Simple Alarm

Here is the Simple Alarm circuit using SCR.

Components Required:

1) Breadboard

2) 1N4007 Diode

3) 470 ohm resistor

4) 100 kilo ohm resistor

5) LED (Any Color)

6) C106 SCR

7) Buzzer

8) DIP Switch = 2

9) 9Volt Battery

Procedure:

• Connect the circuit as shown in the circuit diagram below.
• Close the S1 switch and switch S2 is kept open therefore there is no gate current and the SCR remains OFF.
• Hence the LED and alarm connected to the circuit also remains OFF.
• Now close switch S2 also therefore gate current is applied which triggers the SCR to ON state and the gate terminal looses its control and cannot be used to switch OFF the SCR.
• Hence the LED and alarm connected to the circuit switches to ON state.
• To switch OFF the SCR, decrease the gate current below the holding current of the SCR or disconnect the gate current.

 Circuit Diagram:

Figure 1: Simple Alarm Circuit simulation made in Multisim (S1 Closed & S2 Open)

 

Figure 2: Simple Alarm Circuit simulation made in Multisim (S1 & S2 Closed)

Figure 3: Simple Alarm Circuit (S1 & S2 Closed)