Since Xmas I’ve been busy hacking away at things. I tried to install Ubuntu on my Mac Mini and ended up screwing up the EFI pretty royally to the point where I had to remove rEFInd (which didn’t work well anyway), repartition the drive, reinstall OSX, update, and fix things like a randomly disappearing RecoveryHD partition and OSX installing an old version of Safari 5.1 instead of the current 6.1, and then never updating it. The fix for that was to delete it and then Software Update can see the new one is available:

My weather station is still going strong after three days on the Alkaline batteries. Now I’ve got quite a bit of data, I thought I’d better do something more useful that just tweet it.

The problem was I was only storing the current hour’s weather data, so I had to import my data back from Twitter! Now whilst you can get a CSV archive of your tweets, you can only get it about once a month which is stupid. So I ended up using some grep/sed tricks on the web page to get my data, and then wrote an importer to remove the prettifying and get it back into the original data format. That meant that I had a starting point for my database so I didn’t waste three days’ worth of data. I also found that my timestamps weren’t being stored as datetime objects, so had to fix that too.

I found that my weather station only lasted for about 7 hours on 2xAA batteries last night. The culprit could be the boost regulator, but before I investigate that I’ve reworked my Arduino code and moved away from manually tinkering with the avr/power.h stuff to using JeeLib. Its greatly simplified my code too. I removed the code that was measuring the voltage as that always returned 3.37v from the boost, so a bit pointless, plus it kept the ADC awake draining power.

I’ve just received my Pololu U1V10F3 3.3v boost converter and 2xAA battery pack from HobbyTronics and it took no time to convert the veroboard from a coincell to the boost+batteries, I now have a stable 3.3v (from 3.31-3.37 recorded so far) and the sensors are working much better now.

I updated my code to store the voltage so that I know when the battery is dead and the boost can’t work, that meant moving the dewpoint calculation to the Raspberry Pi as it made my RF24 packet too large otherwise.

I’ve been thinking about a way to monitor the battery supply voltage of my weather station remote node, as I was thinking of buying some LiFePO4 or LiPo batteries which don’t cope well with over-discharging.

Its all a bit moot as in the end I decided to stick with regular NiMH/NiCd rechargeable batteries and get some of Pololu’s new miniature boost regulators in 3.3v and 5.0v varieties. They’re pretty nifty as not only can they make 3.3/5.0v from as little as 0.5v, but they can also automatically regulate down from 5.5v 1.2A, so not only can you run off of two AA batteries, you could also run off of four, all from about 1cm2!