In the figure we have a basic shield circuit with TTL to TTL optical isolator. For the emitting LED the voltage can be different from 5 V.
This circuit was found in a 1970s RCA publication. Transistors support modern equivalent types....
We found this circuit in Motorola's Linear Databook in 1990. The component used is not common today....
This basic op amp filter configuration was found in July 1975 Radio Electronics magazine. The...