This unusual circuit from a Popular Electronics of the 90s uses LED indicators, operating as a bridge. The components used are common. It is based on the tuning of the signal by a PLL.
Using an integrated circuit from the time, this circuit was found in Radio Electronics from the...
This shield circuit is from old documentation. The operational amplifier used is not common today...
This circuit powers a small 5 W lamp that goes out when power is lost. The circuit can use the...