|
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.
|
