Need help interfacing weather vane
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I found a nice wind speed / wind direction unit at the Boeing Surplus
store. After messing with it, I determined that the wind speed unit
is a small AC alternator.
The weather vane is a little more interesting having a percision
wire wound pot. The pointer has TWO wipers on it that travel
across the pot and this connection is brought out. Picture a round
wire wound pot with a connection at each end, and the wiper
comes out as the third connection. The whole pot reads 154 ohms with
wiper removed using a decent fluke meter. Reading between the wiper
and each end of the pot, you get two resistances that will add up to
154. Example 153,1 or 100,54 ... depending on the direction.
I think that this design allows one to cover the dead spot in the pot.
WHAT I NEED HELP WITH IS: What is the most direct way to interface
this device to the Stamp?
I was thinking about sending a reference voltage out to the wiper and
then reading the voltages coming from either end of the pot via two
channels of an A/D. But there might be a much easier way to interface
this unit??
As for the wind speed, I was thinking one could count the cross overs
of the AC. If someone has a good suggestion on this as well, I'd
appreciate hearing from you.
store. After messing with it, I determined that the wind speed unit
is a small AC alternator.
The weather vane is a little more interesting having a percision
wire wound pot. The pointer has TWO wipers on it that travel
across the pot and this connection is brought out. Picture a round
wire wound pot with a connection at each end, and the wiper
comes out as the third connection. The whole pot reads 154 ohms with
wiper removed using a decent fluke meter. Reading between the wiper
and each end of the pot, you get two resistances that will add up to
154. Example 153,1 or 100,54 ... depending on the direction.
I think that this design allows one to cover the dead spot in the pot.
WHAT I NEED HELP WITH IS: What is the most direct way to interface
this device to the Stamp?
I was thinking about sending a reference voltage out to the wiper and
then reading the voltages coming from either end of the pot via two
channels of an A/D. But there might be a much easier way to interface
this unit??
As for the wind speed, I was thinking one could count the cross overs
of the AC. If someone has a good suggestion on this as well, I'd
appreciate hearing from you.
Comments
http://www.weatherstamp.com
Matt has a pdf file there with code for reading it. BASICally, if
one wiper is near its dead band, the software switches to use the
reading from the other wiper and adds the appropriate offset.
The output from the AC generator can be run through an LM2917-8
tachometer chip. Without filtering the LM2917 gives digital 0-1
pulses for counting, or with filtering, it gives an analog output
proportional to windspeed for an ADC.
-- best regards
Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com/OWL2face.htm <-- more anemometer info
mailto:tracy@e...
gbrecke@y... wrote:
>I found a nice wind speed / wind direction unit at the Boeing Surplus
>store. After messing with it, I determined that the wind speed unit
>is a small AC alternator.
>
>The weather vane is a little more interesting having a percision
>wire wound pot. The pointer has TWO wipers on it that travel
>across the pot and this connection is brought out. Picture a round
>wire wound pot with a connection at each end, and the wiper
>comes out as the third connection. The whole pot reads 154 ohms with
>wiper removed using a decent fluke meter. Reading between the wiper
>and each end of the pot, you get two resistances that will add up to
>154. Example 153,1 or 100,54 ... depending on the direction.
>
>I think that this design allows one to cover the dead spot in the pot.
>
>WHAT I NEED HELP WITH IS: What is the most direct way to interface
>this device to the Stamp?
>
>I was thinking about sending a reference voltage out to the wiper and
>then reading the voltages coming from either end of the pot via two
>channels of an A/D. But there might be a much easier way to interface
>this unit??
>
>As for the wind speed, I was thinking one could count the cross overs
>of the AC. If someone has a good suggestion on this as well, I'd
>appreciate hearing from you.