[sdiy] Idea for tuner/display

[Magnus Danielson]

From: Paul Perry <pfperry at melbpc.org.au>
Subject: Re: [sdiy] Idea for tuner/display
Date: Tue, 28 Jan 2003 00:09:21 +1100

> Slightly related, I would like a simple digital
> way to indicate which of two square waves have
> the highest frequency.
> I know there must be an easy way.. but, I'm not the guy to find it!

You should look at the PFD (Phase-Frequency Detector) of the 4046.
The Philips datasheets are pretty good (look at the 7046 and 9046 for de luxe
variants).

The PFD uses several flip-flops and provide two outputs: U (Up) and D (Down)
and in the 4046 these control two transistors, so that you get a chargepump
which pulls your cap up or down. Should work pretty well for your problem.

Cheers,
Magnus