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Magnetic Refrigerator Lights

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Turn your fridge into a canvas for LED art. Any passerby can place and relocate the magnetic LEDs any way they wish to create illuminated pictures and messages.

It's great for high traffic kitchens and It's fun for kids and adults alike.
 
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Step 1: What You Need

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Most of what you need can be found at local hardware and electronics parts stores or from online vendors.

Parts:

-Super Shield conductive nickel paint
This can be found at electronics parts stores. It's usually used to add RF shielding to plastic cases. We will be using it because it's electrically conductive.

-1/4" copper tape used for circuit board repair (optional)
If conductive paint can't be found, this may be a possible substitute. It may be a good idea to get some anyway as a way to repair any future scratches or chips in the conductive paint.

-Spray Paint
I used Krylon Fusion For Plastic because it sticks to almost anything, doesn't require a primer and has a nice finish.

-10mm LEDs in quantities and colors of choice
I used 20 LEDs of each Red, Green, Blue, Yellow and White. These can be bought online.

-330 Ohm surface-mount resistors
Get one for each 2.4 Volt LED (Typically red, orange, yellow and sometimes green LEDs are 2.4 Volts). The 3.6 Volt LEDs (typically blue, white, UV and true green) do not require resistors.

-One 4.5 Volt, 500 milliamp AC power supply
By using AC, the polarity of the LEDs won't matter. They will light up whichever way they are played onto the grid. This also reduces power consumption because the LEDs will run at a 50% duty cycle.

-1/8" diameter x 1/16" NdFeB Nickel plated disc magnets
Get two for each LED. These can be found online.

-1/4" diameter x 1/16" NdFeB Nickel plated disc magnets
I used six - two for attaching the power source to the fridge, and four more for making magnetic jumper wires to bridge the gap between the door and the side of the fridge.

-5 minute epoxy
Get the kind that you mix from clear and yellow tubes.

-Masking tape

-1/4" Quilter's tape
This is just masking tape but 1/4 inch wide, the thinnest tape I could find. You can find this in craft stores. Ideally, you want tape that is just slightly wider than the diameter of the magnets used on the LEDs.

-Solder


Equipment:

-Needle-nose pliers

-Small wire cutters or fingernail clippers

-Soldering iron or gun

-Wire wrapping tool or other tool with a flat round 1/8" diameter tip
It's really the 1/8" diameter we're going to use so you could use a grinded down dollar store screwdriver if that's what's available.

-X-acto knife

-Wooden toothpick

-The cap from a cheap pen

-Putty/Clay/Plasticene/Play-Doh
This is primarily for holding LEDs in place while you work on them.
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shadus7 years ago
What happens if you lick your finger and touch the grid across the lines?
That depends (partially) on the frequency of the AC wave.
Anything above several hundred Hz travels along the *surface* of your skin and is relatively safe (increase the voltage enough, and yes, it gets dangerous).
Anything lower than ~100Hz can travel through the core of the body, and is potentially lethal, even at low voltages (so i've read).
And to hurt yourself, you'd actually need to cross the circuit with *both* hands,
otherwise, you're just creating a circuit between two fingers. You might feel a tingle (we never have with ours), but you're not going to fry anything.
Note that i am neither an engineer nor a lawyer -- tinker with caution.

Voltage is not the determining factor in a lethal shock, amperage is. With the amperage extremely low, you are still able to push high voltage without causing permenant damage. This is what allow some tasers to output (advertised) 160,000V without being lethal. A 100 V @ 100 mA current has a higher chance of killing you than a 160,000 V @ 50 mA current. It only takes 100 to 200 mA to be lethal. Hope this helps clarify :)
The Taser has plenty enough current to kill, and the reason it doesn't is the contacts are not spread out to form a current across your heart. 50 ma passing through the heart will disrupt the heart and kill you. If the contact points of the Taser is spread to say contact one on each arm, then you're most likely to die.
It's not 100-200mA, its on the order of 40-50mA and if you were subject to 200mA you would be toasted and long gone...
A good way to think about it is pretend the current is a river where voltage is equal to the AMOUNT of water and amperage is equal to the SPEED of the water. A huge river moving extremely slowly is less likely to wash you away than a small river traveling extremely fast.
 Sorta, but not quite.  Usually when there is a water analogy, we think of water in pipes rather than in a river.  In that analogy, current is the amount of water flowing, and voltage is the pressure it's under.  

The components are usually represented like so:
  Resistors: plates with little holes in them or narrow diameter pipes.  The rate at which water that will flow is proportional to the pressure drop along the system.
  Diodes: One way valves.  You can think of the forward bias voltage as the pressure it takes to open the value at all.
  Batteries: A pump.
  Inductors: An impeller with a flywheel attached.  The bigger the inductor, the bigger the flywheel
  Capacitors: A rubber membrane.  Under pressure, it will stretch to hold some water, but ultimately no water passes through the membrane.

The list goes on.  Transistors can be thought of a little gate arrangements, so that a little flow on the "base" lifts a gate on a much larger flow between the "collector" and the "emitter". While far from perfect, it's a good enough analogy that there are people who actually build complicated circuits out of pipes and other parts.  They tend to be fascinating, but rarely useful.

  -- Mitch
With such a low voltage and low current, nothing will happen at all to anything living. The resistance of your skin is too great for any current to do damage.
raise the current high enough and 1 volt becomes dangerous.
Actually no, current is not the only thing that kills you. The voltage must be high enough, too because the voltage is how much 'push' the current has.

