draws very little current (about 0. 5mA) except for the short times when the bleeper is sounding (this uses about 7mA). If the circuit is switched on continuously an alkaline PP3 9V battery should last about a month, but for longer life (about 6 months) you can use a pack of 6 AA alkaline batteries.




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

LM555 LED Blinkers
Dc-latching-relay
The Arduino Internet Gizmo
A Bedside Lamp Timer Circuit Schematic
usb powered mobile phone battery
Stepper Motor Generator
Audio
Miniature FM transmitter circuit
Arduino Analog Read Potentiometer to Digital Out LED
RIAA Corrector
FET Preamplifier
A Cmos Based Motorcycle Alarm circuit
1999 mercury sable: wiring diagram illumination a 3.0L vin U. I
Motorola Mitrek conversion to repeater or link



Top