### Resistor color code

A resistor is the most important electrical component in almost every electronic circuit, it can limit current to any load such as led, transistor, opamp, etc. We must read resistor color code if we want to know the resistive value, tolerance, temperature coefficient. Resistors have different color bands (3,4,5,6) the more color bands the more resistor's information.Now let's start with 3 bands resistor color code.

The above resistor has only 3 bands First digit, Second digit, and multiply. A 3 bands resistor color code has fixed +/-20% tolerance that means if color code value is 1,000 ohms the real life resistive value may be +/- 200 ohms.
4 band resistor color code

A 4 bands resistor color code has tolerance value color strip, the resistor on an above picture has 5% tolerance. This type of resistor uses in a regular circuit such as television,radio,washing machine.

5 bands resistor color code

A 5 bands resistor color codes have third digit color bands.
1(first digit) 0(second dig…

## 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 model if you want smaller circuit.

Component list
5 volts Buzzer
1 kilo-ohms resistor
3 leg limit switch
SCR 3p6mh (You can use another SCR model without any problem just check K, A, G pin is correctly used)

Door security alarm circuit diagram

Door security alarm working and circuit explain

Feel free to ask any question about my project in comment box below