Introduction: Awesome LED Edge-lit Desktop Nameplate
The concept of this project is simple; engrave a name on a piece of clear plastic sheet then shine a light on the edge of the plastic. The letters and edges are vividly illuminated whilst the clear material remains completely transparent.
To add a touch of color, use multicolored RGB LED's in conjunction with a microcontroller. This combination allows hundreds of different colors to be achieved. With just the touch of a button, transform the work piece from red, to green, to blue and anything in between.
This Instructable requires basic knowledge of wood working, hand tools, electronics, programming, and soldering.
Step 1: Gather Materials
Materials:
1 - Polycarbonate Sheet - 10.75in x 2in x 0.25in - local plastic supplier, $3
1 - Oak Board 24in x 5.5in x 0.25in - menards, $3.31
1 - Wood Glue, 4 fl. oz - menards, $3.88
16 - RGB LED's w/diffused lenses - sparkfun.com, $1.99ea
32 - 100 Ohm, 1/4W, 5%, Resistors - jameco.com, $0.02ea
16 - 180 Ohm, 1/4W, 5%, Resistors - jameco.com, $0.02ea
1 - 1K Ohm, 1/4W, 5%, Resistor - jameco.com, $0.02ea
1 - 560 Ohm, 1/4W, 5%, Resistor - jameco.com, $0.02ea
1 - 0.47uF Monolithic Capacitor - jameco.com, $0.12ea
1 - PICAXE 8 Pin Microcontroller - sparkfun.com, $2.95
1 - PICAXE 8 Pin Proto Kit - sparkfun.com, $3.95
1 - PICAXE USB Programming Cable - sparkfun.com, $25.95
1 - Darlington Driver 8-Channel ULN2803 DIP - sparkfun.com, $1.95
1 - 18 Pin DIP socket, - sparkfun.com, $1.50
1 - Mini Push Button Switch - sparkfun.com, $0.35
1 - 2.1mm DC Power Jack, Male - jameco.com, $1.49
1 - Break Away Header - Straight -sparkfun.com, $1.50
1 - Rocker Switch, DPST, ON-OFF, Black - jameco.com, $1.49
1 - Break Away Header - Right Angle - sparkfun.com, $1.95
1 - Wall Adapter Power Supply, 5VDC 1A - sparkfun.com, $5.95
4 - Multipurpose PC Board with 417 Holes - Radioshack, $1.99ea
22AWG Solid Jumper Wire, Various Colors - jameco.com, $6.95/100ft
5 - Hex Socket Cap Screws, 4-40 x 1/4in - mcmaster.com, $7.50 (100)
Tools:
Wire Stripper
Side Cutter
Needle Nose Pliers
Dremel High-speed Rotary Tool
Dremel Engraving Bit
Needle File Set
Sandpaper (600/800 grit)
Utility Knife
Mini Vise
Digital Multimeter
Third Hand Tool
Soldering Iron/Station
Solder
Drill
3/32 Drill Bit
3/32 Hex Driver
Vernier Calipers
Metal Ruler
Small Bar Clamps
Saw
Computer
Safety Glasses
Step 2: Design Graphics
The number of characters in chosen name will define all of the other parameters of the nameplate, so it is important to design this element first.
1) Layout characters. Use a text editor or CAD software so that changes in font and size can be realized immediately. Note: Any font or handwriting style can be used. I designed my own font in CAD software, where each character was approximately 0.7in wide and 1.13in tall with 0.05in of spacing between each character.
2) Measure the total height and width. Record the maximum height and maximum total width of the string of characters you have laid out.
3) Calculate size of polycarbonate sheet. Allow for a small border around the text. On the top and both sides of the text an approximately 0.25in-0.5in border is usually appropriate. The bottom border should be a bit larger to allow the light from the LED to spread out. A border of 0.5in-0.75in would be appropriate. Add the border dimensions to the text dimensions in the previous step.
Step 3: Engrave Polycarbonate
1) Cut polycarbonate sheet. Size specified in the previous step. In my case this is 2in. x 10.75in.
