PC uses LPT port to turn on light - problem at boot time

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Jimmy Neutron

I've put some simple electronics to turn a on a light when the pc is turned on. I
am uses LPT port to to find out (a couple of relays & such) to turn the light on.
Unfortunately LPT ports power turns on and of a few times before the boot inget
around this problem? Tried USB but it has the same problem.
 
Jimmy said:
I've put some simple electronics to turn a on a light when the pc is turned on. I
am uses LPT port to to find out (a couple of relays & such) to turn the light on.
Unfortunately LPT ports power turns on and of a few times before the boot inget
around this problem? Tried USB but it has the same problem.
Click to expand...

If you connect to +5VSB, that would be active whenever the switch
on the back of the computer is engaged. I don't think you want
that.

When you push the power button on the front of the computer,
the power supply main outputs should come on. +5V would be
one of those outputs. You could extract +5V from a hard
drive connector. The voltage should be "solid" for the
length of your computing session. When you put the
computer to sleep (standby suspend to RAM), then the
+5V is turned off. That one shouldn't blink out, because
if it did, your computer would crash.

It is possible the power on the ports, like the ones
you've tested, is controlled by a switch (MOSFET) on the motherboard.
That may be for the purposes of "backfeed cut", or preventing
an external source of power from leaking back into the
computer. I cannot say anything about that with respect
to my own computers, as I've never tested for it.

I suspect if you use a disk drive connector for the function,
you'll get better results.

Paul
 
Paul said:
If you connect to +5VSB, that would be active whenever the switch
on the back of the computer is engaged. I don't think you want
that.

When you push the power button on the front of the computer,
the power supply main outputs should come on. +5V would be
one of those outputs. You could extract +5V from a hard
drive connector. The voltage should be "solid" for the
length of your computing session. When you put the
computer to sleep (standby suspend to RAM), then the
+5V is turned off. That one shouldn't blink out, because
if it did, your computer would crash.

It is possible the power on the ports, like the ones
you've tested, is controlled by a switch (MOSFET) on the motherboard.
That may be for the purposes of "backfeed cut", or preventing
an external source of power from leaking back into the
computer. I cannot say anything about that with respect
to my own computers, as I've never tested for it.

I suspect if you use a disk drive connector for the function,
you'll get better results.

Paul
Click to expand...


Oh bummer! Some times I get 3 blinks and othertimes two. When my program load is
the light already on. Using other connection is a bit of a hack I'm trying to
avoid. If I replace the unit (PC) I won't know what kind of cycle there is.
 
Jimmy said:
Oh bummer! Some times I get 3 blinks and othertimes two. When my program load is
the light already on. Using other connection is a bit of a hack I'm trying to
avoid. If I replace the unit (PC) I won't know what kind of cycle there is.
Click to expand...
Just use a diode and a 500 ufarad electrolite,that will remove
the blincks.
 
Jimmy Neutron said:
I've put some simple electronics to turn a on a light when the pc is
turned on. I
am uses LPT port to to find out (a couple of relays & such) to turn the
light on.
Unfortunately LPT ports power turns on and of a few times before the boot
inget
around this problem? Tried USB but it has the same problem.
Click to expand...

It's hard to understand your question, either due to a language issue, or
due to sloppy writing.

Jon
 
Sjouke Burry said:
Just use a diode and a 500 ufarad electrolite,that will remove
the blincks.
Click to expand...

I got it figured out. I use two 5V relays and some relay logic.
 
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