This LDR based alarm can be used as get up alarm.
The Alarm turns on in the morning automatically and turns off only when
manually switched off ,so you will have to get up. It is a simple LDR
based light sensor circuit.
LDR or Light Dependent Resistor is a kind of variable resistor
and its resistance depends on the intensity of light falling on it. In
complete dark, its resistance is as high as 1 Meg Ohm, but it reduces to
100 ohms or less in full light. So it is an ideal device to use as
light switch. Sensitivity of LDR depends on its size also. Commonly
available sizes are 3mm, 5mm, 10mm etc. But costly types with greater
sensitivity are also available.
When the circuit is place in dark, near
the window, LDR fails to conduct and T1 will not get base bias. So it
remains off and buzzer will be silent. When the sunlight falls on LDR,
IN the morning, LDR conducts and provides base bias to T1. T1 then
conducts to activate the buzzer. Capacitor C1 is provided for the clean
switching of T1. T1 will conduct only when C1 is charged fully. This
prevents chirping sound during light transition.You can use an easily
available Music buzzer to get melody tone.
