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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

Picture of 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.

Step 2: Paint The Fridge

Picture of Paint The Fridge
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Wash the surface of the fridge first. Once dry, use masking tape to mark off the borders of the grid (display area) and the power traces going to it. Get some newspaper and with more masking tape, cover up all the areas you do not want to get paint on.

Apply one even coat of the base paint. I used this base coat to cover any existing scratches on the surface of the fridge and also to help ensure that the conductive paint will not peel off.

Once the base coat is touch dry start applying the 1/4" masking tape (Quilter's tape) to form two seperate traces that will power the grid, and then apply all the traces in the grid itself. I used a marker to mark out the vertical spacing between the horizontal lines, then followed the dots as I placed the tape by hand.

The grid should basically look like two interlocked combs. One power line will go to the left side and make "teeth" going back to the right, and the other power line will start at the right side, making teeth go to the left. Neither of the two power lines should ever touch at any point. The grid is basically an open circuit and closed only when the magnetic LEDs will be placed upon it - one magnet of the LED touching one power line and the other magnet touching the other.

As soon as the masking tape is applied, start painting with the conductive paint. This stuff is nasty - you want to make sure that the area is well ventilated. Open all windows, doors and turn on the vent over the stove.

Keep applying more layers until the can is nearly empty. You may want to save a little bit just in case you ever need to touch up the conductive traces. If you are painting a larger surface area, you may consider using more than one can.

Step 3: Remove The Masking Tape

Picture of Remove The Masking Tape
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Once the paint is touch dry, start removing the newspapers and masking tape, starting from the outside and working your way inside to the finer traces.

Be very careful pulling up the masking tape because the conductive paint is so thick that it may pull off along with the tape. I used an X-acto knife to score the edges in the corners of the fine traces to prevent the paint from being lifted off. Should any conductive traces start lifting, you may be able to press them back down if the paint is still not completely dry. After it is dry, you may try using Crazy glue to glue down any lifted corners.

Step 4: Hook Up The Power

Picture of Hook Up The Power
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I used a 4.5 Volt / 500 milliAmp AC power adapter with magnets attached to both wires to power the grid. The wires are glued to the magnets and the tops (not bottoms) of the magnets are covered in hot glue to prevent the two magnets from shorting the circuit should they touch each other. The magnets can be oriented so that the bottoms are magnetically opposed - which should prevent them from attaching to each other if they get pulled from the fridge.

There is a gap in the circuit between the door and the side panel of the fridge. To complete the circuit, I used two small jumper wires with magnets attached to both ends. Make sure to leave enough slack in the wires to cover the gap even when the fridge door is opened all the way.

Now the grid has power. Since the LEDs are not constructed yet, you may test the circuit simply by placing some magnets onto the traces of the grid and lying some LEDs over the magnets. The pins/wires on LEDs are attracted to the magnets, so no special effort is required for this test.

I measure 15 Ohms of resistance on each trace going from the back of the fridge to the grid, and about another 15 Ohms from the side of the grid to the center. When I place a jumper wire in the center of the grid, I measure about 60 Ohms between both power terminals at the back of the fridge - so a full circuit between the power supply, crossing any given point of the grid and back to the power supply is about 60 Ohms.

I found that the conductivity of the paint increased as the paint dried, so don't be too worried if you're getting readings higher than that at first. If you get something much higher or much lower, you may opt to use a different voltage power supply to compensate or use copper tape to reduce resistance in the traces.

Step 5: Assemble The 3.6 Volt LEDs (blue, white and green)

Picture of Assemble The 3.6 Volt LEDs (blue, white and green)
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Bend the pins on the LEDs to lie flat, then use the wire wrapping tool (or similarly tipped tool) as a shape to bend the wires around so that they encircle the tool. Try to make it so the outside of the circle shapes reaches the outside edges of the bottom of the LED and that both circles are on opposite sides of the LED.

Once the wires are bent, use nail clippers or small wire cutters to cut off excess wire. You only need one looping of the wire to form a circle with each LED pin. Next, use needle-nose pliers to adjust the loop so that the inside of the circle is just a little bit smaller than the diameter of the magnets. This will add a bit of spring to the wires so that they clamp over the magnets when you push them in. (Don't add the magnets just yet.)

Before attaching the magnets to the LEDs I used modeling clay to hold the LEDs upside-down. Get your magnets ready. Mix up a small batch of epoxy. Apply a small bit of epoxy into the center of each circle of wire. Apply just enough for the magnets to hold without having the epoxy overflow over the bottom of the LED.

Now place magnets onto one side of each LED. They will most likely just jump onto the top edge of the circle of wire as the wires will attract the magnets. Once one row is place, use the cap from a cheap pen to push the magnets into the center of the circle and press down on them until they "click" into place. If they don't "click", or are too hard to push into the circle, you may need to adjust the diameter of the looped wire on your next batch of LEDs.

