richard

Aspirated air temperature sensor for a Polytunnel

In the UK air temperature is normally measured in a passively cooled Stevenson screen. The louvred design of the screen allows air to flow around the thermometer. The trouble with a polytunnel is there is no wind at all, as a result the sun heats the sensor up and without airflow you don’t know by how much.

By running a computer fan driven off a solar panel I can move enough air past the sensor to exchange the heated air from the sun shining on the sensor. For the sensor I use the standard Chinese supplied DS18B20 encapsulated in a stainless steel tube

Dallas DS18B20 epoxied in a stainless tube housing, from a Chinese Ebay supplier

The sensor is housed in a 6cm piece of white plastic waste pipe

sensor mounter in centre of white waste pipe — sensor mounted in centre of white waste pipe

The fan is mounted at the top of the pipe, designed to pull in air from below; this way the sensor is not heated by air passing the fan motor, and the airflow works with the natural tendency of warm air to rise. I’ve tried to keep the airflow as unimpeded as possible.

side view - the flange for the fan is made from a piece of wood glued to the pipe — side view – the flange for the fan is made from a piece of wood glued to the pipe

Looking at the results there is a difference of a few degrees

the difference opens up a few degrees at high temperature

between the aspirated sensor and another sensor mounted on the outside of the plastic tube. They track at low temperatures but not when the sun is shining – the difference here is about 6 degrees, even in March, before the vernal equinox. It is remarkable just how much the air temperature swings – 27 degrees on a couple of days which still have hazy sun.

Weatherproofing the sensor is easier in a polytunnel because as well as the wind not blowing, it also doesn’t rain. I can use a cheaper indoor solar panel, the one I used is a 12V 1.5W unit, Maplin L58BF bought on sale for about £6, not the £20 they seem to be charging for it. even £6 is a little dear! I extracted the flashing blue LED and series diode to maximise the power available to the motor. This also charges the battery of the temperature sensor dual unit, which reports back to the collecting station using Ciseco’s XRF every 10 minutes.

The computer fan was a 12V brushless unit but I run it at about 7V, we’re not after blowing a gale through the tube. It will start at 5V. The Zener is there to limit overcharging of the 4.8V NiMH battery pack in the electronics to about 4mA. It only reports every 10mins so this is enough. The 1N4148 diode stops the battery discharging back through the fan and solar panel in the night. I should really measure what the leakage current of that Zener is 😉

I used a PIC 16F628A driving a Ciseco XRF to send the temperature data from two sensors back. Nowadays I would use the Ciseco RFu which includes an Arduino and low-power standby mods to make this cheaper.

Other implementations

This is a nice weatherproof design – I can’t work out if I missed a trick with using just one plastic tube rather than a coaxial design. Lots more ideas here.

Postscript (July 20 2015)

This rig works reasonably well; if power were available I’d run the fan all the time in daylight for a more rigorous result on summer cloudy days. The biggest problem in a polytunnel is that they are shockingly dusty places, and you have to sponge the dust of off the solar panel every month or so.

The Texas LP2950 oscillates as an adjustable regulator

Nowhere in the datasheet does Texas tell you “hey use this fixed regulator as an adjustable”. However, I’m used to being being able to do that with the venerable 78XX series – indeed Texas tell you that you can do that with the 78L05 datasheet in Fig 14.

Adjustable 78l05. bear in mind the shocking Iq of 3mA that'll stand you up an extra 3V if resistor R2 is 1k, keep 'em low... — Adjustable 78l05. Bear in mind the shocking Iq of 3mA that’ll stand you up an extra 3V if resistor R2 is 1k, keep ’em low…

Given that there’s an adjustable variant of the LP2950 that appears on the same datasheet (the LP2951) I laid out a PCB and being the lazy sort I am I assumed that since I was using a load of these parts in their 3.3V KY5033 variant, where I wanted an 8V stabilised voltage for an audio mic amp sourced off a 12V supply I can simply do the LM317 trick, drop in a couple of resistors from the output to ground and the ground pin to real ground, job done.

