Found in Exar documentation from the 1980s, this circuit has a 60 dB cutoff at 1800 Hz. The circuit can be adapted to operate at other frequencies.
The CMOS 4046 integrated circuit is not very common today, consisting of a very efficient PLL for...
In the circuit shown in the figure to the side, the relay is activated when the light stops...
With this name, the English publication where we found this circuit indicated a sensitive touch...