Found in a 1965 Electronic Design, this circuit can be made with modern equivalent transistors. The capacitor basically determines time.
In the diagram we show how to divide the frequency by multiples of 10 using several CMOS...
This circuit was found in a 1982 Maplin publication. The circuit is tuned to recognize a 400 Hz...
In the figure we have another application for the LT3518 integrated circuit from Linear Technology...