Hello friends,

This is a simple design alarm for your winter breaks. With this alarm you need not set time, it detects the day light in the morning and generates beep sound for approx. 1 minute. You need not set time for your winters, just set the sensitivity for the daylight detection through the potentiometer.

You can also modify this circuit for other uses.

Step 1: Explanation

This circuit has 4 modules.

1 : Light Detector Module

2 : Alarm Duration Module

3 : Beep Generator Module

4 : Sound Generator Module

1 : Light Detector Module

This module detects the light and as output gives high signal (9v) when the LDR is in dark place. and the output is low (0v) when the LDR is in light.

This circuit is very common and uses a very cheap IC LM358, it has 2 comparators in it, you can get the detailed explanation of this module easily on google.

2 : Alarm Duration Module

This module uses 555 timer IC in monostable mode, it uses the output of the light detection module as input, and generates high output for approx.1 minute after detecting the falling edge from the light detector module. I have used a capacitor of 10uF in between these 2 circuits which is a key element in triggering the 555 timer IC in monostable mode.

3 : Beep Generator Module

This module is a simple 555 timer circuit in astable mode, its output frequency is close to 1hz. This module is enabled by the output of the alarm duration module and starts producing the pulse when the alarm duration module gives high output.

4 : Sound generation Module

This also is a simple 555 timer circuit, but with high frequency, this module produces high frequency output pulse, which generates sounds when attached with a small 8ohm speaker. This module gets the enable signal from the output of the beep generator module.

Step 2: Circuit

to make this circuit you will need :

9v battery + clip x1
LDR x1
10k x5
20k pot x1
LM358 x1
LM555 x3
8 pin IC base x4
LED x3 [red,green,yellow]
1k x4
10uf x2
100uf x1
.1uf x1
1000uf x2
8 ohm speaker x1
dotted PCB 7x7cm x1

To build this circuit, you can use many methods, i made it using a dotted pcb (pref board). You should first do it on a breadboard, then implement it on PCB.

In this instructable i have not explained the method to build the PCB. I will try to make another instructable for that.

For time being, make the circuit in your own way.