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My little weather station is run on a Nano and has the anemometer and the temp/humidity sensor. A smoke detector is on the way because I live where wildfire is a big concern.

I would like to build a simple weather vane without spending a lot to buy the commercial solutions. Rotary potentiometers have dead spots and using a bunch of hall effect sensors would use up too many digital inputs to be useful, afaik.

Question: How can I build a simple direction sensor?

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    There are two-axis analog hall sensors that detect the orientation of a magnet, but they cost a bit more. You could probably make yourself a low resolution absolute optical encoder with hand tools or a 3d printer. – Chris Stratton Oct 26 '16 at 5:16
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    Use two pots with the dead-spots at opposite ends. – Gerben Oct 26 '16 at 8:40
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    Not sure but I think you should be able to use a magnetometer (compass). 5US on Amazon.com could afford you something good enough. amazon.com/HiLetgo-HMC5883L-Electronic-Compass-Magnetic/dp/… – Dat Ha Oct 26 '16 at 11:45
  • Thank you for your pointer. Here is the one I just ordered: amazon.com/gp/product/B00SDTFI1Q/… – SDsolar Oct 27 '16 at 23:35
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Its a long time since I looked at this and the details are a bit misty, so sorry for the inaccuracies, but I'm sure people will correct them for me :)

I originally brought one of these http://www.maplin.co.uk/p/maplin-replacement-wind-direction-sensor-for-n96fyn96gy-n81nf and then decided to take it to bits, like you do.

The vane spins a magnet around and this triggers 1 of 8 reed switches as it passes around. The read switch is connected to VCC and a resistor and the resistors feed into a common wire back to the microprocessor. The 8 resistors all have different values, so the result is a differing output voltage depending on which reed switch has been triggered.

So what you need is:

  • A magnet
  • A number of read switches positioned far enough apart so only one is triggered at a time
  • A number of different resistors

Supply 5V from you Nano and read the result on an analogue pin, then come up with a calibration table to work out the direction.

I hope that makes sense. (Sorry I can't draw you a circuit diagram)

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Another option (similar to reed switches) is to do it optically.

The vane is on an axle. The axle has a disc attached to it. The disc has a small notch out of the edge.

Positioned around the edge are a whole series of photo-interrupters. The disc spins between the infra-red beams and the notch allows only one of them to pass light at a time.

Make the notch the right size so that as one interrupter turns off the next one turns on - you need one on all the time. You could over-compensate slightly so that on occasion two adjacent interrupters are on at once, in which case you can say it's between the two.

A similar system is to use a disc with a series of special slots cut in it (see Gray Code) which allow light to pass through onto a line of photodiodes. In different rotations different combinations of photodiodes are on, and that gives you your direction.

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    The Arduino has plenty of pins (unless you're using lots and lots of them already). Think KEYPAD. – Majenko Oct 27 '16 at 21:03
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I decided to go with 4 reed sensors. With experimentation I found I can successfully detect 8 distinct directions using 4 reed switches since the rare-earth magnet will switch two on at once when it is in between.

Thank you all for your answers. Upvotes for everyone for the discussion.

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