This type of answering machine was common at the time this circuit was published. Using two tape recorders, it was published in the June 1986 issue of Radio Electronics magazine.
In the figure we have a circuit to excite a piezoelectric capsule taking advantage of its resonant...
This sensitive two-transistor current meter was found in the June 1964 Radio Electronics magazine....
This circuit was found in Radio Electronics from the 90s. The circuit can generate signals up to...