Intro: USB Powered LED Tracing Light Box
Build a portable USB powered Light Box to help trace pictures from books or assist with your craft activities.
Whats different about this Light Box is that it is super slim so it can be slipped behind the page of a book easily and is powered off a USB port so is conveniently portable and compact.
Great gift for art students or anyone who enjoys craft activities.
Step 1: Gather Materials
Step 2: Dissassemble the Whiteboard
The objective of this step is to salvage the plastic surround from the white board with the least amount of damage.
Note: Ensure you were leather garden gloves when dismantling as magnetic white boards contain sheet metal which is very sharp and you can easily cut your hands when pulling it apart.
Use a craft knife and a flat head screw driver to pry apart the plastic surround and gently cut through any hot glue holding it together.
Discard the white board interior however it is useful to keep the internal cardboard as it can be used as a template for cutting the perspex. (alas... unfortunately the duck was not required either!)
Step 3: Build the LED Back Light
The LED back light is made up of a series of strip LEDs that have been individually positioned on cardboard backing in an 15x11 grid and soldered in parallel to each other.
Use cardboard that is at least 2mm thick as the backing and cut to the same dimensions as the template produced earlier.
Using a ruler and pencil mark out where the LEDs should be in an 15 x 11 grid to maximize coverage of the area.
2. Position the LEDs
To keep costs low I used strip LEDs that come in a large reel and are connected for a 12v power supply. These are actually just 3x3v LEDs in series.You will require 161 LEDs so cut them into individual squares being careful not to damage them and discard the leftover offcuts.
Peel off the tape backing and press into position being careful to orient each of the LEDs so that the Cathode and Anode are aligned vertically in rows as per the photo.
Retain the 150 Ohm resister on one LED per row so this can be used to limit current and overheating of the LEDs. See photo above. This enables you to power the 3v LEDs in each row from the 5v USB power supply with out them overheating or being damaged.
3. Soldering and testing the LEDs
Connect each of the LEDs in a column using hookup wire and solder them together. Note the top and bottom wires extend to the edge of the cardboard so they can be connected together.
Use the enclosed photo to ensure you have the LEDs connected correctly.
It is worth while testing the LEDs in each column as you proceed to avoid any nasty surprises of reversed polarity. You can do this by attaching a 1km resistor to a 9v batter and using two wires to test each column in term before they are connected up.
A 150 Ohm resister on one LED per row is used to limit current and overheating of the LEDs. See photo above. This enables you to power the 3v LEDs in each row from the 5v USB power supply with out them overheating or being damaged.
Top and bottom the Anode and Cathodes are all connected in parallel and at completion are connected to two insulated wires that will attach to the USB socket
Step 4: Building the Front Panel
1. Planning the size of the front panels
The front panel has three layers that sit over the top of a LED Light Board.
Build or re-use the interior cardboard cutout from the Whiteboard as a template to determine the exact size of the layers required. This can be used as a template in the next few steps.
2. The first Layer - Perspex
This step is harder than it sounds and therefore I recommend that you practice on some offcuts before trying with your final piece.
Mark out the Perspex with the correct dimensions from step 1 above and use a a Jig Saw with a fine blade to cut the correct size perspex.
In my case I had to drill 8 holes to allow the plastic trim on the corners of the whiteboard to fit together correctly. If you have to drill holes I recommend starting with a small drill and increasing the hole one size at a time until you get the correct size. Perspex is very brittle and will crack very easily so take care and take your time.
3. The 2nd Layer
Take a Clear Black Plastic Sheet ( from an "L-shaped" document holder) and place an A4 white sheet of paper in this. Mark out the correct dimensions from step 1 above and using scissors cut to size.
4. The 3rd Layer
This layer is constructed from an Opaque piece of plastic sheet that is 2 - 3mm thick. I went to a $2 store and purchased a thin white plastic kitchen chopping board for $2 and this was ideal.
Mark out the correct dimensions from step 1 above and using the jig saw or a junior hack saw again cut to size.
5. Testing the unit
At this point it is worth while testing the unit so connect the wires up to a 5v power supply to check that the LEDs are working correctly. I used a USB cable that I cut the end off and and a breadboard to do this however you can use other power supplies.
NOTE: I recommend you place a 10ohm resister in series with the LEDs as some "Cool white" LEDs get warm. Ensure you do not exceed 5v and be careful of the polarity otherwise the LEDs will be damaged when testing.
Step 5: Install USB Power Socket
1. Prepare the Vero Board
The USB socket needs to be mounted so it is very firm to ensure that pushing in and removing the USB power cable will not affect the connections.
Therefore a piece of Vero board is used to mount the USB socket and fix into place.
Place the Vero board over the area and trace around it before cutting, drilling and filing to get the correct size.
2. LED Board connection to USB
A small cutout is made in the case with a craft knife to enable the USB socket is accessible from the outside of the unit. Position the USB socket on the Veroboard and mark the case before cutting.
The USB socket is mounted on the piece of Vero board and as well as soldered is glued with two-part epoxy to ensure that it is firmly attached.
The positive or Anode connection to the LEDs needs to be connected to pin 1 of the USB Socket. The negative or Cathode needs to be connected to pin 5 of the Socket.
Note: Please ensure this is correct otherwise it could damage the LEDs. Use a multimeter to test the wiring before connecting to a USB port to ensure polarity is correct.
Once tested the Vero board is glued into the chassis with Hot Glue gun to ensure that socket is rigid.
Step 6: Final Assembly
Ensure that the lights and each layer are correctly positioned and that there is not dust or particles trapped under each layer.
Test the unit to see if there are any issues before finally attaching all of the required plastic fittings and glue in pace with a Hot Glue gun.
I also added some soft rubber feet on the bottom of the unit so it sat nicely on hard surfaces however this is not mandatory.
You can use this with PC USB adapters and Mobile phone chargers as long as they have the standard USB plug in them.