We found this frequency meter circuit in a 1974 documentation. The circuit is powered by 12 V and has 8 digits. Changes can be made using a prescaler to reach higher frequencies.
This TTL circuit for digital signals up to a few dozen megahertz was found in old documentation, but...
This circuit with an operational amplifier was found in the magazine Radio Electronics of...
This detector is from the 1990 Motorola Dataar Databook, but can be adapted to work with more...