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wacofishman
01-15-2007, 08:29 AM
I want to build a wind direction sensor using a Stamp, and understand that most use low-torque potentiometers. I've read a lot about a dead zone, and am very new to electronics, so shopping for a pot at Digikey or Jameco is a little intimidating since they all look the same. Can anyone recommend a good pot for this application, or at least point me to a resource for how to understand the labeling?

Thanks,
Steven

Robert Kubichek
01-15-2007, 09:00 AM
wacofishman said...
I want to build a wind direction sensor using a Stamp, and understand that most use low-torque potentiometers. I've read a lot about a dead zone, and am very new to electronics, so shopping for a pot at Digikey or Jameco is a little intimidating since they all look the same. Can anyone recommend a good pot for this application, or at least point me to a resource for how to understand the labeling?

Thanks,
Steven


There also was a 1-wire solution using optical encoding, and also magnetic position sensing... http://forums.parallax.com/images/smilies/turn.gif

1-wire weather station; www.maxim-ic.com/products/ibutton/weather/1wire_weather_stn.pdf (http://www.maxim-ic.com/products/ibutton/weather/1wire_weather_stn.pdf )
Distributer of 1-wire weather products; www.aagelectronica.com/aag/index.html (http://www.aagelectronica.com/aag/index.html )


Bob http://forums.parallax.com/images/smilies/scool.gif

wacofishman
01-15-2007, 09:44 AM
Bob,

Thanks for the link. I was really hoping to achieve greater accuracy with the direction of the wind -- within a few degrees. I understand the pot is the way to go if I can find one that has no stop or dead zones.


Steven

Franklin
01-15-2007, 10:12 AM
What application are you designing that needs that ammount of precision?

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- Stephen

wacofishman
01-15-2007, 10:17 AM
It's for a personal weather station, and my desire to be as accurate as possible. http://forums.parallax.com/images/smilies/yeah.gif


Steven

Robert Kubichek
01-15-2007, 10:34 AM
wacofishman said...
Bob,

Thanks for the link. I was really hoping to achieve greater accuracy with the direction of the wind -- within a few degrees. I understand the pot is the way to go if I can find one that has no stop or dead zones.


Steven


An optical encoder, would easily give you the accuracy you need,
you can hack an encoder strip from an injet printer,
or print an encoder disk with the degree of accuracy you need...
A quadature encoder mounted on the vane shaft will do the same....
A continuous rotation pot is really 2 pots in one, with the dead spots 180 degrees apart....
A continuous rotation pot will also add friction making it harder to read direction of light winds,
and it will wear out faster than an optical encoder.
There has been some encoder code posted in the forum if I remember right..

Bob http://forums.parallax.com/images/smilies/scool.gif

wacofishman
01-15-2007, 10:35 AM
Hmmm. I found this....

http://www.inscale-potentiometers.co.uk/potentiometer_l2.php?prodid=2272&view+l2=View+Details+%3E&prodcode2=RSC+2201&cat=Angle+Sensors%2C+Non+Contacting&family=RSC2200&title=Angle+Sensors%2C+non-contacting
and
http://www.inscaletechnology.co.uk/potentiometers/aw360ze.html


Steven

Tracy Allen
01-15-2007, 11:23 AM
fascinatingelectronics.com/weatherinst.html (http://fascinatingelectronics.com/weatherinst.html)

I heard at one time that they would sell that dual wiper potentiometer they use in a wind vane as a separate item and at a very reasonable price. Their wind vane and anemometer construction is very clever.

I don't know of any other potentiometer that combines low torque, continuous rotation and negligable dead band, avaialbe from standard sources like Digikey and Mouser. It is a specialized item and can cost $$$. The potentiometer is the achilles heel of wind monitoring, because it has a finite life. All that back and forth rubbing motion wears it out.

There are alternatives, but they are either more complicated or have another down side. One technology I have been watching (but haven't had time to try) are the angular displacement magnetostrictive sensors from Honeywell, www.position-sensors.com/ (http://www.position-sensors.com/), e.g. HMC1512 -- $7 from digikey. They require some signal conditioning and power, but the power can be pulsed without losing track of where you are. The app notes show how to combine one HMC1512 with one Hall effect sensor to cover 360 degrees with near 0.1 degree resolution.

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Tracy Allen
www.emesystems.com (http://www.emesystems.com)

Phil Pilgrim (PhiPi)
01-15-2007, 01:38 PM
There's also the Melexis MLX90316 (http://www.melexis.com/ProdMain.aspx?nID=566), which is carried by DigiKey.

-Phil

John Abshier
01-15-2007, 11:55 PM
For $29 or a few dollars more with ball bearings US Digital sells and absolute position encoder. Output is either an analoge voltage or a pulse with.
http://www.usdigital.com/products/ma2/

wacofishman
01-16-2007, 01:18 AM
OhhahHhh... I'm really liking the absolute encoder. http://forums.parallax.com/images/smilies/idea.gif


Steven

Phil Pilgrim (PhiPi)
01-16-2007, 02:04 AM
Be sure to check the environmental specs — especially the R.H. limits. One advantage to rolling your own is that you can completely seal the electronics, while the rotating magnet can be out in the elements. Otherwise, you'd have to use a shaft seal, which will increase the minimum turning toque considerably.

-Phil