WowWee Rovio Hack: Head-Mounted LED LightsPosted by Rudolph on Monday, 20 October 2008
The Illumination of Rovio
Trundling down the uncharted vastness of the Dark Hallway our Hero, the Rovio, encounters an unknown, large, assailant. Rovio lifts its head to get a better view of this creature's face. Being in the Dark Hallway, the Great Operator instructs Rovio to turn on its headlight. The electrons flow, the LED brightens, and a bright bluish-white glow envelopes the toes of Rovio's potential nemesis... but Rovio is unable to identify the assailant's facial features. The Great Operator grabs up the Rovio and a screwdriver and goes about adding some headlights to Rovio's camera.
If you've spent much time with the Rovio in a semi-darkened room, you'll no doubt have noticed that in some situations, you might want to have even more light available. It feels natural to me to have the headlights mounted in such a way they could light what the camera is pointed at, as well. So, I decided to add a pair of LEDs to the head on either side of the camera. Read on for the gritty detail, and please remember that hacking your Rovio will definitely void your warranty!
List O' Materials
- Soldering pencil
- 22g solid and stranded wire in black and red
- Two bright white LEDs
- One 2N2907 PNP Transistor
- Two 5.6 Ohm resistors
- One 2.2k resistor
- Small bit's of stripboard (optional)
Most of these materials I had lying about. A mediocre source for cheap white LEDs is your local dollar store; I found cheesy little LED flashlights for, surprise, a dollar. Each flashlight had three LEDs in it and ran on three AAA batteries (totalling 4.5 volts). The transistor is most likely in stock at the local Radio Shack for 79 cents, or a 15 pack of various PNP transistors is $2.59 and includes five of the 2907 (so you can screw up a few times!) plus have a few left over for future projects.
The Opening of Rovio
Obviously, to begin this project Rovio needs to be opened up. With the Rovio turned on, lift the "head" to the full up position, then push the power button and turn it back off. Flip Rovio over (it works fairly well to hold it on your lap with the head stalk between your knees) and remove the battery. With the robot still inverted, remove the six phillips screws closest to the outside edge and store them (coffee cups work well, as do empty egg cartons) Flip it back over, set it on the table, and seperate the two halves of the robot. There will be a wad of cabling preventing the top half from being moved too far from the bottom.
The Circuit Part
There are two parts of the bottom half that are of interest to this project. Both are outlined in a yellowish color below.
The first is the light array in the "chest" (bottom middle of photo). The outside bulbs are Rovio's InfraRed "Radar". The center bulb is Rovio's default headlight, which I tapped into for control of the new headlights.
A bit of poking about told me the white wire coming from the LED is what I was after. It is the ground for the default headlight, which is apparently switched via the brain board (upper right in photo.) There is a reasonable chance that the existing circuit could handle that extra load of two headlights. For the sake of overkill I used it to switch a new circuit. Since it's a ground to the board, I used a PNP transistor to switch the ground of the new lights. I snipped the white wire near the middle (taking care to leave room to put it back together if all this failed) and connected the board end of it to the base of the transistor through the 2.2k Ohm resistor.
The second area is the power supply board (left middle of photo). This is what the battery and charging terminals are connected to. There are a few convenient empty holes in this board which I soldered directly into. Below is the board in original form, then after I soldered a nice black wire into a ground hole. The other end of the black wire goes to the Emitter of the transistor.
Naturally I failed to get a photo of a red wire soldered to a positive hole, so you'll have to imagine that part. The red wire will supply power to the LEDs in the Rovio's head.
The Tricky Part
After removing four screws from the underside of Rovio's head, I found there's not a whole lot of space left over inside. However, there are two perfect little empty spots on either side of the camera just begging to be filled with extra lighting.
To power the lights in this location I had to fish two wires up through Rovio's neck. Indeed, this was the most fun of the whole project, and it took me about thirty minutes to get the wires into place. I'm pretty sure that further disassembly of the neck could have made this easier. I found it much easier to stuff the wires, one at a time, up from the bottom of the neck (rather than down through the head).
Once the red and black wires were through the neck and into the head area I soldered the red wire directly to the positive leads of the LEDs (in parallel via a Y split). The black wire is connected to the two LED negative leads via the 5.6 Ohm resistors. After a bit of pushing and prodding wires into place the LEDs sit fairly nicely and it was time to cut the plastic housing to accomodate them.
Now it's time to stuff all this new wiring into place and close up the Rovio. This was the second most fun part of the project. Take care to not crush any of those skinny little wires, they probably wouldn't like it much. Once everything is in place, screw it all together, put the battery back in, and fire it up. Next time you hit the Headlight button in the UI you'll be able to blind whoever Rovio is looking at!
Please visit the attached image gallery to see a few before and after shots from the Rovio's camera. Also in the gallery are a few more higher-resolution pictures of Rovio internals, the wiring diagram of the final circuit, and a shot or two of the outside final look of this mod.
Always breadboard your circuit first, so a dead LED doesn't cause grief. That was highly annoying.
I chose 5.6 ohm resistors for the LEDs based off the 4.63 volts I found after the transistor was wired up. I'm assuming the voltage drop is due to grounding through the transistor, and the transistor switching through the brain board. Your mileage may vary.
Mine is set up to replace the existing headlight, since having it still light would be a bit superfluous. I did mess with it a bit though and couldn't get the original LED to light reliably. I believe this is due to the differences between it and the new LEDs I put in the head being run off the same circuit. This may be solveable by using different resistors on the new LEDs.
I added a bit of heat shrink to the outside of the LEDs. The idea was to prevent side light from washing out the Rovio's camera. It seems to have worked, but I can't prove it was necessary.
In retrospect, choosing bright white LEDs from the dollar store isn't such a hot idea. Because they're cheap, there is a noticeable blue tinge to everything. A higher quality LED would emit a "cleaner" white light.