From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261608AbVHANJF (ORCPT ); Mon, 1 Aug 2005 09:09:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261803AbVHANJF (ORCPT ); Mon, 1 Aug 2005 09:09:05 -0400 Received: from styx.suse.cz ([82.119.242.94]:8407 "EHLO mail.suse.cz") by vger.kernel.org with ESMTP id S261608AbVHANJD (ORCPT ); Mon, 1 Aug 2005 09:09:03 -0400 Date: Mon, 1 Aug 2005 15:09:02 +0200 From: Vojtech Pavlik To: "linux-os (Dick Johnson)" Cc: Paulo Marques , Jan Engelhardt , Lee Revell , abonilla@linuxwireless.org, linux-kernel@vger.kernel.org, hdaps devel , Yani Ioannou , Dave Hansen Subject: Re: IBM HDAPS, I need a tip. Message-ID: <20050801130902.GA23949@ucw.cz> References: <1122861215.11148.26.camel@localhost.localdomain> <1122872189.5299.1.camel@localhost.localdomain> <1122873057.15825.26.camel@mindpipe> <42EE1324.10304@grupopie.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.6i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 01, 2005 at 08:55:53AM -0400, linux-os (Dick Johnson) wrote: > > Jan Engelhardt wrote: > >>> So in order to calibrate it you need a readily available source of > >>> constant acceleration, preferably with a known value. > >>> > >>> Hint: -9.8 m/sec^2. > >> > >> Drop it out of the window? :) > > > > No, no. Constant gravity (like having the laptop sitting on the desk) > > "feels like" constant acceleration. > > > > Dropping it out of the window should measure 0 m/sec^2, because the > > accelerometer is not working on an inertial referential (I hope this is > > the correct term in english...). For the accelerometer, this is just > > like the feeling of free falling inside an elevator: no gravity :) > > > > -- > > Paulo Marques - www.grupopie.com > > You need a centrifuge or something that works like one. You can > make one and you can calibrate it using simple techniques. Not at all. It's enough to let the laptop lie on the table for [0,0]G calibration, then put sequentially it on all the four sides for [-1,0]G, [1,0]G, [0,1]G, [0,-1]G calibration. >>From these five measurements you have both the zero point and the slopes, including a good error estimate. I've done that before when toying with IMUs. -- Vojtech Pavlik SuSE Labs, SuSE CR