2) Transfer the outline of the graphics. This can also be done in a couple different ways. The first, place the graphic under the clear sheet and look through it free handing the graphic onto the sheet. The second, use Grafix Rub-onz sheets (hobby Lobby or Dick Blick) to transfer the image to the top of the polycarbonate.
3) Engrave graphics. Use dremel to grind away material inside of the text you have created. Remember the area where material is removed or scuffed will shine in the light of the LED’s. Try not to mill a slot with a rectangular cross-section into the sheet. A groove with a semi-circular or triangular cross section will transmit the most light.
4) Clean edges. Remove any burs or melted polycarbonate from the sheet.
The second and slightly fancier way of engraving it is to use a CNC machine. A CNC machine is the fastest most accurate way to engrave, but requires CNC knowledge, can have high cost and can have limited availability.
I chose to have the name plate machine engraved. Since, I have the knowledge and machine availability this was the fastest and highest quality option to choose.
Step 4: Polish Polycarbonate Edges
Polishing the edges serves a dual purpose. Polishing the top and side edges is aesthetically pleasing and on the other hand polishing the bottom edge will allow more light to be transmitted by the LED’s.
1) Sand edges. Use progressively finer grit sandpaper starting at 220 ending at around 600. For best results finish with 800 grit sandpaper. Be careful to not scuff the front or back sides of the sheet with the sandpaper and try to maintain an edge that is perpendicular to the front and back sides.
2) Clean edges. Gently wipe with wet towel and dry.
3) Heat edges until clear. Use a concentrated heat source to heat the edges of the polycarbonate to a high gloss finish. Heat sources can be heat guns, lighters, or mini blow torches. You can over do this! Take your time working slowly along the edge close enough to barely melt the sheet.
Step 5: Design LED Circuit
The LED circuit consists of three microcontroller switched loops: one for red, one for green, one for blue. Each LED has four different leads: red, green, blue, and ground. Each of the color leads is connected to its respective loop via a current limiting resistor in parallel with the other leads of the same color type. The ground leads are all connected together.
1) Determine how many LED’s will be required. The high brightness RGB LED’s must be spaced approximately 0.5in-0.75in apart on center. Divide the total length of polycarbonate by a number in the range given (10.75 / 0.7 = 15.36). In this case use 16 LED’s.
2) Determine supply voltage, Vs. 5VDC is a good number because the microcontroller can run of 5VDC without requiring a voltage converter.
3) Determine required resistor values. Check the LED’s datasheet for the FORWARD VOLTAGE, Vf and the MAX FORWARD CURRENT, If. The resistor value is determined by the following equation: R = (Vs – Vf) / If
Red -> Vf=2.0V @ If=20mA => R=150Ohm
Green -> Vf=3.2V @ If=20mA => R=90Ohm
Blue -> Vf=3.2V@ If=20mA => R=90Ohm
Note: The resistance calculated is the resistance required to hold the LED at 20mA of forward current. Remember that exceeding the max rated current will significantly decrease the life of the LED. Also, remember that common resistors have a tolerance of 5%. To avoid accidentally exceeding the rated max current, select a common valued resistor value greater than 5% of the calculated minimum resistance. I chose a 100Ohm resistor in place of the 90Ohm resistor and a 180Ohm resistor in place of the 150Ohm resistor.
4) Determine resistor power rating. Resistors have a MAXIMUM ALLOWABLE POWER, Pmax rating. If you exceed this rating the resistor will incur permanent damage and inevitably fail. The maximum power dissipated each resistor is as follows: Pmax = R x If^2
100Ohm @ 20mA => P=40mW
180Ohm @ 20mA => P=72mW
These are both under 1/4W so 1/4W resistors will be adequate.
