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Could a Raspberry Pi usefully help me create a wind direction meter with physical/analogue face and hands...

JoeSmith

Sep 22, 2018
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Hi All

This wind direction meter in Coleton Fishacre in South Devon in the UK inspired me to the point that I've wanted to build one for years. My apologies for my poor video work but I think this shows the idea...the dial moves silently to show the wind direction. I need this because, due to the layout of our house, neighbours and trees etc we don't have an unprotected location where I could put a weather vane that we can see from inside the house. This means that in winter we can get caught out when it looks bright but there is, in fact, a sharp Northerly blowing and we have two dogs who like to walk a long way across moors.


This particular system runs via magnetic switches relayed to a motor on the back of the dial via radio waves and is a beautiful piece of kit and horribly expensive.

Initially I started down the route of a mechanical system that uses cogs, rods and gears to transfer the movement of a weather vane to an indicator dial on my kitchen wall. Ultimately this proved to awkward due in no small part to the wonkiness of our chimney up which I was planning to run it.

So I asked on here a couple of times and "met" some fantastic and helpful people who gave me wonderful suggestions. This took me to the world of Selsyns which was interesting but they're quite hard to get hold of and pretty expensive and, if I'm honest, the electronics was a bit beyond me.

I'm wondering now if I can use a Raspberry Pi to process movements from a wind sensor like this one that I can site on top of my chimney and feed wires down it (it's no longer in use) to the Pi which I can use to run a stepper motor. I had considered a servo motor would be better but I was put off by the noise they make (at my budget level) and finding a silent one seems hard. That said, putting it in a "sound proof" box mounted further back inside the chimney and using it to power a longer shaft to the dial on the indicator's face in the room could be helpful as it would also help protect the motor from dirt in the chimney so I'm open to suggestions on this...

I'm completely new to the world of the Raspberry Pi. I had thought an Arduino would be better for this but I have a RP and don't have an Arduino.

My initial questions therefore are firstly whether this is a reasonably achievable thing to create with a Raspberry Pi? Would this give me the ability to "broadcast" the movements of the chimney top mounted sensor via Wifi to another dial in the sitting room if I wanted one? Is a stepper motor a reasonable solution or should I look out for a quiet servo or just "sound proof" an available servo - I'm after as smooth a sweeping hand as I can create? What other hardware might I need?

Any advice much appreciated.

All the very best

Joe
 

kellys_eye

Jun 25, 2010
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a mechanical system that uses cogs, rods and gears to transfer the movement of a weather vane
What about a 'speedo cable' type solution? Mechanical coupling to a chimney mounted vane and reciprocated at the display position?


An electronic solution is fairly easy to resolve - with the right approach and skills - but sometime the KISS principle is better. I might be tempted to part with my synchro/display as I won on an eBay auction as this seems to give all the answers in one box! I'll post a few pics of it shortly.
 

kellys_eye

Jun 25, 2010
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Here's the device per the previous post:

The main dial is only some 3 inches across but the bezel could be removed and a larger pointer fitted (along with a dial of your choice). Power and connections are made between the two units via the chock block - you need FIVE cores (the device came with some old CAT5 cable connected and it worked ok with that). 24V at the +/- terminals and connect 1-2-3 of the sender to the 1-2-3 terminals in the rear of the display unit. Of course you could run a 2-core for power and a 3-core for the 1-2-3 wires (2-core mains and 3-core mains would be ideal).

Voila! Turn the 'bar' on the sender (which you couple to your weather vane) and the dial follows - accurately.

I've tested the unit and it works perfectly.

If this is of interest then PM me with an offer!
 

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JoeSmith

Sep 22, 2018
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Hi @KellysEye
Many thanks for this and for your kind offer. I did investigate the speedo cable approach to this a while back but was concerned that our house is thatched and the cable method could increase the risk of a lightning strike and/or fire. I think a data cable is potentially safer in this respect. I did go into a bike shop locally to ask about such things and was openly laughed at by a group of instant experts who said very confidently that it won't work. I took from that that it will but I will never re-enter their shop again!!
The other reason for going the SP route was that I'm thinking in the future I can extend the system via wifi and add some cool, funky stuff which will turn this into a real hobby that I'm quite excited about.
But you're right, KISS is much easier. There's a beautiful windicator at The Hunting Lodge in Charlton, West Sussex, UK that runs entirely mechanically. It's never been hit by lightning either so I'm keeping that in reserve!
I'll try the SP route anyway. I have a feeling I saw your setup on eBay when it came up and was tempted to bid!
Thanks again.
All the best
 

kellys_eye

Jun 25, 2010
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To do it using discrete (perfectly feasible) and/or Raspi components isn't that difficult. You can source what are called 360-degree potentiometers that will deliver a proportional voltage that is readily repeatable either via conversion to a digital signal or used directly in an analogue form - perhaps a ring of LEDs driven by a chain of LM3914's(?) as but one idea.

