i need to make effectively a weathervane. i need to measure wind direction. I think the easiest way is with a potentiometer, but my understanding is that they can't spin past a certain point. are there pots that can? i can't use an encoder because i need absolute position, and don't care about rate of change. i guess an absolute encoder would work too, but i haven't seen them for sale at the usual suspects (sparkfun, etc.)
You can indeed buy potentiometers that have no stops, but the ones I know about have a small "dead zone" where they do not give any position information (that is, the wiper does not contact the resistance element). Absolute shaft encoders tend to be pretty expensive. The higher the resolution, the more expensive. Check surplus outlets and Ebay for possible reasonable deals.
Here is a discussion of the relative merits of the two approaches: Potentiometer vs. Encoder - Sensors - Chief Delphi
I wonder could you stack two non-stop pots on top of each other on the same shaft and arranged so that the dead zones are on opposite sides?
Could you use a multi turn pot and have a small electric motor to "unwind" the vane when necessary?
...R
The easiest way is with an absoloute hall effect shaft encoder, these are quite cheap and give you 10 bit resoloution.
You connect a magnet to one end and position it just above the chip. I have used an AS5040 to do this.
The free spinning pots are meant for servo controllers and can be very pricy.
look at encoders. they also have the ability to offer exact position and are free spinning.
I do not think potentiometers offer the best solution, I am not sure how they would go from say, 0 to 1,000 then back to zero.....
you might google home made weather vane and see how others have done it.
Yes I made one like that back in 86.
http://www.doc.mmu.ac.uk/STAFF/A.Wiseman/Acorn/BodyBuild/BB86.html
For the text.
Diagrams attached.
just a note, but you do not need to see through the encoder, you can see reflected white or non-reflected black and have the sensors on the same side.
one style would be a QRD1114
you can use pretty much any light source and receiver with those laser printed white/black disks,.
i think either the hall effect sensor or a pot is the way to go for me.
the additional info here is that this is going into an RC sailboat, so size and power consumption are important. also - I don't care about the dead zone because there's a roughly 60* no-go zone for the boat, and I just need to know that i'm in the dead zone.
thanks
Grumpy_Mike:
The free spinning pots are meant for servo controllers and can be very pricy.
Depends on the seller...
I shop at a local place for surplus electronics parts where sometimes they know their stuff, but often-times they don't. For instance, one time they sold me a thousand feet of multimodal fiber for $20.00, thinking it was wire. I have no idea what I'll use it for; I certainly can't afford the termination tools...
In the case of servo pots - I ran across several inside a drawer in the back - nice Bourns units, smooth running, nearly brand new. They sold me six for a dollar each.
Similarly, I find on occasion these Bourns optical quadrature shaft encoders laying around there, I typically get those for a dollar each, too.
The goofy thing is, none of this stuff is marked - so I hand it over, ask them "how much for it" - they take it in the back office, some guy looks it up, then they come back and sell them to me for little to nothing; but who am I to argue? If that's what they want to sell the stuff for, far be it for me to suggest otherwise!
That said, there have been times I have paid more for stuff there than what it was really worth, but even then, I think I come out ahead overall (I've also been shopping there for 20+ years).
In general, though - yeah, buying such potentiometers online or otherwise you'll spend a pretty penny - no doubt.
kolosy:
i need to make effectively a weathervane. i need to measure wind direction. I think the easiest way is with a potentiometer, but my understanding is that they can't spin past a certain point. are there pots that can? i can't use an encoder because i need absolute position, and don't care about rate of change. i guess an absolute encoder would work too, but i haven't seen them for sale at the usual suspects (sparkfun, etc.)
I read about a rather interesting method of wind direction sensing. The fellow used a regular anemometer (homemade out of ping pong balls), but on one of the cups, he had a small 'ear' that stuck out parallel to the arm holding the cup. He used a printed disk and photocell detector, and the index (north) was a missing mark such that the first first mark after a long gap was the north reference.
The ear caused a somewhat sinusoidal speed variation in the wind speed, and he calibrated the speed, taking into account the slowing and speeding up of the anemometer, as well as figuring out which direction the wind was blowing from the position of the ear.
I always wanted to try one like that. Perhaps some day I will, though an ultrasonic anemometer/wind vane is a higher priority.
The pots in the hobby servos I've taken apart are free turning. The pots depend on the stop tab on the gearing output shaft. You might get an inexpensive pot and see if it can be disassembled to remove the internal stops. In the future I'm going to remove the stop tab on a hobby servo and see how it controls.