Re: PATCH : LEDs - possibly the most pointless kernel subsystem ever

["Herbert Pötzl" <herbert@13thfloor.at>]

On Wed, Jul 30, 2003 at 07:44:57PM +0200, Pavel Machek wrote:
> Hi!
> 
> > > But this kind of blinkenlights needed pretty fast LEDs. (At 486 time
> > > I decided that parport on ISA is fast enough..)
> > 
> > I'll buy some LEDs and build a parallel port connected LED panel
> > tomorrow...  Do you think the overhead of driving the LEDs would have
> > too much of a negative effect on system performance?  If so, or if
> > we
> 
> I'm not sure. At 486 days I was pretty sure it did not matter. These
> days you might get 10% slowdown on some microbenchmark, or something
> like that. I do not think it can slow down common tasks.
> 
> My construction of LED lights is extremely flaky, and I'm afraid of
> burning printer port. At 486 days ports were expected to survive such
> abuse. Not sure if todays EPP/wtf ports can handle that.

parport uses 5V (actually a little less) so if you
use normal (not extra super duper bright) leds and
put a 1kOhm resistor in front of each led, then it
will drain 5mA per led, which gives a total of 40mA
for eight leds (for example)

now for the parport: depending on the technology
and the age of the circuit, it provides between
2 and 14mA output at >2.4V (the led usually requires
less than 1.5V to operate) so this would be within
the range ... but, if you want either extra brightness
or extra security, you could provide +5V and use
the outputlines as sink, which then is between
15 and 25mA ...

anyway, parport should be short circuit safe, so
the worst what could happen is, that the leds are
not working ;) ...

HTH,
Herbert

PS: I usually use 220Ohm and no external power ...

> -- 
> Horseback riding is like software...
> ...vgf orggre jura vgf serr.
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