Power Grid Monitor (CB21154E)

We found this circuit in a Popular Electronics from the 90s. Its purpose is to monitor a power line. The circuit uses optical couplers of the time.

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Headphone Extensions (CB23790E)
The figure shows three circuits for using headphones in amplifiers with speakers that do not have...
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In this charger, the charging current is basically limited by the LEDs. The transformer is a low...
Fast Voltage Follower (CB4904E)
This configuration is from an old integrated circuit manual. The circuit can be applied to modern...