On Fri, Jun 18, 2004 at 09:59:16PM +0100, Tony Duell wrote:
> > I don't know the one he's talking about but the most popular one all over
> > the web (and the one that i've got lying around from my old mail server)
> > just has 10 LEDs driven directly from the port with a common resistor.
>
> If that's how they did it, then it's a lot more reasonable.
That works fine for showing load on a single CPU. The circuit I saw that
emulated the BeBox double-bargraph is coming back to me now - *two* 4-bit
resistor-ladder D-As and a bargraph generator chip for each, tune to give
you some combination of 0-15 or 0-16 or 1-16 LEDs per channel (I haven't
seen a real BeBox up close, so I'm not sure how they look when they are
showing 'idle').
It's a harder circuit to make by hand than the simple 8 or 10-LED one
that's easy to find, but when you get it working, it _is_ more impressive.
Besides... for a simple load meter, there's no reason to be able to
individually address the dots - the LED bargraph chip is the right tool
for the job. What I can't remember is what the common part number is
(it's something like LM3xxx).
> And I'd probably add a buffer chip (something like an 'LS540 or 'LS541,
> whichever allowed me use it as a current sinking stage (LED + resistor
> returned to the +5V line). Most printer ports can supply the current
> needed be LEDs, but I'd not want to risk it, if that port was part of a
> difficult-to-find multi-IO chip on the motherboard. For PCs like mine,
> where the printer ports are all built from TTL on add-on cards, and where
> I have schematics anyway, I'd just connect the LEDs directly to the port.
I'd recommend a buffer chip, too - I tried adapting one of the bargraph
designs to run an analog panel meter, but only my desktop could source
enough current (TTL ISA parallel-port card)... my laptop couldn't budge
the needle.
I gotta say that an analog load meter is pretty cool.
-ethan
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Received on Fri Jun 18 2004 - 20:28:30 BST