The "Foculus Rift" part 2: Reverse engineering the motion tracker

The function of the motion tracker is to estimate the current roll, pitch and yaw angles of the head mounted display (HMD), which allows the 3D game to know what you are looking at and render the scene accordingly.

The original Rift uses the following configuration (as nicely shown by ifixIt):

• Invensense MPU-6000, gyroscope and accelerometer sensor
• Honeywell HMC5983, magnetic field sensor / compass
• ST  32F103C8, ARM 32 bit microcontroller (with USB connection)

The "Foculus Rift" part 1: Building a Head Mounted Display

Some time ago I read BitCortex's manual on building a homemade "head mounted display" (HMD), just like the Oculus Rift:
http://bitcortex.com/oculus-libre-open-source-hmd-inspired-by-oculus-rift/

The concept is surprisingly simple and low tech. A LCD panel presents seperate pictures to the left and right eye, lenses are used to place the panel close to the eyes and hence produce a wide field of view (FOV). What I read about these very simple homemade glasses made me curios. The people on the mtbs3d forums (the birth-place of the rift) claimed that the 3D effect is fantastic and the head tracker allows the games to become extremely immersive.

It was clear, I had to try to build some of these fancy 3D goggles.
These posts will document the progress I have made, the problem I encountered and the improvements I came up with along the way.

Microwave filters for dummies

For a recent project I needed a bandpass filter in the microwave range, made from non-magnetic materials. Remembering this very nice article from Paul Wade, I decided to give it a shot and roll my own. As the results turned out to be spectacular, I had to share this experience.

The green flatscreen

Well, what to do with a perfectly fine flatscreen, found in the trash with a blown backlight?

Convert it to solar power of course!

It works surprisingly well as a secondary monitor. Provided there is enough sunlight, the image is quite crisp and colourful. And the best thing is: The brighter the sun, the better it looks -- while the picture on an ordinary monitors becomes unrecognisable.

Some nice "Hidden Sector Photon" fieldplots

Some 3D plots I have done recently for a presentation. They were done with Python and Mayavi. They show how a hypothetical hidden photon field would look like. The emitting structure is a microwave cavity, with a strong electromagnetic field inside. This field is the driving force for the hidden photon field which can penetrate the cavity walls and propagate into space. Unfortunately you can not see the cavity geometry itself in these pictures.

You don't need to understand any of this, just enjoy the visuals...

A power amplifier for the serious garage door opener

While my serious garage door opener works nicely and reliably, it's output power is "only" 10 dBm (10 mW). It is able to open the garage door from about 100 m -- this is clearly not enough.

So I thought an impressive looking garage door opener needs an impressive amount of RF output power as well. And I found a wonderful solution to that problem, the SKY65116 chip module.

It provides up to 2 W of output power from 390 - 500 MHz, 30 dB of gain and its input and outputs are matched to 50 Ohm. In fact it contains a third matching circuit between the internal pre- and power-amplifier  It can be put into standby mode drawing only a few uA and thus can be left connected to the battery. When running at full blast it draws 1.2 A at 3.6 V, so its efficiency is about 50 %. Not bad at all!

The serious garage door opener

Garage door openers are handy little gadgets. Most of them are cheap chinese plastic crap though. This one definitely isn't. It started by collecting parts from my favorite electronics shop: the dumpster.

An old emergency shutdown switch makes the perfect case with a seriously big red button.