Ohm's law:

Voltage / Resistance = Max Current

resistance of skin = 1,500,000 ohms

5 / 1500000 = 0.0000033 Amps

You won't even feel that.

http://www.people.vcu.edu/~rgowdy/mod/086/imp.htm#4

! WARNING ! 50,000 OHMS INSIDE !
Intel Inside? No, resistance inside!
After thought:
Implying I'm thick? lol!
What area of skin is that, resistance per cm2 / cm3?
coderj shadus7 years ago
Just about nothing. It's very low voltage (4.5v), you would get more sensation from licking a 9v battery. You could possibly damage the transformer, but the resistance of the paint plus the saliva would probably keep that from happening.
sorry but licking a 9v?
Yea. thats how you see if they're dead or not. It doesn't hurt or anything, just tingles.
ahh i see but i use a volt meter
what a great observation! I wonder how many people do that? I bet you have to be a very certain kind of curious child to find that out, because you certainly don't learn it in electronics class.
its fun too! haha
Darkshot shadus6 years ago
let me guess a past "Learning experience"??? lol!
Malicah1 year ago
I'm having a lot of trouble finding an AC power supply (Almost everything I see is AC/DC). Even at Digikey their wall transformers only go down to 6Vac which seems like too much for my project, as I am looking for a 3Vac to 3.5Vac supply. Is there a specific term I need to be searching besides "AC Power Supply" or any suggestions on a website that I can find one at, I can't even seem to find what I need on Ebay.
sockmaster (author)  Malicah1 year ago
I can't find one below 6VAC on DigiKey either. You could try local surplus electronics stores. If you can't find one, there is an easy way to drop the voltage of an AC supply. Adding doubled-up diodes (one facing forward, one backward, soldered together) in series with one of the wires coming off the supply will drop the voltage by about 0.7 volts. Adding 3 or 4 sets of diodes should lower the voltage to a safe level.
Freestila2 years ago
Hi, i love this thing :) I'm building one myself, but i have some problems with the leds: Most of them are not completly flat and dont work well, you have t position them exactly rigth to light up. What i need is something under every led pole to make the surface flat and allow a good electric connection. But since i can't solder some Lead or so on (don't want to break the magnets), i don't have any idea what to do...

Someone got any idea? I thought about adding a second magnet to every pole, but on one side i don't have enough magnets left (and since i got them from hongkong it would take about one month to get new ones), and second i would fear that i get a short cuircit when the second magnets attract themselfes...
kalexander2 years ago
this is amazing! can you do this on a metal fridge?
You have to for the magnets to work. If you are wondering if the mettle on the fridge would mess it up that is what the white paint is for that he put on before the nickle paint.
leckywong4 years ago

-One 4.5 Volt, 500 milliamp AC power supply
By using AC, the polarity of the LEDs won't matter. They will light up whichever way they are played onto the grid. This also reduces power consumption because the LEDs will run at a 50% duty cycle.

I have a question: Can the LEDs work under AC power?
YES...BUT make sure that the voltage on the AC power is NO HIGHER then the reverse voltage on the LED.

LED's can be killed if the reverse voltage...ie the voltage that the LED see's if you connect it back to front to a DC supply...typically about 6v

To explain it another way, connect an LED to a variable supply, and turn the power up to 2 or 3 volts, what ever its 'forward max voltage is, it will light, turn up the DC to say six volts, its now dead!

take a similar LED and connect it the reverse way around, it wont light, its safe at 3 volts, 4 volts, 5 and maybe a bit higher...then it will DIE.

so if you feed a LED with AC, the AC has to be NO higher then the forward voltage of the LED

I hope i explained that?
yes, they will only be on half of the AC cycle time, but you cant see it
To further clarify. Yes you can use Alternating current if the voltage is correct. You will be able to see the LED. The Switch rate, for USA is 60hz or 60 times per second and Most other places is 50hz. Regardless, it will be Half the brightness as the DC current for that voltage.
groelofse3 years ago
This look great, love the idea and would like to have a go making it. I live in the UK and can't find the paint you have used, the only other thing that seems to be a possible conductive 'spray' option is zinc primer... anyone got any thoughts on if this would work the same....
No Zinc pint wont work, although Maplins do a paint on version of the conductive paint in tiny amounts,but its very expensive.

Or look here:-

http://www.ecosorganicpaints.co.uk/store/specialist-paints/anti-emr-wallpaint/cat_49.html
Thanks for link. I discovered RFI spray paint at RS Components, so problem solved :-)
But please look better groelofse
RS components are for commercial users and as a result you pay a very high price for the technical backup, please look elsewhere, look at the spec of the RS stuff, and even find out the manufacturer, then look at the manufacturers website, see if there is a stockist.

Another point to realise, is one product is silver based, and can carry current, another is graphite based and only carries voltage, as its resistive. This is the usual stuff you get with RFI based coatings..it WONT carry current very far to light LED's

If you look at MG chemicals, they supply to companies who ship to the UK, at rates better then RS
Any other help i can give, please ask.

John
is it possible to just get a copper plate (sheet metal) and hook up the current to that without having to paint it?
pyrotech454 years ago
my white board wont be plane anymore!
shahzade4 years ago
dude, this is so ingenious, i love it! well thought and well proceeded. your own idea?
shmolky4 years ago
The way you added the resistors was really very clever. Mad props.
Kryptonite4 years ago
Hey! That's so awesome, I love how each single LED is just so compact, and how it can just be popped onto the fridge and it lights up! Brilliant! 5/5*, faved and subbed.
depotdevoid4 years ago
Hi sockmaster, I don't know if you're still checking your instructables messages, but I thought I'd let you know, great project!  Here's a picture of the one I made:
Picture 5224.jpg
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