This simple tester was found in a Popular Electronics from the 90s. The circuit is powered by two 9 V batteries since it requires a symmetrical source.
This circuit triggers an oscillator when any of the sensors is opened. The circuit can be powered by...
This circuit imitates the singing of a bird intermittently with the intermittency determined by C1...
This is a high gain circuit with 3 transistors connected in direct coupling. The circuit is from a...