| Author |
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dmm
Guest
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 Posted:
Fri Mar 18, 2005 3:14 pm Post subject:
Re: How much current does an LED take? |
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On Thu, 17 Mar 2005 14:57:23 +0800, "Sea Squid" <Sea.Squid@hotmail.com> wrote:
| Quote: | I want to experiment the parallel port with eight LEDs tied to
a cut parallel port cable, then send instructions with Visual Basic
to create some patterns. Is there any danger to my laptop?
Thanks.
|
I highly recommend a book by Paul Bergsman
"Controlling THe World With Your PC"
ISBN 1-878707-15-9
Also,have a look at
http://www.boondog.com
..
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Don Klipstein
Guest
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| Posted:
Sun Mar 20, 2005 7:29 am Post subject:
Re: How much current does an LED take? |
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In article <423962ee$1@news.starhub.net.sg>, Sea Squid wrote:
| Quote: |
"Active8" <reply2group@ndbbm.net> wrote in message
news:95w78i1wjhys$.dlg@ID-222894.news.individual.net...
On Thu, 17 Mar 2005 15:00:59 +0800, Sea Squid wrote:
I found PP is unable to drive such LEDs, which needs 20mA, but what is
the
converter chip I shall order?
It is? I thought PP used TTL outs. You should be able to drive an
LED through a current limiting resistor. Is it backwards? Does the
printer still work? Can you light the LED with a battery or whatever
and a resistor? Are you sure VB and your OS will let you write the
port? What is the Vf of your particular LED?
It is the convention to cascade an LED with a resister. PP can only provide
approximately
1mA current. This current is insufficient to drive an LED,
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I know LEDs that glow almost bright enough to put a spot in your eyes,
although these are high-brightness high-efficiency LEDs whose
efficiencies are favored by low currents.
I have in mind two green models by Nichia:
NSPG520S - a green one in a 5 mm package with a nominal beamwidth
("viewing angle") I believe 45 degrees - the widest really common viewing
angle in a 5 mm round-tip "bullet" non-diffused package. Should be almost
"nice-and-bright" at .125 mA, although I have experienced an
"unreliability" at currents this low that is mostly just a significant
variation in brightness from one unit or one lot to another when the
current is so low.
NSPGF50S - a small rectangular one with "viewing angle" around 110
degrees - very wide angle. Viewing angle is more like 140-150 degrees if
you allow brightness into directions so far off axis to be "valid" if
about 1/4 that of the on-axis brightness. I consider these "adequately
bright" at about .2-.25 mA.
In my experience, both of the above models as well as most other InGaN
"regular size" LEDs have brightness adequate to "downright bright" with
reasonable reliability at .5 mA. Even most "cheapest" InGaN LEDs at 1
(maybe as much as 2 in worse cases) mA are brighter than most LEDs of
vintage 1982 or older are at 20 mA.
Anyone wanna compare a 1976 vintage "prime grade" green LED at 20 mA to
a modern green one by Nichia (or a competitor such as ETG) with similar
viewing angle and being run at .5 mA?
As for small quantity purchasing: http://www.nichia.com, and look for
"order online"
- Don Klipstein (don@misty.com) |
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Active8
Guest
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| Posted:
Sun Mar 20, 2005 2:41 pm Post subject:
Re: How much current does an LED take? |
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On Sun, 20 Mar 2005 07:29:19 +0000 (UTC), Don Klipstein wrote:
| Quote: | In article <423962ee$1@news.starhub.net.sg>, Sea Squid wrote:
snip
It is? I thought PP used TTL outs. You should be able to drive an
LED through a current limiting resistor. Is it backwards? Does the
printer still work? Can you light the LED with a battery or whatever
and a resistor? Are you sure VB and your OS will let you write the
port? What is the Vf of your particular LED?
snap - devil's scissors - Christopher Wagner, Faust
Anyone wanna compare a 1976 vintage "prime grade" green LED at 20 mA to
a modern green one by Nichia (or a competitor such as ETG) with similar
viewing angle and being run at .5 mA?
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No. I understand some of the high efficiency LEDs are great. I'm
still waiting to hear more about the OP's PP that can't handle more
than 1 ma. :) My troll meter's going haywire.
--
Best Regards,
Mike
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Sea Squid
Guest
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| Posted:
Mon Mar 21, 2005 6:10 am Post subject:
Re: How much current does an LED take? |
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| Quote: |
NSPG520S - a green one in a 5 mm package with a nominal beamwidth
("viewing angle") I believe 45 degrees - the widest really common viewing
angle in a 5 mm round-tip "bullet" non-diffused package. Should be almost
"nice-and-bright" at .125 mA, although I have experienced an
"unreliability" at currents this low that is mostly just a significant
variation in brightness from one unit or one lot to another when the
current is so low.
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Thank you for the information, but graph titled "Forward current vs relative
luminisity"
showed the current scale is from 0 ~ 120mA, so maybe it still needs a 20mA
to get a resonable light.
Are you sure that 0.125mA can light it up? |
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