Category Archives: Electronics

RGB LED Sun with Rainbowduino

So my current project (outside of massive amounts of school work) is building a large, bright, RGB LED display for my college’s weekend-long end-of-year party. I’ve got three of these strips from DealExtreme, which have 30 RGB LEDs in separable strips of three LEDs. That makes for a total of 30 RGB dots, which is presents no problem for a Rainbowduino.

My goal for this post is to record my process in putting this project together. I’m nowhere near done at the moment, but I’ll keep updating it as I go.


The plan for this project came together slowly – I knew that I wanted to make a large RGB LED display, and I had already bought one light strip to play with a year or so ago. I’m not sure how the Rainbowduino came across my radar, but it seemed perfect, because it could drive up to 64 RGB LEDs simultaneously, so could support up to 6 strips. However, the funding for the project chose to use 3, and I felt that that was more than enough to get the effect I was shooting for.

Because the strips run at 12 volts, and are each rated for 6 amps, I decided to use a spare PC power supply to provide power because it supplies a well-regulated voltage and plenty of current.

Finally, the Rainbowduino can operate in one of three ways: standalone mode, serial mode, or I2C mode. The second and third allow you to stream patterns to the Rainbowduino from another microcontroller or computer. However, I want this sun to stand on its own, so I’m planning on having it run in standalone mode. This means I’ll need a way of programming it with whatever patterns I want it to use. The Rainbowduino has a 6-pin ICSP plug, which will work perfectly with the AVR programmer I already have, Lady Ada’s UsbTinyISP.


To prepare for putting the whole display together, I wanted to test my LEDs, power supply and control board. I used an RGB driver based on a Teensy 2.0, a few FETs and a wall-wart (which I know works well with these strips) as a simple tester for the LEDs, and found no problems. The power supply also checked out, I took apart a single 4-pin plug to get the +12V and GND wires and checked the voltage with a multimeter. The reading was good and steady, but attaching it to the Rainbowduino caused one of the power-filtering capacitors to explode (which was unexpected, given the board is rated for 12V), but removing the damaged cap fixed the problem, and soon I had it powered up and lighting LEDs. I also connected the UsbTinyISP and used Avrdude to ensure I could program the Rainbowduino. (As an aside, the Avrdude part name for the ATMEGA328P is ‘m328p’, which took me way too long to figure out).

At this point I felt comfortable that I had everything I needed to put the display together (except for some sort of mounting board. However, the end of the weekend was drawing to a close, so I had to wait to get more done.

Steeling Myself

Before I prepared to cut my 3 strips into 30 smaller ones, and soldered 4 wires to each one, I decided to get a picture of what the final wiring would look like. This was a job for Cadsoft’s Eagle, the defacto-standard for making schematics and PCB layouts. Even though I’m planning on laying out the display by hand, with wires, I felt that having a reference for wiring the matrix would be worthwhile. I built a schematic to show the control layout for the LEDs, as a matrix, which is what the Rainbowduino is designed to drive. I then built a layout based on the schematic that corresponds (roughly, and not to scale) to how I’m planning to arrange the LED strips, although the footprints of all the parts are completely arbitrary. However, the pin layout of the headers on either side match the layout of those on the Rainbowduino, which will make it helpful when it comes time to connect all 120 wires.


Update, May 2: I’ve now finished wiring the matrix: I attached all of the strips to a piece of foamcore board using their adhesive backing and soldered all of the connections. Everything worked on the first try, and I flashed the code (rainbowduino_v1_0_4) from here. The demo patterns looked amazing, but sadly, shortly after powering it up (before Icould even get a video), something stopped working. Not only were the patterns not being displayed, but I couldn’t get my programmer to connect to the rainbowduino! Luckily, I emailed SeeedStudio, and one of their very helpful employe has promised me that a replacement is already on the way. Hopefully it arrives before the fifth, when I was hoping to set up the display on campus. Until it arrives, and I can replace the defective board on the display, enjoy the only two photos I took while it was working (before I flashed the new firmware onto it).

Final words

Despite the setback with my Rainbowduino, I went ahead with getting the display ready for this weekend, where (hopefully) it will be sitting in a central place, entertaining people with colorful patterns. To do this, I used a large zip-tie to strap the ATX power supply to the back of the piece of foamcore board, and used some more zip ties to position all of the wires out of sight, as well as to securely fasten the two wires running 12V to the display. All in all it looks good, and I’m excited to load some exciting patters onto it once my new control board arrives.

Also, this post is still in progress — check back soon for updates! Apologies for the lack of photos, they should be coming soon.

New Keyboard โ€” Reviewed!

Have you ever had one of those days when you bought a keyboard for no good reason? Well I did the other day, and ended up with an “Irocks Chocolate Key Style Slim Keyboard for Pc with Elegant Body”. It felt like a steal — I got it $12.99 with free two day shipping.

It is now replacing an older, wireless, but more compact keyboard from the same company, which, despite serving me well, had been getting flaky in age.

Hit the jump for another picture and a review/comparison of the two keyboards

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Update: Migratory Internet Junk

I know it’s taken me a long time to post this, but I received my box of migratory junk on May 10! I got box INTJ-7 which had been shipped out by a nice guy from San Diego. I don’t have a lot to say now (and no pictures) but I’d like to share some of what I got out of it. Perhaps my biggest find was right on top: a Hand Held Products IT4410 2D barcode scanner. On the product page I found theร‚ย manual manual (pdf link) which explains all of its features.

HHP 4410HD Barcode Scanner

It turns out that the scanner emulates a PS/2 keyboard and will read almost any 1D or 2D barcode symbology. After a few hijinks with a loose ribbon cable and flaky PS/2 support on my computer I got the scanner working perfectly. I was even able to change its configuration by scanning barcodes from the manual displayed on my LCD (though I don’t know if it will work with glossy screens — mine is matte).

I’m planning on putting up a more complete summary of what I’ve found, but here are a few other things that caught my eye:

  • A solenoid-controlled proportional valve for small pneumatics or hydraulics.
  • A bag of large rubber grommets, one of which I cut up to replace the feet on a table lamp.
  • Three matched stepper motors.
  • A worm-gearbox connected to a large motor with integrated optical encoder.
  • A wide variety of IR LED/phototransistor gates.
  • A pile of 1.8V, 2.5V and 3.3V voltage regulators.

Stay tuned for pictures and more details on what I’m taking and what I’m going to do with it.

Heads Up: Migratory Internet Junk

If you haven’t heard of TGIMBOEJ (The Great Internet Migratory Box Of Electronics Junk), you should definitely check it out. The basic idea is that a box of random electronic junk gets shipped between makers and tinkerers, each of whom take something and contribute something to the box, and document what they end up doing.

To make a long story short, I was recently offered a chance to receive one of these migratory lending libraries, so expect to see something in this space about it soon.