We found this circuit in a 1963 Radio Electronics. It can be used for remote control. The frequency depends on the coil and the power is supplied by a single battery.
This simple lie detector was found in Popular Electronics. Transistors are commonly used. The...
This one-transistor alarm can be used with much more sensors than the two shown by the figure....
This circuit was obtained in a 1975 documentation. The maximum frequency depends on the diodes and the...