Tag: tilt alarm

(PB) Using the Thinkpad Accelerometer

Posted by on January 29, 2013

So I recently got a proper Thinkpad and I was wondering how to interface with the accelerometer to obtain data from it. First of all, I had a look around and it seems the ADXL320 is used in most models, it’s a Low Power, 3-Axis ±5 g MEMS Accelerometer manufactured by Analog Devices.

There are, at least on Windows, two possible interfaces. One is through a device manager, the other is directly through a DLL exposed by Lenovo.

I had yet another look around and found a few snippets in C# by Ben Suter. Decided to port the code and give it a go, instead of looking any further. Despite the fact that I had already exported the function names of the DLL (using my good ol’ dllspyr) I just couldn’t bother looking any further. I had to add the z value, since it was originally ignored. Perhaps because previously a mere 2 axis tilt sensor was used?

The other method involves getting a handle of “ShockMgr” with createFile(); setting up by DeviceIoControl(); and then reading through the data. This makes it easier to validate if the “service” is available, because the DLL could be exposed but non functional, for example.

Da codez:

Here’s the preliminary test code, implementing a crude alarm system:

The status code is interpreted by another function, which I’m not using at the moment but the author had guessed the threshold values and addressed a name for each, from the known possible states exposed by Lenovo.

What now?

I’m going to clean up the code and start making use of this feature, I mean, why not?

As for a proper alarm, you’d have to manage the mute and volume settings plus instead of comparing against the baseline values you’d have to implement a threshold. I’m aware that they’ve issued an application that does exactly this, but I’m not a fan of big resident bloatware — plus where’s the fun in that?

Anyway, that’s all for now!