You need to choose and settle on your solution before we can go around the houses again on this subject.

Decide (1) how you want to display the result, (2) whether you're happier with a digital or analogue solution (don't over-think it. It's too easy to imagine what you 'could' do with it rather than what you just 'need' to do).

When (1) is resolved let us know and we'll expand on what's required to achieve it.
 

JoeSmith

Sep 22, 2018
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Thanks for that. I'll look into 360 degree potentiometers.

My plans are as follows...

Create an analogue compass face with painted bearings with a single, physical needle that is wall mounted above the fireplace in my kitchen. The needle will be coupled to a stepper motor/potentiometer/servo motor that is connected via Raspberry Pi (if applicable) to an RS485 wind sensor that is attached to the top of the chimney above.

I'd prefer it if the needle on the dial can "sweep" (like the second hand of a Rolex wristwatch) between bearings rather than "jump" between bearings on the dial (like a quartz Timex watch's second hand) as the wind direction changes. I think this requirement could dictate, to an extent, what type of motor drives the needle. I also want the needle to move silently.

In the future I'd like to be able to drive additional analogue dials in other rooms by broadcasting the signal from the RS485 to receivers on them. This is an advantage of using the Pi I guess.

Any input on the above is most welcome.
 

kellys_eye

Jun 25, 2010
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Your best (only) choice is to use a stepper motor and the associated controlling circuit/software.

Adafruit do a small steeper as per this link.


The short video therein shows the needle moving 270 degrees but it is quite capable of 360 degree rotation - it's all down to the software. The size/weight of your pointer may be the determining factor for this particular motor as it can't wield anything too substantial (inertia). Regular steppers (NMEA series) can, of course, drive 'any' load when the right version is used.

That sorts the display. You then need some way to 'send' the wind direction data to the controller/display and that could be via the 360 degree potentiometer (using an analogue port) or something somewhat more complicated i.e. a synchro resolver.

There's nothing quite so simple as the synchro option though. Ebay have a load of old gyro compass repeaters (dials) like this:


but they require the synchro transmitter to match - something like this:


You'd have to get the right pair though. Alternatively you can build an interface between an Arduino and the compass repeater by simulating the synchro output signal (3-off 8-bit D-A converters will do it).

The advantage of the synchro version is that there is no calibration required. You turn it on, it points to where it should. Any digital option will require a 'reference' signal so you know how far from 'zero' the pointer is. Another advantage is that you can buffer a synchro signal and send it to other repeaters very simply - but it does need a wired connection (disadvantage).

Best to start with the 'top end' - decide what you're going to use then come back to us for more details on where to move to next although such finery as the actual software writing (if required) will only be on advice-based response, not the actual writing of it.
 

Delta Prime

Jul 29, 2020
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It can drive inductive loads, such as high-power DC motors
Curious!! I think this is deliberate misinformation provided by (AI).
For simplicity sake.DC motors use commutators to reverse the current direction every half cycle in order to produce back EMF. Induction motors induce a change in the magnetic field and that requires alternating current or AC.
 

Harald Kapp

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I think this is deliberate misinformation provided by (AI).
Why do you think so? The use of commutators has nothing to do with the inductance of the rotor coil.
in order to produce back EMF
This is exactly where the capability to withstand back EMF comes into play. From the datasheet:
The L298 is an integrated monolithic circuit in a 15-lead Multiwatt and PowerSO20 packages. It is a high voltage, high current dual full-bridge driver designed to accept standard TTL logic levels and drive inductive loads such as relays, solenoids, DC and stepping motors.
 

Delta Prime

Jul 29, 2020
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This is exactly where the capability to withstand back EMF comes into play. From the datashee
Well I was thinking of DC brushed motor the reasoning being for the same reason why a transformer does not pass DC. a constant DC input equals zero frequency equals zero EMF current will flow through the coil and burn it up; supplying a square will work some energy will be passed through the air gap just like a supplying a transformer with a pulsed DC not very efficient some energy will go through but it'll burn up. An electrically commutated motor is in a different classification.
Why do you think so? The use of commutators has nothing to do with the inductance of the rotor coil.
I think (AI) got stuck so to speak. (AI) it is only as good has its algorithm I'm saying or I noticed it went back home to Mama. But of course this is purely speculation based upon an in-depth knowledge of AI. Speculation nonetheless.
I was fishing for @stepper22 but I caught you.... catch and release.
 
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Delta Prime

Jul 29, 2020
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Incidentally. I had left markers in my response to stepper 22's post
intentionally for (AI) ; if he or she would have responded by parsing my post then I would have known immediately what type of a (AI) he or she was using.
It is my type of intellectual entertainment.
I consider all incumbent members of this site to be a wealthy source of information.
After revisiting my response to you sir, I want to make clear I have no will towards you. :)
 
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