ECL exclusive-NOR gate (F100107) and a length of cable form a simple ring oscillator, the delay from the cable and the gate determine the ring oscillators frequency, 100m cable yields approximately a 1 MHz oscillation frequency
Silicon controlled rectifiers (SCR) can easily oscillate if there is an inductor (a speaker coil in this case) which gives just enough extra voltage to completely switch off the sustain current. In this way a new cycle may start and oscillations set in. I
two gates from a CMOS 4011 NAND chip form a simpel square wave oscillator where the mark space ratio can also be independantly controlled by varying the value of the resistors
continuously operating 32KHz crystal oscillator to the input of a C-MOS buffer when clock pulses are needed, standby power consumption to a very low 1uA when used with a 3v supply.
Tutorial with Hartley VCO circuit.