This circuit was found in Linear Technology Applications of 1997, using components of the time. The circuit transmits video signals bidirectionally over twisted pair.
This 1967 Raytheon circuit uses an optical coupler of the era and has a range of 800 to 200 Hz....
This interesting digital counter with relays with complementary outputs was found in the Radio...
This circuit uses a diode as a radiation sensor. The operational ones are old because the...