The circuit is from a June 1995 Electronics Now. The relay is power-dependent and both R1 and R2 should have close resistances in operation.
This filter was obtained from a Linear Technology manual from the 1990s. The power supply must be...
Found in a 90s Popular Electronics, this circuit is intended for amplifying analog video signals....
Based on a 555, this 80's American documentation circuit detects the voltage of a battery and can then...