This circuit from a Popular Electronics from the 90s uses a common optocoupler and a general-purpose transistor to control a sensitive relay that can be from 6 to 12 V.
This circuit that can amplify signals from 0 to 30 MHz was found in a 90s Popular Electronics....
August 2017 - STMicroelectronics' BlueCoin development environment is available at Mouser...
In this circuit the output current is limited by R3. For a 300 mA current, R3 must have 12 Ω. For...