This alarm circuit was found in the July 1992 Radio Electronics magazine. The circuit uses a small power stage for the speaker and has the sensitivity adjustment at R5.
Found in an Electronics World of 1968 this circuit can use any SCR and diodes depending on the...
This 1 kHz triggered oscillator was found in an Electronics Now from the 90s. The circuit fires off...
We found this amplifier in an English publication from 1993. The circuit can be assembled today...