232 Frequency Detector Module

This photo is of a clone of a 232 Frequency Detector prototype module.  This is a frequency to voltage converter based on the schematics, but I do not believe the schematics quite follow this block diagram.


This is my best guess at this module based on a casual look at the schematics.

The signal leveler is automatic gain control (AGC) circuit which provides a constant amplitude output. There is no sensitivity control shown on the schematic. The Transfer Gate simply mirrors the gain of the AGC for an independent audio channel. The tracking filter reduces the input signal to it's fundamental frequency.

This fundamental frequency goes through a comparator to generate a square wave output which is +/- 2V. This is an audio level which should be a 3.5mm jack and might be the Pulse output. It isn't driven by an envelope detector per the panel diagram.

Pulses are derived from the rising edge which generate an average CV which drives a ramp core VCO although there is no output shown on the schematic. The phase lock is derived since the pulses from the fundamental are what resets the ramp core. This VCO feeds a S&H circuit through some complex circuitry to generate a filtered CV output corresponding to the frequency.

This clone never operated correctly, likely due to errors on the schematic. This is one strange design.