This circuit, with printed circuit board included, is from a Radio Electronics magazine from July 1971. The SCR can be any equivalent of the 106 series.
This simple blocking oscillator using a transistor can be used in alarms or call systems. The...
The circuit in figure 10 uses two of the 4001's four ports to trigger a relay in a timed manner. The...
Other series comparators such as the LM239 and LM339 can be used in this oscillator circuit. The...