In this 2001 circuit we have the way to trigger an SCR with a phototransistor. The circuit appears elsewhere in this section, obtained from publications from different eras.
This circuit was obtained from the CA3140 datasheet. This component consists of an operational amplifier...
In the figure we have one of the many options found in this section for an intercom using ordinary...
Found in Electronics Now from the 90s, this circuit can use any general-purpose transistor. The power...