For this I made R1 6k8 and R2 10k.I expected an output voltage of 3.3+3.3/6800*10,000=8.2V or near enough. I screwed up labelling the o/p 10V, mistakes happen…

What does that look like then?

Oy vey, about 4V of massive oscillation (I’m using 10x probes). At least it’s centred on the right value-ish. Let’s take that output capacitor out

Looking good, only 1V of oscillation, now at 370kHz or thereabouts.

So if you come here from Google wanting to know why the LP2950 doesn’t work as an adjustable reg, now you know. There is a tiny clue in the datasheet in the ground current variation

which varies by two orders of magnitude with a load current variation of 1000. This will be impressed upon R2, varying the target voltage – as more current charges the capacitor the target voltage will rise, then ease off as it is charged, making a handy relaxation oscillator.

There’s another clue that the output cap can give interesting results in this line

which actually specifies a ESR range, rather than less is better

No criticism of Texas’ product implied – these are great little fixed voltage regs with a low quiescent current and are my goto device for running 3.3V devices off a 5V rail because of that superb dropout voltage of 600mV max, across the entire range of load current and -40 to 125°C which is easily in spec off a 4.75V min 78L05. It’s just one less thing to worry about. Im future I won’t be a doofus and try and use one where a LM317L is called for 😉

Curlew at Melton Riverside

I love curlews – they may be common as muck round these parts but the beautiful plumage, strange down curved bill and haunting bubbling call make them special.

The little nature reserve at Melton has a free car park and you can get a view of the riverside mudflats near Wilford Bridge

It’s a pleasant walk along the river into Woodbridge, there is another small level crossing to get into the town. On the other side to Wilford Bridge going north there is a footpath toward Broweswell reedbeds and it’s worth a look at the birds on the riverside there too

[osm_map lat=”52.102″ lon=”1.335″ zoom=”15″ width=”100%” height=”450″ marker=”52.10401,1.33903″ marker_name=”wpttemp-green.png” type=”Mapnik”]

Trimley Marshes Nature Reserve

Trimley Marshes - next to the massive container port of Felixstowe — Trimley Marshes – next to the massive container port of Felixstowe

SWT reserve Trimley Marshes is a long walk from the car park – about 2 miles to the hides. That’s good because it means you can sometimes have the place to yourself 🙂 On a bright winter day like today it is the Suffolk coast at it’s best, despite the surreal juxtaposition of the low rumbling sounds of the container port with the calls of the birds. The noise of the container port fades with distance. The port is behind you when looking at the birds, the sound wasn’t obtrusive from the second hide onwards.

tranquil view oof the reedbeds at Trimley — tranquil view of the reedbeds at Trimley

1502_brents_IMG_2567 — Brent Geese arriving

I was treated to some lovely views of winter ducks – teal, wigeon, shelduck, and it was good to see a decent size flock of Lapwing.

recording of teal and wigeon – the wigeon are the whisting sounds and the teal are the regular metallic sounds

Handsome male Stonechat and his mate in front of the hide

Closer to me was a male Stonechat and his mate, while in the hedgerows on the way out a flock of bum-barrels skitted across. Continue reading “Trimley Marshes Nature Reserve”

Canon EF 100-400 L lens fungus attack

note – this is a Mk 1 version of the Canon EF 100-400 L

A working photographer uses their lenses all the time and probably never runs into this. I was into bird photography for a while, about eight years ago, and had the Canon EF100-400 IS L like every other wannabe bird photographer. In between now and then the field has separated the sheep from the goats – real bird photographers use longer primes, because the birds are always at the long end of any zoom. Or they use astro scopes on manual focus 😉

Anyway, I take time out from birds and photography, because life gets in the way, and I stow the lenses in a relatively cold room. A couple of years back I figured I’d take some long lens pics, and get greeted by this

which makes me curse. Mainly on the front element, though a starting spot on the inner element, which is part of the IS mech. The inner part is magnified by the biconvex front element. The spotty crap is on the inside of the front element, the fine filigree round the edge on the front of the front element. Continue reading “Canon EF 100-400 L lens fungus attack”

Raspberry Pi Camera and Motion out of the box – Sparrowcam

The idea is simple enough – a bird feeder camera on the network, using the Pi and associated camera. Using motion detection software I can pick out the birds. Of course I will also get the feeders swinging in the wind 😉

