This circuit was found in a Radio Electronics magazine from June 1962. The circuit is for cars of the time with platinum ignition. The indication is made on an analog instrument.
In the figure we have the way to use a low-cost digital clock chip to trigger an alarm. The...
This circuit is the traditional 555 oscillator that produces a hum in the piezoelectric...
This circuit was found in a computer publication from the 1970s. The transistors can be the BD135...