Using a 4046 PLL this circuit generates rectangular signals in three wavebands that depend on the capacitors used. The circuit is from a Radio Electronics from December 1989.
This circuit from Popular Electronics powers a small speaker. The transistor can be of general use...
When the sensor X1 is opened, the relay is energized. When waiting, the current drained is very...
This circuit for measuring bridges was found in the October 1995 issue of Electronics Now...