How to wire LEDs through magnets?

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  #1  
Old 06-24-13, 09:06 PM
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How to wire LEDs through magnets?

I'm designing a lamp that will be made up of multiple, modular pieces of plywood. Each piece will contain an LED light and the needed wires. The idea is to have a base that plugs into a socket. And the plywood pieces attach to the base and to each other with magnets. This enables the user to assemble and configure the light to his wants and needs.

But I have never wired anything before... (Slight problem when designing a lamp haha.)

How do I wire this thing so that the LEDs light up only when connected to the base or to another piece itself in contact with the base?

I feel like their should be a way if there's a contact at each connecting point (magnet).

I have no clue about electrical wiring or where to begin.


I found this lamp which is similar to what I am trying to do if this helps visualize my question at all:
Branch Light - a modular LED light system | Bruno Fosi

Here is another similar example:
Crystal Light by Qis Design | Modern Baby Toddler Products - Plioz
6 days ago

And another: light blocks

I was told the LED module will need a current limiting resistor in it. Do I put one resistor in the first module that plugs into the current and thats it for the whole system? Or do I need a resistor in each module?

Thanks for any help you can provide...
 
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  #2  
Old 06-24-13, 09:34 PM
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Welcome to the forums.

m2tc ....... This is kind of a complicated problem so that rather then have two duplicate threads running on the same topic....we'll just use this one.

LED's require two wires to make them work. So do you want to assemble a chain of blocks so that they form a series loop or do you want each piece to light up as it is connected ?

I have a feeling you'll want each piece to light up independently. That will require at least two magnets per piece and four if you want to be able to connect additional ones to each piece. It will require the use of diodes so that there is no attention needed to correctly orient the piece with respect to DC polarity.

I was looking at some of the links you left.... they seem to use a custom contact plate and a single magnet for connection. I can help you with the wiring but you're going to have to scout up the contact plates you want to use.
 
  #3  
Old 06-24-13, 10:26 PM
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Hi.

Thanks for the reply.
My idea was that you have the first module light up when you plug it into the socket. Then every time you add another module, that one lights up and the first one stays on. So that the more modules you attach together, the brighter it gets kinda thing.

I can find magnets and and other supplies to fit my design on my own.

What I really need help with is how to wire each module (keeping in mind they should all be the same if possible) and things like how many resistors I need and where they should go. I have never wired anything before so its a learning experience for me.

Whatever help/information you can provide, or if you can guide me to somewhere where I can learn this stuff myself, I would be extremely grateful.

Thanks again!
 
  #4  
Old 06-24-13, 11:22 PM
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I don't really know where to send you for help. This stuff is kind of custom and avant-garde.

You would need a low voltage power supply to run the LED's. Wouldn't have to be very big. Actually you could use a wall wart for power.

Here's the thing.....if you use a wall wart for power.....that unit is UL listed and you can use any type of wiring in your fixture. If you bring 120 vac into your fixture then you need to things a certain way.
 
  #5  
Old 06-25-13, 12:09 AM
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A wall wart would be fine. i was told that i would need to have contacts that mate at the end of each block. All ends should be intermatable. Each end needs two contacts + and - or + and ground. I was also told that the LED module will need a current limiting resistor in it. And that i should run 12 volts thru the whole system.. But not sure how reliable source was. Does that sound right?
 
  #6  
Old 06-25-13, 06:34 AM
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Here's an LED resistor calculator you can use for single LED circuits. Other calculators are out there for multiple LED chains.

If you want the modules to be able to be connected to power through magnets, you can get around the polarity issue by using a 12 volt AC (not DC) wall wart. Each module will then need a diode or preferably a small bridge rectifier.

Technically LEDs are diodes and as such they will light using AC power. However, the reverse voltage is critically important. For a 12-volt AC power supply the LED must have a reverse voltage spec above 17 volts.
 
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Old 06-25-13, 07:44 AM
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Rick, a bridge rectifier in each module is a good idea. It will basically eliminate the need to keep track of positive and negative whether or not you use a AC or DC power supply.

I would build something like this:
Name:  IMG_0921.JPG
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The diamond diode is a bridge rectifier (all one package). The resistor needs to be sized based on the LED (see Rick's calculator). You could build as many of these as needed. The power supply would just need to be large enough to run all of them (which shouldn't be an issue until you start getting a number of them together).

I would build this first and try it out. The harder part will be to have two copper plates make a good connection when these pieces are connected together. Often times the electronics are the easy part, the mechanics are more difficult.
 
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Old 06-25-13, 06:06 PM
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Oh my god you guys are awesome, so helpful
I can't wait to actually start trying some of this stuff out!
It just occurred to me yesterday, will people get an electric shot if they touch an exposed magnet? Haha I never thought of that... It may be a stupid question.

Anything else I should know/avoid doing?
 
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Old 06-25-13, 08:04 PM
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You are using low voltage so the chance of a shock are extremely low. If this is going to be accessible to kids then we need to know that. The voltage would need to be made even lower.

I was looking at your second link again and it shows the lamp in a kids room. Not sure if it's considered a toy. The problem with kids is that they could lick the contacts on the cube
 
  #10  
Old 06-25-13, 08:09 PM
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The lamp is for a furniture competition, I'm an architecture student. So kids may touch it but its not intended as a kids toy or anything like that. It will be on show and people will be able to play and reconfigure it.
 
