This setting applies to virtually any photo transistor and any operational amplifier. The power supply must be symmetrical, and the gain is determined by the relationship between R2 and R1.
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...