Electrical Engineering - Hobby Lighting

Author

Hobby Lighting

Mike

2006-01-16, 4:21 pm

(pardon for the repost, can't seem to respond and have to post as new)

Thanks for your help. I took a quick look at the doll house lights but
don't see a type of light that I'd want. The LEDs sound good and I can
solder but don't know enough about what to purchase and how to configure it.
I'll explain what we want.

My son built the Coninental Airlines Arena (where the NJ Devils play). It
looks great and has see through panels so you can see inside but it is dark.
It is about 2' x 3'. We'd like to have some lighting underneath the roof
and also some lighting around the outside of the arena. These need to be 2
separate runs since the entire roof (and lighting) can come off to really
look inside. How many LEDs do you think would be needed for this inside
portion? Can they be setup with a on/off switch and batteries so that we
would not need to plug it in? I would need to know also about any other
issues and where to put what (i.e. resistors as you mentioned). If this is
too much to ask, do you think I could get the info at the Radio Shack?

Thanks again.

"Beachcomber" <not_real@xxx.yyy> wrote in message
news:43cbed6a.8103203@newsgroups.comcast.net...
> On Mon, 16 Jan 2006 14:36:44 +0000, =?UTF-8?B?UGFsaW5kcuKYu21l?=
> <sb382638@hotmail.com.invalid> wrote:
>
>
> Last time I was in a hobby shop (which I admit was a long time ago)
> they use to sell "pea" lamps for model railroaders. At the time, it
> was the smallest light you could get and they were pretty bright too.
>
> Rather than cut up a Christmas Tree light string, if you have just a
> bit of soldering skill I would recommend purchasing individual LED's.
> Radio Shack has them fairly cheap. Companies like Jameco Electronics
> and MCM Electronics have them for even cheaper.
>
> You can run them off of standard DC voltages (from a plug in DC power
> adapter) like 12 Volts, 9 volts, or 6 volts, but you do need to put a
> dropping resistor in series with the LED to keep it from getting too
> high a voltage and burning out.
>
> The value of this resistor is fairly easy to calculate. Maybe someone
> here can show you how to do it.
>
> The advantage of LED's is that they run cool, last for tens of
> thousands of hours (if you limit the current properly), come in just
> about every color available, use very little current, and are
> available in high-brightness versions, if desired.
>
> Beachcomber
>
>

Beachcomber

2006-01-16, 5:21 pm

On Mon, 16 Jan 2006 14:42:31 -0500, "Mike" <m@a.com> wrote:

>(pardon for the repost, can't seem to respond and have to post as new)
>
>Thanks for your help. I took a quick look at the doll house lights but
>don't see a type of light that I'd want. The LEDs sound good and I can
>solder but don't know enough about what to purchase and how to configure it.
>I'll explain what we want.
>
>My son built the Coninental Airlines Arena (where the NJ Devils play). It
>looks great and has see through panels so you can see inside but it is dark.
>It is about 2' x 3'. We'd like to have some lighting underneath the roof
>and also some lighting around the outside of the arena. These need to be 2
>separate runs since the entire roof (and lighting) can come off to really
>look inside. How many LEDs do you think would be needed for this inside
>portion? Can they be setup with a on/off switch and batteries so that we
>would not need to plug it in? I would need to know also about any other
>issues and where to put what (i.e. resistors as you mentioned). If this is
>too much to ask, do you think I could get the info at the Radio Shack?
>
>Thanks again.
>

Calculating the dropping resistor for an LED circuit is really not
complicated.

I found a site that may help you. The circuit is just a battery (or
DC output plug in supply), a resistor, a LED, and maybe a switch, all
in series with each other.

http://www.theledlight.com/resistancecalculator.html

LED's are polarized (+ -) so if you hook them up backwards, nothing
bad happens... they just don't light up.

Most LED's require 0.20 ma and anywhere from 2.0 to 3.5 volts. The
packaging should have this information.

Then you look at your power supply voltage. Let's say you have an
LED that needs 2.0 volts and a power supply battery that puts out 6
volts. That means your resistor needs to drop 4 volts (6 - 2) = 4
volts.

By ohms law, your resistor should be 4 / 0.20 = 200 ohms

The power dissipated by the resistor will be I^2 x R or 0.20 x 0.20
x 200 = .08 watts so a common 1/4 watt resistor (0.25 watt) will
work just fine.