  #11  
Old 06-26-13, 05:59 PM
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What kind of wire do I buy to start figuring out all of this and playing around with it?
 
  #12  
Old 06-26-13, 07:03 PM
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Any kind of wire would be fine. I would use a stranded wire maybe around 22 gauge. You're dealing with very low current so if you have small gauge wire laying around that would be fine.

If you have any of those old wall warts that are no good...... use that wire.
 
  #13  
Old 07-11-13, 04:57 PM
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Hey guys,

What do you think about a magnetic reed switch? would that possibly work?
 
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Old 07-11-13, 07:15 PM
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What do you think about a magnetic reed switch? would that possibly work?
For what?

.
 
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Old 07-11-13, 07:42 PM
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What do you think about a magnetic reed switch? would that possibly work?
I assume you mean that a reed switch would basically turn on/off the terminals when each section is connected. It definitely would work, but I think the mechanics of it might be difficult. I would probably start without the reed switches. With the low voltage that you're dealing with, unless someone licks their fingers first, it shouldn't be an issue.

Start simple, then upgrade from there. You already have quite a project on your hands.
 
  #16  
Old 08-28-13, 09:06 PM
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wire gauge.

Hey guys,

so the design of my lamp took longer than I expected. But I am finally done. Iwent to home depot to pick up some wires, LEDS etc just to start playing around with this thing and figuring it out. But I had no idea of what gauge wire to get. Any suggestions into how I can figure this out? Would 16 work? or 18?
 
  #17  
Old 08-28-13, 09:11 PM
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#18 or # 20 should work fine for you.
 
  #18  
Old 09-02-13, 04:31 PM
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So I tried this and it works in one module:
12V +----|>|----|>|----|>|---/\/\/----+ R = 22 ohms
12V +----|>|----|>|----|>|---/\/\/----+ R = 22 ohms
where you have 2x3 array of LEDs per module

Basically I would have 6 LEDs, one per side of the hexagon.

and I'm thinking of using Neodymium magnets since they are coated with a thin layer of metal so they conduct electricity. (I haven't tried these yet, still looking around to order some)

What I am unsure of is wether I can make each piece the same? or will I have problems once they are all assembled? I plan on having 8 modules total.

once stacked, they will ultimately look something similar to this: http://cdn.archinect.net/images/1200...e95bqhmcjd.jpg
but with the middles cut out because the inner ring is what is going to be lit up.
 
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Old 09-02-13, 07:28 PM
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There is a problem with your link.

I would think you'd want all the modules identical.
 
  #20  
Old 09-02-13, 09:26 PM
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hello move2thecity,

Have you come up with a way to use the magnets as circuit connections? The magnets that you are talking about are plated with a very thin coat of steel and will be a challenge to solder to (and for many other reasons aren't used as electrical conductors). I have seen several applications where a magnet (or magnets) are used to make a mechanical connection, but there are separate "pogo" pin or spring connectors that carry the electricity, so if the magnet idea doesn't work you might want to look in that direction.

Everything looks good as far as your schematic goes, if the LEDs have a Vforward of 3.8 volts and you wire 3 in series with a 22 ohm limiting resistor you are driving the LEDs each at:

I = V/R = (12 Volts - (3.8 volts + 3.8 volts + 3.8 volts)) / 22 ohm = 0.028 Amps.

Small LEDs are typically driven at 20 mA (0.020 Amps) so you're in the ballpark, but make sure you add up the Vforward of all the LEDs and choose a resistor that limits them to their designed limits (the lower the output, the longer the life). Vforward will be different for different color LEDs, Red LEDs are ~2 volts, Green ~3 volts, Blue/White ~4 volts.
 
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Old 09-02-13, 09:43 PM
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You can use the rare earth magnets with a hole in them like we use for alarm installations. The only problem is that the magnets won't stick/attract to each other so you may need to use the magnets and a steel plate for the connection. You can wrap the wire around the screw you use to fasten the magnet.

Rare Earth Magnets with center hole at eBay
 
  #22  
Old 09-08-13, 04:59 PM
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You guys are all awesome! Thank you so much for helping out... I haven't yet figured out the whole magnet connection that doubles as a contact point yet. I have been practicing playing around with these electrical circuits as I had never wired anything before and I have being milling test pieces of my modules out of plywood. The ring magnets might be a good solution to my problem. I'll order some and try them out! I'm also trying to design some kind of cover so that people won't touch the exposed contact points. I know some of you had said the current wouldn't be strong enough to shock someone but I figure I might as well be on the safe side....
I'll let you guys know how it turns out
 
  #23  
Old 09-08-13, 05:28 PM
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Would this work? The "Build-Your-Own Encased Magnets"

McMaster-Carr
 
  #24  
Old 09-08-13, 05:29 PM
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I was trying to think of ways to cover the contacts but you can't or they won't make electrical contact.
 
  #25  
Old 09-09-13, 07:46 PM
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Yeah, they would have to be removable. So that they cover the contact and then you remove the "caps" when you want to add another module on.
 
  #26  
Old 09-09-13, 08:42 PM
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Those magnets listed at McMaster-Carr are definitely worth looking into.
 
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