Add magnets to the second row of pins in the same way. If any epoxy gets onto the pen cap, just wipe it clean with a tissue. This will prevent covering the tops of the magnets with epoxy.

For the next minute or two, use the pen cap to level off the tops of the magnets. Then let them sit for 20 minutes or so. You do not want to be moving the magnets now because it will potentially break it's contact with the looped wire.

After 20 minutes, you can use a toothpick to carefully scrape any epoxy that may have covered the top surface of the magnets. Don't try placing the magnets onto your fridge until several hours have passed as the metal surface of the fridge will pull at the magnets and break the contact with the LED wires.

You can test your LEDs before the epoxy has completely hardened with a 3V battery attached to small wires - simply touch the wires to the magnets to see the LEDs light up. Try both ways because LEDs will only light up if power is hooked up in the correct polarity.

Step 6: Assemble Magnets To The 2.4 Volt LEDs (red and yellow)

Picture of Assemble Magnets To The 2.4 Volt LEDs (red and yellow)
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The 2.4 Volt LEDs start similar to the 3.6 Volt LEDs, but the wires are bent in a different way to allow for a resistor to be added to the bottom of the LED.

Bend the longer wire of the LED to lie flat and point straight out. Next bend the shorter wire to lie flat around 40 degrees below the first wire. Bend the first wire to come back towards the LED. Make the bend overhang the edge of the LED a bit to make it easier to cut later. Next, use the wire wrapping tool to curl the bent back wire into a circle. Do the same with the next wire. Try to keep the loops evenly apart, with the edges of the circles going right up to the edges of the LED.

Use nail clippers or a wire cutter to cut off excess wire. You only need the wire to make one loop around. Use needle-nose pliers to tighten the inside diameter of the circles to be just slightly smaller than the diameter of the magnets so that the wires will clamp around the magnets when they are pushed into place later.

Place the LEDs in the modeling clay and use epoxy to attach the magnets just like with the 3.6 Volt LEDs.

When it comes to testing the LEDs to check that they light up, add an extra resistor to the battery because 2.4 Volt LEDs will burn out without a current limiting resistor.

Let the epoxy harden for about two hours, but do not place these LEDs onto your fridge because without the resistor (next step), they will burn out.

Step 7: Add Resistors To The 2.4 Volt LEDs (red and yellow)

Picture of Add Resistors To The 2.4 Volt LEDs (red and yellow)
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Once the epoxy on the 2.4 Volt LEDs has hardened, use nail clippers or small wire cutters to cut the overhanging wire loop off the LEDs. Be careful not to add too much stress to the wires as this might pull off the newly epoxied wire loop and magnet. If this happens you can use Crazy Glue to reattach it.

Cut and bend the wires to make room for a surface mount resistor. The resistor should rest about halfway between the edge of the magnets and the edge of the LED itself. Use an X-acto blade or toothpick to bend the wires down a bit so that they will clamp down on the resistor once it is wedged underneath them.

Attach a small piece of double sided tape to the end of your blade. This will make it easy to pick up and position the tiny resistors.

Now it's time to solder in the resistors. This takes a delicate touch. Make sure to clean the soldering gun's tip often and lightly touch the points you want to solder with both solder and pre-heated soldering gun. If the solder doesn't "take" the first time, wait until the wires cool and try again. Make sure not to touch the magnets with the soldering gun. The magnets will break down if exposed to excessive heat. If you accidentally solder a bridge over both wires, use the toothpick to push apart the solder as you reheat it.

For those who are unsure of their soldering ability, it might be possible to omit the soldering step altogether if you make sure the wires firmly clamp down on the resistors. Test the LEDs to make sure they're working and then put a dab of epoxy over the resistor to keep it from moving out of it's current (working) position.

Repeat steps 5, 6 and 7 until all the LEDs are assembled.

Step 8: The Finished Project

Gather all the LEDs and place them on the fridge. Now it's time to start making pictures on your fridge.

When not used in the grid, the magnetic LEDs can also be used as regular refrigerator magnets - although they won't light up unless they're placed in the grid.
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shadus8 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 shadus8 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 shadus7 years ago
let me guess a past "Learning experience"??? lol!
Malicah2 years 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)  Malicah2 years 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.
Freestila3 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...
kalexander3 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.
leckywong5 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.
groelofse4 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?
pyrotech455 years ago
my white board wont be plane anymore!
shahzade5 years ago
dude, this is so ingenious, i love it! well thought and well proceeded. your own idea?
shmolky5 years ago
The way you added the resistors was really very clever. Mad props.
Kryptonite5 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.
depotdevoid5 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:
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