Easy and work project

Hello, today I will show you how to make a security door alarm, the door alarm is easy to make and give the best result. The door security alarm provides a very long battery life and easy installation, the circuit use only 2.4 volts to operate so you can power the circuit with 2xAA rechargeable battery or even you can use a lithium-ion battery with auto charging circuit as power supply because the circuit can withstand up to 5 volts power supply.  If you want to change the power supply to 12 volts, you simply need 7805 IC to regulate 12 volts to 5 volts without any problem. You also can use 12 volts Buzzer instead 5 volts Buzzer that I used in the circuit and connect directly to 12 volts power supply (solar charger's output, 12 volts car battery). The SCR (thyristor) in this circuit can withstand current up to 3 A so you can connect 20 Buzzers (estimate 100 milliamp/hour per Buzzer) with one circuit module without making any damage to The SCR. You also can change the SCR

If you want to make a simple VU meter. LM3914 is the best choice for you. It's easy to make VU meter or 10 dot/bar DC level meter with lm3914.  lm 3914 can withstand +-35 volts input without any damage so you can make VU meter even you are new in electronic DIY. The circuit uses minimal component to make the job done. List of component: R1 = 1 kilo-ohms R2,R3 = 4.7 kilo-ohms R4 = 10 kilo-ohms ic = lm 3914n-1 (lm3914) C1 = 4.7 uf at least to 47 uf (better bass respond) 10 LEDs red,green,yellow,orange or whatever you want 9 - 12 volts DC power supply LM3914 schematic diagram    Lm3914 VU meter video, the video show step by step guide and circuit explanation. Now, I add a sine wave rectifier circuit to lm3914, it makes the dot mode more accuracy. Real dot mode VU meter schematic diagram