This circuit was found in the July 1986 issue of Radio Electronics magazine. The circuit has a loudspeaker warning system. The sensor is the ceramic capacitor C1 which acts as a transmission line.
This circuit was found in a 1977 Radio Handbook. The ports used are CMOS like 4001 and the...
I found this Vox circuit or acoustic receiver as it was originally called, in a 1973 publication. The...
Found in RCA documentation from the 90s, this bass and treble control uses an operational...