Found in a 90s Electronic Design, this circuit is used with a 9 V adapter for powering small circuits. The maximum current is given by the 250-mW regulator.
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...