BURGLAR ALARM

DESCRIPTION

*This is asimple but effective burglar alarm circuit that can be fixed on windows to detect break through.

*The circuit uses a fine wire element fixed as a network through the window  glass  for sensing the break through .

*Normally the base of Q1 is held to ground potential by the wire element.So Q1 will be off and SCR H1 will not be conducting,and horn will be off.

*When the  wire element is broken the base of Q1 will be raised to positive potential, Q1 will be on and so SCR H1 (TYN 612) will be ON making the horn to blow and this condition will be latched by the SCR

.

*The circuit remains ON until the normal condition is restored or the power supply is switched OFF.

NOTES

*To make the window foil make a loop of very fine wire through the window glass ( two or three lines running in both direction is enough).

*Connect the two  free ends of the wires to point A & B as shown in circuit diagram.

*To setup the circuit , make S1 open and adjust R2 to get a 1V between base of Q1 and ground.(0.7 V is enough to ON Q1).

*Now transistor will be ON and horn will be blowing.

*Now ,close S1 and reset the power supply .The transistor Q1 will be  off and horn will not be blowing. The circuit is ready.

CIRCUIT DIAGRAM

WINDOW FOIL STRUCTURE