Help needed - ADXL202
Archiver
Posts: 46,084
I am looking for someone to correspond with concerning the use of the
ADXL202 two axis acceleromenter as an accurate tilt sensor for measuring
the inclination of a small telescope. I have been struggling with the
geometry of the tilt sensor. I am able to reliably retrieve the angular
data from the '202 but I don't seem to be able to compute the tilt using
the vector of the two axes. I believe that it is necessary to use both
axes to compute the tilt because I have no reliable way to insure that
the accellerometer is accurately aligned to the telescopes pointing axis.
I am using a test rig of a '202 mounted on a 'scope, more or less aligned
to the azis I am attempting to measure the tilt of. I am able, by mechanical
means to measure this axis's tilt to around 1/2 degree.
I guess what I am saying here is that I need some assistance in the
geometrical calculations, not the gathering of the raw data.
I have read in a recent issue of Circuit Celler that it is possible to
achieve tilt angle accuracys of 0.1 degrees over the range of 0 to 90
degrees. I find this hard to believe. I would be happy to be able to
measure the tilt to 1/2 degree.
Any enlightenment will be GREATLY appreciated.
TIA
Vic
________________________________________________________
Victor Fraenckel - The Windman vfraenc1@n...
KC2GUI www.windsway.com
Home of the WindReader Electronic Theodolite
Read the WIND
"Victory at all costs, victory in spite of all terror, victory however long
and hard the road may be; for without victory there is no survival."
- Winston [noparse][[/noparse]Leonard Spencer] Churchill (1874 - 1965)
Dost thou not know, my son, with how little wisdom the world is governed?
-Count Oxenstierna (ca 1620)
ADXL202 two axis acceleromenter as an accurate tilt sensor for measuring
the inclination of a small telescope. I have been struggling with the
geometry of the tilt sensor. I am able to reliably retrieve the angular
data from the '202 but I don't seem to be able to compute the tilt using
the vector of the two axes. I believe that it is necessary to use both
axes to compute the tilt because I have no reliable way to insure that
the accellerometer is accurately aligned to the telescopes pointing axis.
I am using a test rig of a '202 mounted on a 'scope, more or less aligned
to the azis I am attempting to measure the tilt of. I am able, by mechanical
means to measure this axis's tilt to around 1/2 degree.
I guess what I am saying here is that I need some assistance in the
geometrical calculations, not the gathering of the raw data.
I have read in a recent issue of Circuit Celler that it is possible to
achieve tilt angle accuracys of 0.1 degrees over the range of 0 to 90
degrees. I find this hard to believe. I would be happy to be able to
measure the tilt to 1/2 degree.
Any enlightenment will be GREATLY appreciated.
TIA
Vic
________________________________________________________
Victor Fraenckel - The Windman vfraenc1@n...
KC2GUI www.windsway.com
Home of the WindReader Electronic Theodolite
Read the WIND
"Victory at all costs, victory in spite of all terror, victory however long
and hard the road may be; for without victory there is no survival."
- Winston [noparse][[/noparse]Leonard Spencer] Churchill (1874 - 1965)
Dost thou not know, my son, with how little wisdom the world is governed?
-Count Oxenstierna (ca 1620)
Comments
Tilt axis geometry is explained in detail in the Analog Devices
application notes for the '202, available on the AD website. Note
particularly that the nonlinearity of the sine function implies the
greatest measurement accuracy when the axis is aligned perpendicular to
the gravitational vector, and least accuracy when aligned along the g
vector. But because the '202 is a 2-axis device, with axes
perpendicular, use of both axes is recommended. As to geometrical
calculations, they are basically sine and cosine functions, which could
be done by sending the '202 data to a PC.
Dennis
Dennis P O'Leary PhD
President
WSR, Inc.
Pasadena CA
"Wagner's music is not as bad as it sounds." -- Mark Twain
Original Message
From: Vic Fraenckel [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=4RnGtBZXBC4FOvg7VfMf5zOz-8pH8SYLuxOrepOf8YdPpWufV6SwizkuJceXx0EM3NLygSM7XlKTsaU]vfraenc1@n...[/url
Sent: Sunday, February 16, 2003 6:02 PM
To: BasicStamps
Subject: [noparse][[/noparse]basicstamps] Help needed - ADXL202
I am looking for someone to correspond with concerning the use of the
ADXL202 two axis acceleromenter as an accurate tilt sensor for measuring
the inclination of a small telescope. I have been struggling with the
geometry of the tilt sensor. I am able to reliably retrieve the angular
data from the '202 but I don't seem to be able to compute the tilt using
the vector of the two axes. I believe that it is necessary to use both
axes to compute the tilt because I have no reliable way to insure that
the accellerometer is accurately aligned to the telescopes pointing
axis.
