Shadow Alarm with the 741 IC (ART429E)

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

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

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

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

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.