By Michael Stanley
Originally posted on Freescale’s The Embedded Beat Blog
In my last post (“Degrees of freedom vs. axes”) we discussed some basic terminology for sensor fusion. This time around, we get to put that lesson into practice as we examine Freescale’s recent technology announcement of a full featured reference platform for Windows®8 sensor fusion.
If you are a regular reader, you’ll know by now that I am fascinated by sensors and sensor fusion software. These are the technologies that let us interface with our electronic toys with a simple tap, swipe or gesture. So I was energized last week when Freescale announced development of a 12-axis, sensor fusion reference platform for Microsoft® Windows®8. I was at the kickoff meeting last year between Microsoft and Freescale, and I’ve been watching the system evolve in our offices since. We’re not quite ready to ship boards to the general market, but we’re excited and want to share our plans and status with you.
Figure 1: Freescale Microsoft® Windows® 8 Sensor Fusion Data Flow
From an information flow point of view, the board looks something like Figure 1. Our 12 axes of sensor input information are:
- X/Y/Z Accelerometer
- X/Y/Z Gyroscope
- X/Y/Z Magnetometer
- Barometer (air pressure)
- Ambient Light
Each of these is available in one form or another as outputs of the system, but more importantly, the system also computes board orientation. This can come in one of several forms:
- rotation matrix
- Inclinometer Euler angles
You also get compass heading out of the mix. From a hardware perspective, the board looks like the block diagram in Figure 2.
Figure 2: Functional Level Block Diagram
Sensor fusion software is pre-installed in the MCF51JU128 flash memory. To utilize the board, you will need a Windows® 8 enabled computer or slate to act as host:
- If your device is already equipped with sensors, you’ll need to disable them via the device configuration screens in Windows 8. If your device isn’t already sensor equipped, you can skip this step.
- Plug the development board into your device’s USB port.
- You are done!
Pure plug & play. That’s because Microsoft has defined an “HID over USB” protocol for communications with a sensor fusion subsystem. The Freescale board talks the same language as Windows 8. And since Freescale will be publishing the full schematic and bill of materials, adding motion sensor capability to your Windows PC or slate couldn’t be easier.
Once the boards start shipping, you’ll be able to download user manual, schematics and CAD files from the Freescale web site. The user manual will include instructions for customizing the software for use on your PCB, since placement orientations for sensors will vary from board to board. Don’t worry. The process should be relatively painless.
Freescale will also supply a basic sensor application that you can use to test out your sensor subsystem. The application gives you a visual compass display, along with either a 3D view of a virtual gyroscope (Figure 3) or a window into a virtual room (Figure 4). You can see accelerometer, gyroscope (which Microsoft refers to as a “gyrometer”) magnetometer, ambient light sensor, temperature and air pressure readings.
Figure 3: Gyroscope (wired) view
Figure 4: Virtual Room (attached) view
Microsoft has a rigorous certification process which is encapsulated in their “Windows Hardware Certification Kit”, or “WHCK”. The WHCK specifies passing sensor test criteria and ensures hardware/software compatibility. Microsoftupdates the WHCK on a regular basis, and Freescale continuously tests its solution using the WHCK. Final certification of the kit will occur after Microsoft releases their final WHCK. This will occur before the Windows 8 OS release. I can tell you that the software is passing most of the WHCK today, with only a few open issues which we expect to resolve shortly.
We expect Freescale’s Windows 8 reference design to be available in late 3rd quarter, so you’ll have to wait a bit. But we wanted you to know it’s coming, and it’s real.
Finally, on another topic, if you happen to be attending the Freescale Technology Forum in San Antonio next week, and you see a fellow who looks a bit like the picture alongside this post, please come up and say hello. I would love to talk with you about your sensor needs.
- Microsoft 2001 Build Conference Materials
- Windows 8 Release Preview Product Guide for Developers
- The HID Class Driver for Sensors
- Integrating devices, printers, and sensors
- Integrating Motion and Orientation Sensors