I am using a test rig of a '202 mounted on a 'scope, more or less
aligned to the azis I am attempting to measure the tilt of. I am able,
by mechanical means to measure this axis's tilt to around 1/2 degree.
I guess what I am saying here is that I need some assistance in the
geometrical calculations, not the gathering of the raw data.
I have read in a recent issue of Circuit Celler that it is possible to
achieve tilt angle accuracys of 0.1 degrees over the range of 0 to 90
degrees. I find this hard to believe. I would be happy to be able to
measure the tilt to 1/2 degree.
Any enlightenment will be GREATLY appreciated.
TIA
Vic
________________________________________________________
Victor Fraenckel - The Windman vfraenc1@n...
KC2GUI
www.windsway.com
Home of the WindReader Electronic Theodolite
Read the WIND
"Victory at all costs, victory in spite of all terror, victory however
long and hard the road may be; for without victory there is no
survival."
- Winston [noparse][[/noparse]Leonard Spencer] Churchill (1874 - 1965)
Dost thou not know, my son, with how little wisdom the world is
governed? -Count Oxenstierna (ca 1620)
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
from the same email address that you subscribed. Text in the Subject
and Body of the message will be ignored.
Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
for 3 axis sensing in virtual arrays. The accuracy of tilt depends on your
setup of the interface circuit, Analog Devices has a tool to give circuit
specs for a given sensitivity
http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTool\
s/accelerometer/adxl202.html
If you have any other questions, i'd be happy to help
Christian
Intelligent Microsystems
>From: "Vic Fraenckel" <vfraenc1@n...>
>Reply-To: basicstamps@yahoogroups.com
>To: "BasicStamps" <basicstamps@yahoogroups.com>
>Subject: [noparse][[/noparse]basicstamps] Help needed - ADXL202
>Date: Sun, 16 Feb 2003 21:02:07 -0500
>
>I am looking for someone to correspond with concerning the use of the
>ADXL202 two axis acceleromenter as an accurate tilt sensor for measuring
>the inclination of a small telescope. I have been struggling with the
>geometry of the tilt sensor. I am able to reliably retrieve the angular
>data from the '202 but I don't seem to be able to compute the tilt using
>the vector of the two axes. I believe that it is necessary to use both
>axes to compute the tilt because I have no reliable way to insure that
>the accellerometer is accurately aligned to the telescopes pointing axis.
>
>I am using a test rig of a '202 mounted on a 'scope, more or less aligned
>to the azis I am attempting to measure the tilt of. I am able, by
>mechanical
>means to measure this axis's tilt to around 1/2 degree.
>
>I guess what I am saying here is that I need some assistance in the
>geometrical calculations, not the gathering of the raw data.
>
>I have read in a recent issue of Circuit Celler that it is possible to
>achieve tilt angle accuracys of 0.1 degrees over the range of 0 to 90
>degrees. I find this hard to believe. I would be happy to be able to
>measure the tilt to 1/2 degree.
>
>Any enlightenment will be GREATLY appreciated.
>
>TIA
>
>Vic
>
>
>________________________________________________________
>
>Victor Fraenckel - The Windman vfraenc1@n...
>KC2GUI
>www.windsway.com
>
> Home of the WindReader Electronic Theodolite
> Read the WIND
>
>"Victory at all costs, victory in spite of all terror, victory however long
>and hard the road may be; for without victory there is no survival."
>- Winston [noparse][[/noparse]Leonard Spencer] Churchill (1874 - 1965)
>
>Dost thou not know, my son, with how little wisdom the world is governed?
>-Count Oxenstierna (ca 1620)
>
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
>from the same email address that you subscribed. Text in the Subject and
>Body of the message will be ignored.
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
_________________________________________________________________
Help STOP SPAM with the new MSN 8 and get 2 months FREE*
http://join.msn.com/?page=features/junkmail