This approach alarm circuit was found in the September 1970 Radio Electronics issue. The 1 mH coil is wound on a ferrite rod. The relay is 12 V sensitive.
This oscillator was found in the September 1984 issue of Radio Electronics magazine. The frequency is...
This simple 555 biofeedback circuit was found in the December 1983 issue of Radio Electronics...
Found in documentation from the 1980s, this circuit generates signals that can reach a few...