This circuit automatically turns off small battery-powered devices after a certain amount of time, saving battery life. We found it in a Popular Electronics from the 90s.
This circuit makes use of an operational amplifier from the 80's. The circuit can be implemented with...
When the power is cut off, this circuit keeps the flashlight on for a while, allowing it to be...
Using the CK722 this directional photometer was published in Radio Electronics magazine in July...