The integrated circuit used is uncommon today. The circuit was obtained in the Philips integrated circuits manual of 1990. The reference voltage-range is from 0.5 to 9.0 V.
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...