Intro: LED Backlight LEGO Boo! Night Light
Sleep tight!...but you might want to keep one eye half open if you're sleeping with this gang of ghosts and goblins.
This Instructable demonstrates how to use LEGO's to build a small frame for an LED Backlight. LED Backlights are great for making electronic name tags, nameplates, and night lights. Like a regular LED, the LED Backlight can be powered by CR2032 button batteries (child-safe method featured here), AAA-batteries, or you could even hack a LEGO LED accessory and use a LEGO battery pack. With a magnet attachment, the night light easily converts to a lighted name tag for Halloween night. Boo!
White LED Backlight - Medium Size (Adafruit.com)
Stick-On Adhesive Letters "Boo!" (Walmart)
LEGO Bricks and Figures
Black Plastic Battery Holder for 2 x 3V CR2032 Coin Button Cell
One CR2032 button battery
Magnetic Name Tag Holder with Adhesive on Front Plate (Amazon.com)
2 Lincoln Head Pennies
Step 1: Step 1: Obtain and Test the LED Backlight
The LED Backlights are available in White from Adafruit.com for about $2.50 each. This LEGO project features the medium size white Backlight which is approximately 1-inch wide and 3-inches long.
The backlights utilize HDTV-type technology to evenly spread out the light from a single LED. As such these LED's can be tested as simple "LED throwies" with a 3-volt CR2032 button battery, as shown. During your testing, be sure to note which side of the backlight is lighted and which side is dark. You can make a note with a Sharpie marker to say "back" on the back or dark side.
Surprisingly, a single CR2032 battery can keep the white LED lighted for almost 2 weeks, although it will dim with time. For further background on LED throwies, be sure to see the classic LED Throwie Instructable.
The green backlight above is special order, but illustrates that brilliant colors are possible by changing the color of the LED light source. Until such colorful backlights are available on the market, gel color sheets can be used to add color to Adafruit's white backlights. Also note that Sharpie or Erasable markers can easily be used to make your "Boo!" lettering, although I have been mostly using stick-on letters.
Step 2: Prepare a Child-Safe Battery Holder
The lithium CR2032 button batteries present a child safety hazard (swallowing). Safe use around small children requires a battery holder that can be closed and screwed shut. Adult supervision is then required for battery replacement.
The black 2 x CR2032 button battery holder shown above is available from Amazon.com as well as Adafruit.com. If you have two of these, you can scavenge the two small set screws from one unit, and use it to secure the battery compartment with four screws as shown.
There is a small ON/OFF switch on the battery holder. Turn it OFF for now.
IMPORTANT: This project features the use of one, single 3-volt CR2032 battery. Therefore it is necessary to put a "fake" or "dummy" CR2032 battery in one side of the 2xCR2032 battery holder. As shown above, two (2) Lincoln pennies are used to fill the open extra space.
DO NOT use two CR2032 batteries unless a resistor is added to the LED circuit (discussed later). With two batteries, the battery holder provides 6-volts which can burn out the LED.
Test the final assembly to make sure the batteries cannot be accessed except by an adult. If the tiny screws are not holding tightly, consider electric taping the battery holder shut.
Step 3: Build the LEGO Structure
The basic idea is that a 5x12 LEGO box provides a nominal 1x3 inch hole that perfectly holds the LED backlight, as well as several different types of battery holders for power.
With reference to the above photos, start with a flat 5x12 black LEGO base, which actually consists of two 2x12 and one 1x12 piece in the center.
On top of the black base, place your orange box. The cut-away view shows the height of the box for this project is 4 LEGO units tall. Next you will need to insert four LEGO pegs, which as shown in the cut-away view, is used to elevate the backlight to the exact top surface of the orange box. The pegs are about 2.5 LEGO units tall, by use of the red end caps.
Next, to finish out the functional part of the box, two 2x4 orange base pieces are used on the ends to hold the backlight into place.
Finally, round up the likely suspects (ghosts and goblins), and let your own artistic talent (and available LEGO pieces) guide you to finish the project. This project was built from random pieces we had, so I cannot advise a specific LEGO set. See later examples made from a specific LEGO set. Note the orange box for the LED can optionally be made taller, to provide a deeper box as needed for options such as a 2xAAA battery holder and so on.
Step 4: Assemble the LED and Battery Holder
In order to fit easily into the LEGO box, it is imperative that the LED Backlight's wire leads are bent back sharply to the back, as shown. Using wire cutters, shorten the LED wire leads in preparation for soldering. Also using wire cutters, shorten the battery holder wire leads, but leave a loop or slack for stress relief. Solder the battery holder wire leads onto the LED wire leads as shown. Preferably the back side of the battery holder (with the screws) faces the back side of the backlight , as shown. Although its always important to maintain proper +/- polarity in your wiring, if you get it wrong, you can simply put the CR2032 battery into the battery holder backwards. Now turn the battery holder switch to the "ON" position and check for proper LED light operation.
Once assembled, the "Boo!" lettering can be carefully applied, using a straight edge for guidance. Be sure to center the lettering, and keep it within the lighted window boundaries of the box (you don't want the lettering to get covered by the LEGO end pieces).
Finally place the LED/battery assembly into the orange box, such the LED backlight rests firmly and level on the support pegs. A toothpick may aid in lining up the battery holder, and can also be used (as shown) to access the ON/OFF switch.
NOTE: Adafruit.com is now offering this battery holder with a JST end connector. This may allow a no-solder assembly option. The simple way I use the JST end connectors, I usually just stick the bare LED wire leads right into the JST sockets.
Step 5: Use Stick-On Magnet to Convert to Name Tag
If you've ever been to a LEGO or Brick show, you know the display persons hang relatively large LEGO structures on their shirt pockets. This is accomplished by name tag magnets that are readily available, for example, from Amazon.com.
The Boo! LEGO night light is easy to wear as a name tag, but obviously the ghosts and goblin characters will tend to get bumped off. You might consider removing the characters, or gluing them on with SuperGlue.
Step 6: Other LEGO Backlight Structures/Comments
Those with LEGO skills will recognize many other LEGO structures are possible, all featuring the same basic 1x3-inch box frame to house the LED backlight. If you are new to LEGOs, a useful LEGO kit to start with is the LEGO® Classic Medium Creative Brick Box 10696. That kit should allow making the structures shown above.
As shown, a 2xAAA battery holder also fits into a little deeper version of the basic LEGO box structure (perhaps with a little sanding on the sides of the plastic battery holder to make it fit).
For 2xAAA batteries (which have less internal resistance than the CR2032 button battery) an approximate 50 ohm resistor is required. Because the 2xAAA battery holder does not have a power switch, you can opt for Always-ON operation (should last for weeks) or you can add a power switch (see Noah structure above). The LEGO plastic is easy to work with, and you can drill neat holes by just spinning a small sharp drill bit with your bare fingers.
Another power option is to use the a regular LEGO battery pack and a LEGO LED light accessory. Simply cut off the LEGO-supplied LED and solder the wires onto the LED backlight leads.
For those wishing to power the project with the 2xCR2032 battery holder of this project, but with two CR2032 batteries, you will need an approximate 200-400 ohm resistor to moderate the resulting 6 volt output.