Modern Blinkenlights

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Sat Jun 19 16:33:16 2004

> 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
Received on Sat Jun 19 2004 - 16:33:16 BST