Re: [CAD_CAM_EDM_DRO] Capicitor tuning VCO/DRO

On Wednesday 12 May 2004 07:37 pm, Bill Vance wrote:

> >I have some of those chips (the original numbers), but have never done
> >anything with them. They were used in later production runs of the
> > Commodore 64 computer... :-)

> I've heard they were used in some of the earlier IBM clones with some other
> part number, too.

News to me...

> Assuming we're still talking dual VCOs, and not 14 stage ripple counters,
> you may have just made a sale. I wish they were the faster LS series, but
> at least these would be good for initial testing. Care to part with some
> of them?

Sure, I'll have a look see what I have on hand and get back to you offlist...

<...>

> >Do you have any sort of values in mind for what the acceptable range is
> > going to be?

> Not precisely, but I do have a formula for figuring with.
>
> C=300/f Where C is in microfarads, and f is in Hertz.

> From the info I've managed to glean about these chips, the original MC4024
> topped out at about 20 MHz, and the 74424/74LS424 went up to 25/30 MHz
> respectively.

Note that those are minimum guaranteed specs, individual parts may do better.
And a lot is going to depend on circuit layout and design when you get up in
that range.

> >> I'm pretty sure this would require shielding, which might affect things,
> >> too.

> >If it does require it, then it sure will -- it'll likely increase stray
> >capacitance all over the place. In any event, it's going to require some
> >mighty careful construction...

> I figure two kinds; Something to keep oil/coolent/swarf off the works,

Moving it out of harm's way and using a mechanical linkage might work, too.

> and maybe some sort of shield braid over that to shield the vari-cap from
> outside noise. This might not be needed for a hand crank mill, but might
> for a CNC unit.

I guess that depends on the noise in your environment. And noise in that
application (capacitor for a VCO) is going to cause some jitter in frequency
or phase, but not do much else, so reading it over a period of time and
averaging things out should take care of that problem.

> The basic idea is to use insulated mounts to attach the wire or tube to the
> table, and the other to the platform the table is mounted to. The length
> of the wire and tube being roughly equal to the table travel, and the
> output frequency being counted for positional readout. Additional
> circuitry/counter chips for setting the zero, etc.

I can't quite picture it, but I have that difficulty with a lot of what I
see discussed in here. If you get it working post pictures somewhere! :-)