Home Brew Weather Station (Part 4)

The small OLED display arrived and after an hour or so getting it to work I hit another problem. The Arduino Uno didn't have enough memory space to store all the new library instructions. Fortunately I had a spare Arduino Mega which has oodles of memory space so transferred everything to that. The sketch (program for the Arduino) now consists of nearly 200 lines of instructions which compile to about 20K (20,000) bytes of code with nearly 2K of additional space needed for storing information.

This is the OLED display:



It consists of an array with 128 dots across by 64 dots down which can be made to glow like light emitting diodes. Unlike TFT screens it has no need for a back light so the background stays a deep black. Even though the display measures a fraction less than an inch it is very easy to read the lettering.

The thin wavy line seems to have been a foreign body on the display as it cleaned off this morning. My only concern is the temperature the display reaches. I picked it up after it had been on for a few hours and nearly burnt my finger. An IR thermometer showed part of the back had reached 40C. It does have a working range from -30C to +80C so maybe that is normal.

Monday Mystery - Guess What

Congratulations and the virtual Midmarsh Gold Star to TexWisGirl, Wilma, Ragged Robin and Adrian for identifying last week's cloud formation. Acutally called mammatus or mammatocumulus. They can occur when the rising moisture and ice crystals in the cloud become too heavy and start to descend making large bumps below the main cloud. These can be a mile across. It is usually  associated with thunder / storm clouds.





The formation can be very short lived so I was really pleased I popped outside at just the right moment to be able to record the phenomenon.

Back to a closer view of something for this week's mystery photo.
Guess What:


Please leave any guesses in the comments.
They will be revealed, along with the answer, next Monday.
No prizes, just for fun and maybe a virtual Midmarsh Gold or Silver Star.

Clouds + Home Brew Weather Station (Part 3)

Interesting (to me anyway) mix of clouds spotted yesterday:





Today has been grey all day. As the wind is now coming from the East it has felt bitterly cold.


The home brew weather station is still evolving. I spotted a barometric pressure sensor suitable for use with the Arduino and other similar computers. After a hassle with the Arduino IDE not liking the library for it I had to update to the latest version of the IDE (used on the computer for writing the program / instructions / sketch). So far to check the sensor works I have it sending its readings back to the computer for display. As always I found out how to program it by searching the internet. What would I do without it?



The sensor is tiny, slightly smaller than my thumb nail and a steal at £2.56 (about $3.70). Next will be to add an OLED type display to show the pressure and it will also enable me to show the humidity readings. That's the theory anyway.

There was a strange glitch with the 7 segment displays. The top one kept going blank. Still not sure why. The driver chip can send the display to sleep to save power so that may have been happening at various intervals. It shouldn't as I send a command to wake it up at the start of the program. Then it is supposed to stay awake unless told to sleep. Anyway I added a further wake up instruction every time the display is updated. It's been running on a soak test for nine hours and so far it has displayed everything properly so that will have to do for a cure.

Home Brew Weather Station (Part 2)

I had a change of mind with the display. For me not only the immediate temperature is of interest but so are the maximum and minimum temperatures.

First thought. With a bit of extra coding and rearranging the display I came up with:



Top left, immediate temperature.  Top right immediate percentage relative humidity.
Bottom left, maximum temperature, Bottom right, rainfall in mm.



Switched so the bottom left shows minimum temperature.
I put the sensor in the top of a freezer to check it showed negative temperatures OK.

Further thought. Do away with the humidity reading:



Now I have:
Top left, immediate temperature, Top right, total rainfall in mm
Bottom left, maximum temperature. Bottom right, minimum temperature.

Finally:


I am quite pleased with the final layout. The whole thing draws less than 80mA.
Once cased the unit will have buttons to reset max / min temperature and rainfall. On my old home brew rain gauge I reset the count at the beginning of each month and I would probably want to reset max / min temp daily.

Wordless Wednesday

18th January 2007

Home Brew Weather Station (Part 1)

I've been working on my home brew weather station based around an Arduino Uno R3. It will measure and display outside temperature in Celsius, percentage relative humidity and rainfall in millimetres.

Temperature and humidity are detected with a DHT22 module:


Rainfall will be measured with a tipping bucket:


Inside the box is the tipping bucket so designed that water entering fills the high side of the bucket. That causes the seasaw to flip emptying that side and presenting the other side to collect more water:


The number of flips is detected with a magnet and a reed switch. This bucket had failed, as they often do after a lot of use. It would appear the reed switch, which consists of two short metal bars which bend and close the contact when a magnet is close, becomes weak and the contact is not made or the contacts become corroded somehow and again stop the contact being made.

This is the original reed switch in place with a replacement next to it:


Originally the reed switch was placed so it made contact briefly as the magnet passed it but that was no use for what I wanted so I offset the new one so it closes when the bucket is in one position and opens when the seasaw tips over:


Here you can see the positions of the reed switch and the magnet when closed:


and when open:


Finally the display which uses two 8 digit 7 segment LED displays:


Top left Temperature in Celsius, top right relative percentage humidity.
Bottom row rainfall in millimetres. The programming for the rainfall got a little complicated as the rain gauge apparently makes 3 tips for each mm of rainfall but I got there in the end.

Next job is to box the workings and wire it all up.

Monday Mystery - Guess What

OK. Last week's mystery photo brought out some interesting guesses. It could well have been the top of a thermos flask but in fact Adrian hit the nail on the head ... it was a close view of a light / lamp / bulb socket. Wilma also mentioned light socket but wondered where the contacts were. I kept them out of view! It is  heatproof ceramic socket for Edison screw bulbs. Anyway they both deserve my congratulations and the virtual Midmarsh Gold Star.

   

I did have another close shot for this week but changed my mind at the last minute. As I was putting my soldering iron away in the shed I noticed a cloud formation I have seen many times in other peoples' photos but have never seen myself, until today. Your task, if you wish to take it, is  to identify the name of this formation of clouds (yes I do already know the answer - I hope).

Guess What:


Please leave any guesses in the comments.
They will be revealed, along with the answer, next Monday.
No prizes except maybe a virtual Midmarsh Gold or Silver Star.