5) Determine total power dissipated in each loop and total current in the circuit. The sum of the total power will determine the current rating needed for the power supply. Furthermore, the microcontroller can only source 20mA of current per pin; so, a Darlington Driver IC is used to allow the microcontroller outputs to control high current loads. This IC has a max current rating of 500mA per channel. Pmax = #LED’s x [( Vf x If) + (R x If^2)]
P(red) = 16 x [(2V)(20mA) + (180Ohm)(20mA)^2] = 1.792W <------- Pmax
P(green) = 16 x [(3.2V)(20mA) + (100Ohm)(20mA)^2] = 1.664W
P(blue) = 16 x [(3.2V)(20mA) + (100Ohm)(20mA)^2] = 1.664W
Max Current = Pmax/Vs = 1.792W / 5V = 358.4mA
Total Current = [P(red) + P(green) + P(blue)] / 5V = 1.024A
The Max Current in any loop is less than the max rating of the Darlington Driver so it can be used. The Total Current is very close to 1A. Sparkfun’s 5VDC 1A Wall Adapter Power Supply is rated for well over 1A so it will be suitable.
Step 6: Assemble LED Circuit
1) Cut Radioshack circuit board in half. The Radioshack circuit board is not symmetric, so both sides cannot be used in the same project. The half to be used is 8holes x 25holes (shown in pictures below). To cut the board in half, score both sides of the the board with the utility knife along the terminal strip that runs length wise on the side of the board that is to be discarded. Use the edge of a table to break the board along the scored line. Then, use a Dremel high-speed rotary tool to grind the edge flush to the remaining lengthwise terminal strip.
2) Trim sides of board. In order to maintain an even distance between the LED’s the short sides of the board need to be trimmed. With a utility knife, score both sides of the board along a line parallel to the edge that intersects the center of the mounting hole. Use two pliers to break off the unwanted edge.
3) Solder resistors in place. Bend the Leads so that they will fit between the locations shown in the CAD model pictured below. Place the resisters in their respective positions as indicated, solder in place, and trim the leads.
4) Solder jumper wires in place. Cut to length and strip the insulation from the ends of the 22AWG solid copper wire. Solder in place bridging specified nodes. Trim extended leads.
5) Solder LED’s in place. Place LED’s in correct position observing the correct polarity of the diode. The names of the leads are indicated in a picture below. Solder in place maintaining the vertical axis of the LED perpendicular to the top of the circuit board. Trim extended leads.
6) Join Subassemblies. Cut to length and strip the insulation from the ends of the 22AWG solid copper wire. Solder in place bridging specified nodes. Trim extended leads.
Step 7: Assemble Microcontroller Circuit
The microcontroller circuit is very simple. The basis of the circuit is the PICAXE 8 Pin Proto Kit. Three output pins pass through a Darlington Driver to the three LED loops and one input pin senses the state of a push button switch. The entire circuit is built directly on the proto kit’s development area. Please note this microcontroller circuit is appropriate for any situation in which each LED loop consumes less than 500mA.
1) Solder kit components in place per kit instructions.
2) Solder 18 pin socket in place. Remove the four of the pins closest to the notch in the short side of the socket. Solder socket in the offset location indicated in the picture below.
3) Solder in place mini push button switch and debounce components. To solve the problem of switch bounce, I have included a hardware debounce element consisting of a 560Ohm resistor and a 0.47uf capacitor. Reference the schematic and the pictures below for correct placement. Trim leads.
4) Solder jumper wires between components, microcontroller pins, and supply rails. Reference the schematic and the pictures below for correct placement. Trim leads.
5) Solder headers in place. Place the 2x1 90degree header and the 5x1 straight header in locations specified below.
Step 8: Design Base
Step 9: Assemble Base
Assembly of the base is quite simple given the drawings generated in the previous step.
1) Cut all components.
1) Glue sides to top.
2) Glue Ribs in place.
Step 10: Assemble Nameplate
Final Assembly is composed of connecting all of the individual components produced in the previous steps.
1) Solder jumper wires between proto board supply header, on/off switch, and supply jack.
2) Solder jumper wires between proto board and LED circuit assembly.
3) Screw proto board in place.
4) Screw LED circuit assembly in place.