This circuit maintains on a flashing LED at a frequency determined by the capacitor. The unijunction transistor can be 2N2646.
Found in Electronics Today International in the 90s, this circuit turns an operational on and off...
At dusk this circuit triggers a relay switching lamps. The circuit can be powered from 6 to 12 V...
This second-order low-pass Salen-Key filter was obtained from an American 1980s documentation. Formulas...