19 Jun
2004
19 Jun
'04
9:33 a.m.
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
Err, is it beyond thw wit of modern designers to decode a 4 bit value
to drive 16 LEDs using a purely digital circuit.
you some combination of 0-15 or 0-16 or 1-16 LEDs per
channel (I haven't
Every LED bargraph chip I've seen drives 10 LEDs.
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
This is not exactly hard to design. To do it purely digitially, you can
use a 4 line to 16 line decoder (e.g. a 74x154) if you want 'dot' mode.
To do 'bar' mode, it's a simple exercise to design the logic, and if you
like burn it into a PAL (or PROM, or...).
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
Not it isn't IMHO...
I suppose if you want to multiply an 8 bit value by 3, you'd put it into
a DAC, then into an op-amp configured as a *3 non-inverting amplifer,
then into an ADC, right?
for the job. What I can't remember is what the
common part number is
(it's something like LM3xxx).
LM3914 for the linear one. There's also the LM3915 and LM3916 which have
various flavours of logarithmic scale.
-tony