Electronic circuits > Alarms/Indicators > DayLight Alarm
DayLight AlarmThe 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.
Published on: 2004-08-21 (4183 reads)
[ Back | Home ] |