Isolated shield using photo SCR (CB8077E)

This circuit is from a Popular Electronics from the 90s. It uses an opto-coupler with SCR directly controlling a 20 mA current load.

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5 MHz oscillator with 250 kHz variation (CB13852E)
We found this oscillator in a documentation for radio amateurs from the 1970s. The circuit can use...
Impedance Matcher (CB15540E)
Many oscilloscopes have high impedance inputs that make it difficult to observe high frequency signals...
Optical Communicator – Receiver (CB25536E)
This is the receiver for the previous circuit we found in the December 1992 Radio Electronics...