The transistors of this circuit found in a 1965 magazine can be the BC558 and the sensitive 12 V x 50 mA relay. The other components are common.
Here we show an oscillator that uses an LC network. The upper limit depends on the power-supply...
This circuit from a Popular Electronics from the 90s allows you to use an old PC as a digital...
of the National Semiconductor of 1994. The same technique can be used with other operators and the...