This circuit was obtained in a Popular Electronics of the 90s. The circuit uses integrated from the time, uncommon today. Note that the speaker has a higher impedance than ordinary speakers.
This circuit is from Motorola's Linear Interface ICs of 1993. The circuit can be implemented with...
We find this circuit in an American 1980s documentation. It triggers an alarm in the event of a...
This circuit was obtained in a 70s American documentation. The integrated circuits of the time are...