Schematics > Security and other sensors and detectors > DayLight Alarm
DayLight Alarm
The circuit presented here wakes you up with a loud alarm at the break of the
daylight. Once again the 555 timer is used here. It is working as an astable
multivibrator at a frequency of about 1kHz.
The circuit's operation can be explained as follows:
When no light falls on the LDR, the transistor is pulled high by the variable
resistor. Hence the transistor is OFF and the reset pin of the 555 is pulled low.
Due the this the 555 is reset.
When light falls on the LDR, its resistance decreases and pulls the base of the
transistor low hence turning it ON. This pulls the reset pin 4 of the 555 high
and hence enables the 555 oscillator and a sound is produced by the speaker.
The variable 100K resistor has to be adjusted to set the light intensity that
triggers the alarm.
Title: DayLight Alarm
Source: www.electronic-circuits-diagrams.com
Published on: 2005-02-01
Reads: 459
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