Reciprocal frequency counter

Alan built a reciprocal frequency counter. What sets reciprocal counters apart is that they adjust to the signal measured, sort of an auto-ranging feature.

It is AVR based and automatically enables or disables a prescaler to handle frequencies from 0.5 Hz to 100 MHz. It can give the same precision whether the signal is fast or slow…

[I have a] question about the front end. I’ve tried various input circuits, I’ve tried biasing inverters, schottky inverters, etc. I want the input to support even measuring mains voltages if possible.

Any suggestions for Alan?

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  1. I presume you want auto-ranging….. I presume you want an isolated ( ~1KV ) differential input that is good from .5Hz to 100MHz. Once we specify the functional requirements we can design the front end.

  2. Hello Gus,
    I don’t recall if he specified what main line voltage he has. He gives more details in the forum post. First link in the paragraph, and if you have issues with the color scheme its the first sentence.

      1. From what I understand, it adds phase detection to the start and end of the sample interval, to increase the resolution of the sample. Just the thing to add to a frequuency counter chip.

        I found the FC-501 on Github, but the docs are in Russian and seem to lack detail.

  3. Yep, that’s the one. Github version of files is at:
    Go to the doc subdirectory, find instructions – in Russian.

    There are Altera and AutoCad directories, and lots of photos of the front panels – but no actual schematics. Your link is much better, thank you.

    The 501 / 510 was just a typo. However, since a sawtooth is the integral of the area of a pulse, I really thought it was “integrating”. rather than “interpolating”.

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