Weather Station Ideas

[skybadger]

You only need one adc for reading the voltages acRoss the bearing resistor network  according to one supplier. (But not usi g  the Circuit above). The adc doesn't have to be the native one either, I use one on the i2c bus for that and the bme device. 

The anemometer only needs one Reed or hall or other sensor which means one pin, but if that is not the way you want to arrange things there are other ways, two digital pins for an encoder or optoswitch for example. 

[Gina]

Yes, I have a circuit diagram for using 8 reed switches and a resistor network giving a single analogue signal to feed to the ESP or whatever.  Trouble is the resistors are unusual values.  OK, these could probably be produced by using preferred values is series or parallel but it's a lot of resistors whereas 8 wires from one side of the reed switches could go to the ESP with the other ends connected to Gnd - much simpler.  OTOH the 1-wire circuit above with 4 analog signals could be fed to the ADC inputs of an ESP32 giving another (more complicated) possibility.

[skybadger]

Sure, but it's up to you to find resistor values that are equally spaced from a standard value sec. As lo g as you can distinguish between them it doesn't matter. 

 

[Gina]

Here is a resistor network using preferred values that gives a voltage proportional to angle in 16 steps.  Except that it has a serious fault!!  I think.

[Gina]

Labelling the reed switches 1 to 8 from the bottom upwards...  Assigning v to the voltage across each of the series resistors - 1/7th of 3.3v

1. 1 - 0v
2. 1&2 - 0.5v
3. 2 - 1v
4. 2&3 - 1.5v
5. 3 - 2v
6. 3&4 - 2.5v
7. 4 - 3v
8. 4&5 - 3.5v
9. 5 - 4v
10. 5&6 - 4.5v
11. 6 - 5v
12. 6&7 - 5.5v
13. 7 - 6v
14. 7&8 - 6.5v
15. 8 - 7v

Then we would have 16. 8&1 - 7/2 = 3.5v which is the same as 8. with 4&5.   So no difference between positions 8 and 16.  I though I'd cracked it but not so!!

Edited June 30, 2020 by Gina

[Gina]

The reed switches have arrived and I've checked their operation.  They're very sensitive one of my little 3mm cube magnets will operate one at 5 or 6mm.

[Gina]

I'm wondering if I can produce a resistor network with standard resistor values viz. 1, 2.2, 4.7, 10, 22, 47.

Suppose we make inbetween values by adding another resistor in series, like this :-

1. 1
2. 1 + 0.22
3. 1 + 0.47 = 1.47
4. 2.2 + 0.47 = 2.67
5. 2.2 +1 = 3.2
6. 4.7
7. 4.7 + 1 = 5.7
8. 4.7 + 2.2 = 6.9

Then between those 8 values we have adjacent resistance values in parallel giving in ohms :-

1. 1000
2. 549.54
3. 1000 + 220 = 1220
4. 666.7
5. 1000 +.470 = 1470
6. 948
7. 2200 + 047 = 2670
8. 1456
9. 2200 +1000 = 3200
10. 1904
11. 4700
12. 2576
13. 4700 + 1000 = 5700
14. 3121
15. 4700 + 2200 = 6900
16. 873

Putting these in numerical gives

1. 549
2. 666.7
3. 873
4. 948
5. 1000
6. 1220
7. 1456
8. 1470
9. 1904
10. 2576
11. 2670
12. 3121
13. 3200
14. 4700
15. 5700
16. 6900

Some of these are quite close together.  Maybe some primary values (8) could be adjusted to separate the secondary values (16) better.  The resistance values would translate to voltage if the array were fed with a constant current but that would make the lower values very close together.  Better would be to feed from a constant voltage through a resistor, then the lower switches would result in a higher current and tend to spread the lower values.

All this is getting very complicated and probably not worth the trouble!

[Gina]

Nuts to that!! 🤣  Just a bit of fun anyway - may play again later.

I'm sure the best option is the ESP32 and either 8 digital or 4 analog inputs and the 1-wire circuit.

[JamesF]

40 minutes ago, Gina said:

All this is getting very complicated and probably not worth the trouble!

Especially if you think a single mux chip would be too much

James

[Gina]

I have a MUX chip it's an ESP32! 🤣  I like the 1-wire circuit but replacing the 1-wire with ESP32 which does everything.

[Gina]

Pretty much decided to go with the reed switches for a couple of reasons.  I was going to use a cylindrical arrangement but magnet and reed switches need to be something like 8-10mm apart so I think the traditional radial arrangement is going to be better, may be easier to implement too.  Makes it easier to adjust the distance between magnets and reed switches to get the right overlap in operation.

