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Following circuit is an automatic DC light switch, it run the load in dark. the load can be a lamp or any other device, works by 3 to 12 volts It is possible to use this circuit as anti theft system if we connect a laser and an alarm, so when opens the door, laser ray move from LDR and alarm be turn on. T2 should be changed by any other power NPN transistor if the load consumed more than 100 mA. Parts list: Transistor BC547 (2pcs) LDR Resistor 100k Resistor 1k Note: if you want to use LED as load, so have to use protection resistor 200 ohm for 3v battery or 680 ohm for 12v battery.

LEDs because of the diversity of colors, strong lighting and consume little power used in many areas, can use for write letters and draw shapes. In following video you can see how it can. The LEDs must connect together in parallel, means all positive connect together and all negative connect together so you can run that with 2 to 3.5v (according to led types). you have to using a resistor through positive line to protect your LEDs and increase its life period.(see the note) you can use second method for big LED boards . Parts list: Breadboard (25cm x 12cm) battery Text or shape printed on a paper Solder flux LED(number of LEDs depend on your text or shape ) Resistor (see the note) Note:  Protection resistor used when supply power is more than standard LEDs voltage , its value depends on number of LEDs, LEDs type(color) and voltage of battery or power supply.  You have to using ohm's law for calculation the value of necessary resistor. in first run your LED board by 2 to 3v battery

The following circuit is simple circuit for sensing the presence of light Can change sensitivity of circuit by change the value of 8.2k resistor

The following circuit is Flasher which operates by 220 volts you can add many LED lights in various colors in parallel advantages of this flasher little cost and power consumption is very low To change the speed of the flash must change capacity of the capacitor Parts list: Diac DB3 or any other diac with breakdown voltage of 30 to 40v LED Capacitor 22uF-35v  Resistor 33K Resistor180ohm Diode 1N4007 Please subscribe to my YouTube channel here:  https://www.youtube.com/c/EngMousaalkaabi?sub_confirmation=1