We found this circuit in a 1973 publication. The circuit lets frequencies below 480 kHz pass through with an output impedance of 1k. The circuit can be implemented with current operational.
We found this 3-digit digital odometer for bicycles (or another application) in a 1995...
This circuit was published in a 1977 English magazine, but remains current, since we can assemble it...
In the figure we have the configuration of series regulator protector suggested by Motorola in 1968...