Found in Popular Electronics from the 90s, this circuit uses a reed switch on the rails as a sensor. Instead of lamps, in a modern version, LEDs can be used.
The cut-off frequency of the filter shown in the figure can be adjusted to values between...
This circuit was found in a Popular Electronics from the 90s. The components used are all common...
This circuit uses a dual floodgate MOSFET not very easy to obtain today. Its handling is very...