[7170]

You can see the 8 standard resistor values used in this popular model that lots of cheap weather stations use:

Wind Vane Datasheet

"Only" needs 8 resistors, 8 reed switchers and one analogue input.

[Gina]

But several of those resistors aren't preferred values.  No problem if manufacturing the resistors but we amateurs have to use the resistors we can get.

Edited June 30, 2020 by Gina

[7170]

27 minutes ago, Gina said:

But several of those resistors aren't preferred values.  No problem if manufacturing the resistors but we amateurs have to use the resistors we can get.

64.9kR isn't in stock everywhere but you can get on eBay/mouser (I admit a bit of a faff). The rest should be easy to get hold of online (Bitsbox for example).

Edit- in fact from Bitsbox you could use 1% 62kR+1.8kR+1.1kR and get all the others as single resistors from there.

Edited June 30, 2020 by 7170

[Gina]

16K isn't either but maybe 15K is near enough.  OTOH some of the voltage values are very close!

[7170]

16kR is a standard E28 resistor.

Yes some are rather close but lots of people connect up that wind vane to  arduinos with success. There must be a method in the madness somewhere 😀.

Do you have a laser printer, maybe a diode measuring an led shining through a circular piece of laser OHP film with varying density around it? Similar idea to a variable density optical soundtrack on old 16/35mm film prints.

[jiberjaber]

I wouldn't worry about the accuracy of the resistor values, just bang in the required number of 10K and 1K and then use a scale function to map the minimum and max ADV measurement to 0 and 360 degrees. 

eg: 

float winddirstate = map(analogRead(WD_Pin),0,1023,0,360); 

If that doesn't give you the right direction (due to resistor tolerance vrs read switch resolution) then empirically measure the ADC value for the locations you are interested in and use the values to discern the wind direction reading?

The Davis wind direction just uses a potentiometer without end stops - I figure if it's good enough for them, then might be worth consideration if you are now at the point of using the ADC

[jiberjaber]

The 360 deg pots are not cheap though, £38 for a 3.8mm dia spindle version. Not sure which one is in the Davis unit however here's one (£10!) which is rated for 2 million revs and has an IP rating too...  (datasheet in the link) - might be a cheaper version on one of the far east sites - though I think if this is going on the end of a pole and inaccessible, I'd perhaps opt for paying a bit for reliability

https://www.mouser.co.uk/ProductDetail/CTS-Electronic-Components/282T33L502A26C2?qs=sGAEpiMZZMukHu%2BjC5l7YQKnx7lgrENNMXOfQ6BaUek%3D

[Gina]

8 hours ago, 7170 said:

16kR is a standard E28 resistor.

Yes some are rather close but lots of people connect up that wind vane to  arduinos with success. There must be a method in the madness somewhere 😀.

Do you have a laser printer, maybe a diode measuring an led shining through a circular piece of laser OHP film with varying density around it? Similar idea to a variable density optical soundtrack on old 16/35mm film prints.

No, I don't have a laser printer.

[Gina]

One thing I've found with the reed switches is they have considerable hysteresis (distance between closing and opening).

I might yet go back to optical sensing.

Edited July 1, 2020 by Gina

[Gina]

One thing I've found in the past is problems with the miniature ball bearings with damp causing corrosion.  I'm wondering about using PTFE and SS plain bearings.

Edited July 1, 2020 by Gina

[7170]

1 hour ago, Gina said:

One thing I've found in the past is problems with the miniature ball bearings with damp causing corrosion.  I'm wondering about using PTFE and SS plain bearings.

Agreed, ones I have seen usually use plastic, brass or SS parts on the spindles.  Also avoid any oil/grease too as that can end up just being a receptacle for dust/gunk over time, making it harder to spin.

[Gina]

I'm wondering whether to put the 5m mast in a place where I can get at it relatively easily rather than where the wind would be clearest.  ATM I have no weather station so almost anywhere would be better than nothing.  I also need to consider that I'm not getting any younger.

[pete_l]

Quote

a place where I can get at it relatively easily rather than where the wind would be clearest

Since we're talking in an astronomy forum, it seems to me that the best place for an anemometer would be close to your telescopes. That way you can assess the impact that wind has on them and on your imaging.
With experience you could then know when there were good conditions for viewing, or when it was too windy for the telescope to remain stable.

[Gina]

I agree with that but it mustn't interfere with imaging - ie. be in the FoV available from the mount.