Using 555 integrated circuits, this alarm circuit was found in a 90s American documentation. The signal must be applied to a good audio amplifier.
This is one of the many approaches we have on the site for this low power 0.5 W amp using the...
This circuit of a 1969 Electronic Design uses RTL logic. The setting can be adapted to TTL. The...
This circuit was obtained in a 1979 publication but can still be easily assembled today by...