Any designs for a cheap x-y position sensor?

[rickman]

I was amazed at the accuracy of the cheap Logitec mouse. I paid $1.
for the mouse at surplus outlet. Just turn the software to 'linear'
get rid of that auto speed detect. move it around on a sheet of paper
while recording the 'clicks' The backlash in the plastic gearing was
easily removed and compensated for. amazing to me was the
repeatability of going one way and then back the other way, the
repeatability was more than good enough. From memory the 'distortion'
from x to y was less than 1-2% !! couldn't believe that one. Plus,
there was already a C/C++ library program to ask for the position of
the mouse - part of Windows environment. so like for only $1 I got
this small range x-y position sensor that had ?? accuracy. From memory
it was better than a few mils, have to go check my archives for that
info. Better not say without checking.

I figured you were talking about an optical mouse. I suppose the
mechanical mice can be more accurate, linear, etc.

What did you use it for?

Rick

 

[[email protected]]

The speed of sound doesn't depend on pressure, just temperature and mean
molecular weight.

The real downside is wind and temperature changes.  Unlike light, sound
is an oscillation in a physical medium, and when the medium moves, the
rest-frame speed of sound changes.  The speed of sound at 20C is about
343 m/s (perhttp://www.sengpielaudio.com/calculator-speedsound.htm),
or about 770 mph.  Thus a 2-mph breeze will cause a phase error of
0.25%.  Similarly, a 2-degree temperature difference will cause the
speed of sound to change by 0.5 * 2/293 = 0.34%. (The factor of 1/2
comes from the binomial expansion of the square root--v goes as sqrt(t)).

Cheers

Phil Hobbs

yeh, you can get ultrasonic anemometers

http://www.gill.co.uk/products/anemometer/principleofoperation.htm

-Lasse

 

[Robert Macy]

I figured you were talking about an optical mouse.  I suppose the
mechanical mice can be more accurate, linear, etc.

What did you use it for?

Rick

cheap x-y psoition sensor

 

[rickman]

cheap x-y psoition sensor

Yeah, well I meant what were you measuring the position of? What was
the application?

Rick

 

[Robert Macy]

Yeah, well I meant what were you measuring the position of?  What was
the application?

Rick

I know, just giving you a hard time.

for keeping track of the position of a small reflective probe used in
NDE Instrumentation. To keep track of where the data comes from as a
function of x-y position over the surface of a piece of aircraft
structure. For me, z axis was NOT necessary, because the algorithm
inherently shifts vertical for probe's vertical position anywhere from
contact to 1/2 inch above !!

 

[hamilton]

I know, just giving you a hard time.

for keeping track of the position of a small reflective probe used in
NDE Instrumentation. To keep track of where the data comes from as a
function of x-y position over the surface of a piece of aircraft
structure.

So its a smooth surface.

I wondered.

hamilton

 

[Robert Macy]

The cheapest USB color camera on ebay/amazon is $1. I've run 75 feet
to a camera, two active USB extenders and some passive cables.
Ethernet cams can run any distance. The software will be the hard
part.

Where to get $1 USB cameras??

It just dawned on me how to do simple SW conversion!