This alarm can be used for various purposes, such as for indicating the burning of lamps in an ambient light system, the presence of persons in a passage, as suggested in figure 1, and the very darkening of the environment at dusk.

 

Figure 1 - The alarm
Figure 1 - The alarm

 

In Figure 2 we then have the complete circuit of our alarm which is powered by a symmetrical 9 V source.

 

Figure 2 - Alarm circuit
Figure 2 - Alarm circuit

 

This source can be formed by two 9 V batteries connected as shown in figure 3.

 

Figure 3 - 9 V symmetrical power source
Figure 3 - 9 V symmetrical power source

 

Or if the reader wants, it may be the source shown in figure 4.

 

Figure 4 - another dual symmetric source
Figure 4 - another dual symmetric source

 

The transformer used in the case has a primary according to the local network and a secondary one that provides a voltage of 9 V under a current of at least 250 mA.

Cl-741 or any of its equivalents

R1 - 470k - trimpot

R2, R3 - 199 k x1 / 8 W - resistors (brown, black, yellow)

R4 - 100 ohms x 1/4 W - resistor (brown, black, brown)

C1-O, 1, uF-polyester capacitor

C2 - 100 uF x 16 V - electrolytic capacitor

LDR - Common LDR of any type

FTE - 8-ohm speaker

Miscellaneous: Printed circuit board, fountain, wires, solder, etc.

 

Datasheets


N° of component