Introduction: Miniature RGB LED Sign Assembly (Solid Color)

By boraini.com

In this Instructable I'd like to tell how I builded this LED sign for use at various events. I love projects that light up, and I have a recent interest in making light-up signs for the conventions and fairs where we have a stand to demonstrate something, for example a fair where we present our startup. I have built similar signs before. I built my first one in one night using a taped together frame made of balsa wood roughly cut with a box cutter. It lit up with white LED strips and I could hang photocopies/cut-outs in front of it to achieve various designs. It got destroyed after using at a student council event and a startup fair; I expected looking at my horrible artisanship. (I have no photos of it now)

I wanted to do better for next time, so I started building another one. This time I worked with a fabricated LED sign box (but it isn't cheating because the sign had any of its electronics including LED strips removed.) I used generic, solid color RGB LED strips to make the sign more all-purpose and to make it more fun to use. I plan to hang it in my room as decoration when I don't have an event to use it at.

Supplies

My materials list will be quite generic. You can build the frame using whatever material you can find, or replace any electronic parts if you know what you're doing.

Tools:

  • soldering iron
  • box cutter
  • pliers
  • tweezers

For the frame:

  • translucent white acrylic box (don''t get it so big that you don't/can't have enough LED strip)
  • plexiglass (I took a piece from an unused part of the acrylic box)
  • tin/aluminum foil
  • packaging styrofoam

Required Electronics

  • 12V LED strip power supply
  • perfboard (I could fit my circuit on a 10x16 hole single sided FR2 board)
  • ~1m of double wire power cable (connects between power supply and driver circuit)
  • some low gauge wire (should fit through the holes of the perf board, find solid core wire if you can)
  • straight male header pins (better buy 40-pin break-off ones)
  • Arduino Uno/Nano (any 5V microcontroller should work)
  • 3 x 220Ω 1/4W resistors (1/4W are the common, peach-colored resistors.)
  • 3 x IRF3205 N-type MOSFETs (P-type requires circuit modifications which I won't show. Any brand should work.)
  • Heat sink (optional)
  • Insulating PVC tape (I needed it to insulate the heat sinks of TO-93 packages (transistors,7805) from each other).
  • Solder wire and optionally solder paste

Optional Electronics for The 5V Power Output for Microcontrollers

(Skip these if you are only goint to use the sign with the microcontroller plugged in USB.)

  • L7805 5V voltage regulator
  • 2 x 100µF capacitors (rated 16V and above)
  • 5mm LED
  • 1 x 220Ω resistor (so 4 resistors in total) (I used a 10k resistor to further dim the LED. Another 220Ω should be cheaper for people buying everything.)

Step 1: Build the Frame

We will make an illuminated cover for the acrylic cover. In my case, I cut a sheet of thick styrofoam which covered the box, staying on its edges. I layered a sheet of aluminum foil on it to reflect anl light towards the cover back to the acrylic box. I layered the plexiglass on the top to make a good surface to stick the LED strips on. Finally I taped everything together.

I cut my LED strip into five pieces and stuck them on the plexiglass.(have as few pieces as possible, but also make sure to have an even LED distribution). My strip had a cable presoldered on it, to plug into a commercial strip driver, and I kept it on the first piece to plug into my own driver circuit. Finally I placed the cover on the acrylic cover and saw it worked with the LED cable sticking out.

Step 2: Build the Driver Circuit

The driver circuit should be simple to assemble for someone with some soldering experience. If the image showing my soldering work scares you please begin with other, simpler projects and gain experience. Also I won't give further instructions about assembly since I don't like my work either, but the circuit works fine.

The only advice I can give is:

  • Don't try to shrink your circuit if it isn't necessary. It is much easier for short circuits to occur in smaller handmade circuits. I burned an Arduino due to this.
  • Use newest components you can find. Components with previously bent legs/pins can break easily.
  • Make sure you use just enough solder. Again, we don't want solder blobs inducing short circuits or solder-deficient components moving around.
  • Be quick while soldering the LED, the MOSFETs and the 7805. Semiconductors get damaged by heat easily. Refer to datasheets if you want to pre-assess your soldering skill for this.

About the 5V regulator circuit: If you aren't going to power your microcontroller from the driver circuit but power it through its USB port, you can omit the entire circuit above the ground line in the schematic (marked with a red box.) I was going to power my Arduino through its 5V port of the driver circuit, but gave up after burning an Arduino due to 12V f r o m a s h o r t c i r c u i t.

Step 3: Putting It Together

Solder wires to the lED strip and connect it to your driver circuit's LED strip header pins. Connect control header pins to three analog output pins of your microcontroller using jumper wires. Connect the power cable of the driver circuit to the power supply's DC output. At this point the LED on the optional 5V output circuit should come on when you plug the power supply in mains. If no smoke is coming out, try touching the control header pins with your finger and LEDs should flash randomly.

Connect your microcontroller's ground pin to the 5V header ground using a jumper wire (don't connect driver 5V pin to anything yet). Connect the control header pins to different analog output pins on your microcontroller (I used pins ~9, ~10, ~11 on my Arduino Nano). Make sure the driver's 5V pin is still unplugged! Now you should be able to plug in the microcontroller in your computer's USB while also the power supply is on.

I attached some code for Arduino IDE+Arduino Uno/Nano which will fade the LEDs through raindow colors, which I used during the tests. (You can change the #define lines according to your wiring.)

Attachments

Step 4: Thanks for Reading

I know this isn't the best Instructable out there, but I think it is a good reference for someone who would like to attempt to a project like this. I will be improving the I'ble in the next week; let this be only a draft.

ıf you have any specific questions I'll be always here to answer. :)