Beachcomber

Palindr☻me

2006-01-16, 5:21 pm

Mike wrote:
> (pardon for the repost, can't seem to respond and have to post as new)
>
> Thanks for your help. I took a quick look at the doll house lights but
> don't see a type of light that I'd want. The LEDs sound good and I can
> solder but don't know enough about what to purchase and how to configure it.
> I'll explain what we want.
>
> My son built the Coninental Airlines Arena (where the NJ Devils play). It
> looks great and has see through panels so you can see inside but it is dark.
> It is about 2' x 3'. We'd like to have some lighting underneath the roof
> and also some lighting around the outside of the arena. These need to be 2
> separate runs since the entire roof (and lighting) can come off to really
> look inside. How many LEDs do you think would be needed for this inside
> portion? Can they be setup with a on/off switch and batteries so that we
> would not need to plug it in? I would need to know also about any other
> issues and where to put what (i.e. resistors as you mentioned). If this is
> too much to ask, do you think I could get the info at the Radio Shack?

There are dozens of web pages devoted to LEDs and how they work and how
to use them, for example:

http://www.theledlight.com/LED101.html

A Google search will find far more.

An alternative for generating many pin-points of lights (eg Starship
Andromeda style) is to use fibre optics. Buy a cheap "mare's tail" fibre
optic desk lamp and redeploy a number of the fibres, spreading them to
where the lights are needed but using a single light source to "power" them.

They will run for many hours off a battery. Even if an incandescent lamp
is used instead of an LED.

For area illumination, rather than point sources of light, you may want
to check out cold-cathode kits. They are fitting them in (well, mostly
under) cars and computers. You would need a bigger battery though.

For low levels of "atmospheric" lighting, you might want to check out
electroluminescent cable. It uses very little power and can be very
effective.

--
Sue

[color=darkred]
>
> Thanks again.
>
> "Beachcomber" <not_real@xxx.yyy> wrote in message
> news:43cbed6a.8103203@newsgroups.comcast.net...
>

VWWall

2006-01-16, 6:21 pm

Beachcomber wrote:
> On Mon, 16 Jan 2006 14:42:31 -0500, "Mike" <m@a.com> wrote:
>
>
> Calculating the dropping resistor for an LED circuit is really not
> complicated.
>
> I found a site that may help you. The circuit is just a battery (or
> DC output plug in supply), a resistor, a LED, and maybe a switch, all
> in series with each other.
>
> http://www.theledlight.com/resistancecalculator.html

This requires current entries in mA. May be confusing!
>
> LED's are polarized (+ -) so if you hook them up backwards, nothing
> bad happens... they just don't light up.
>
> Most LED's require 0.20 ma and anywhere from 2.0 to 3.5 volts. The
> packaging should have this information.

That should be 20 mA or O.020 A.
>
> Then you look at your power supply voltage. Let's say you have an
> LED that needs 2.0 volts and a power supply battery that puts out 6
> volts. That means your resistor needs to drop 4 volts (6 - 2) = 4
> volts.
>
> By ohms law, your resistor should be 4 / 0.20 = 200 ohms

NO! Ohm law requires R in ohms, I, (current), in Amperes, V in Volts.
This would be: 4/0.020 = 200 ohms (Right answer, wrong math!)
>
> The power dissipated by the resistor will be I^2 x R or 0.20 x 0.20
> x 200 = .08 watts

Actually, 0.20 x 0.20 x 200 = 8W (But the current is 0.02 A so: 0.02 x
0.02 x 200 = 0.08)

so a common 1/4 watt resistor (0.25 watt) will
> work just fine.

Right answer, wrong math.

Checking by: W = E x I = 4 x 0.020 = .08 W

--
Virg Wall, P.E.

TimPerry

2006-01-17, 2:21 am

"Mike" <m@a.com> wrote in message
news:43cbf5a9$0$31366$6d36acad@roc.nntpserver.com...
> (pardon for the repost, can't seem to respond and have to post as new)
>
> Thanks for your help. I took a quick look at the doll house lights but
> don't see a type of light that I'd want. The LEDs sound good and I can
> solder but don't know enough about what to purchase and how to configure
it.
> I'll explain what we want.
>

as you can see there are a lot of options. let me throw out another idea.
each of the xmas light bulbs probably is 2.5 volts ( see
http://people.howstuffworks.com/christmas-lights.htm )

you simply obtain a power supply, either AC or DC at some voltage... the
easiest to come by is probably 12 to 13.8. next cut sections of bulbs say 5
or 6 depending on how bright you want them to be. and then keep adding
'zones'

the advantage here is you have a "safe" 12 volts running through the project
instead of 120.

a rough estimate of .5W @ 2.5V = gives .2 amp per 'zone'

a fuse for each zone might come in handy (see the shunt thingy in xmas
lights) i would pick 1/2 A as a nice common value.

good luck and post a pic somewhere when its done

LinkBot