Although this is about running motion I can use videolan instead to stream the video as a netcam and use motion on a second machine. Videolan streaming

cvlc v4l2:///dev/video0 --v4l2-width 640 --v4l2-height 480 v4l2-chroma h264 --sout  '#standard{access=http,mux=ts,dst=0.0.0.0:8082}'

is nice on the Pi, because it seems the camera can do the h264 in some sort of hardware/accelerated mode in the V4l driver. I can then watch the birds with realtime update rates on my LAN. That’s for another day…

Up to about mid 2014 it used to be a load of hurt to run Motion and the Raspberry Pi camera because there were no videoforlinux drivers for the camera. That way you don’t get a /dev/video0 for the Pi Camera and needed workarounds for Motion.

Now there is a driver which you’ll already have on a Raspbian install, and it’s easy to use. right out of the box. Continue reading “Raspberry Pi Camera and Motion out of the box – Sparrowcam”

Lackford Lakes ringing with the sound of Teal calls

Tucked away off the A1101 it’s easy to overshoot the turnoff because the bend of the road means the sign isn’t visible till you are nearly on the turn – even knowing that it caught me out. The low winter light was a treat on the leafless trees, painting them this lovely golden colour.

A lot of the water was still ice-bound, with a few channels of open water. All over the sailing club lake there was a marvellous ringing sound of teal. Not worth recording however since it sounded like the RAF were warming up their afterburners at RAF Honington.

The island only seemed to hold about twenty teal but their calls rang out over the water sounding like many more. I had the reserve largely to myself, with only a couple of photographers with hardy camo gear in the morning.

Visitor centre - newly upgraded in January — Visitor centre – newly upgraded in January

Monday seems to be the quietest day – the visitor centre wasn’t open though Suffolk Wildlife Trust did leave access to the toilets which is a kindness 😉 The small birds were staking out territories in the hazel coppice which was alive with the sound of competing great tits, which seem early to me – they haven’t started seriously marking out territory nearer home.

Lackford Lakes SWT

Norfolk in January

January has been quite sunny and mild this year so I visited the snowdrop walks in Walsingham abbey gardens. It was turning colder for the first day of the snowdrop walks

Only a few other people braved the cold on the first day

but it was a decent show for the end of January!

Continue reading “Norfolk in January”

Oxford Real Farming Conference 2015 – making a remote farm camera

This is a description of how to make a remote farm camera. Smallholders don’t always live on site, or you may have an island site somewhere without power. The simplest solution to get pictures from a remote site without power is to use a 3G trail camera and these work very well for tracking wildlife.

The trouble with this solution on a farm is that animals are meant to be on a farm all the time, Trail cameras look for warm-blooded critters so mammals and birds will set it off all the time, making this an expensive operation in MMS messages, which seems to be the preferred method. Even if you get a MMS bundle, trawling through the false alarms will bore you.

What we wanted of a remote farm camera

was to be able to check on how things were going, and whether something has been damaged by stormy weather. A CCTV camera on the farm would be fine, but the problem with this is the power drain, and getting the pictures back. If we had mains power this would be a lot easier, we could use a 3G CCTV DVR with remote access capability. You can easily get 12V CCTV gear, but the power drain of a typical DVR and camera is quite harsh – typically 1A or more. A typical leisure battery is 80Ah, but you should only use half of the capacity of a lead-acid battery that to avoid reducing the service life of the battery, and you must never fully discharge it. This gives you a battery life of less than two days.

Our remote farm camera uses a Raspberry Pi Model A and associated camera to take a picture every 15 minutes in the daytime and upload it to a website

1501_rpcam02 — Example picture from the camera

Continue reading “Oxford Real Farming Conference 2015 – making a remote farm camera”

The end of the road for Britain’s sound recording clubs

The Internet has done for many older forms of exchanging information – physical newspapers and magazine curculations are a shadow of their former selves. Much of this is Schumpeter’s Gale at work. it simply makes it easier to share information and ideas by disntermediating. The publishers and gatekeepers of the old world are rendered redundant. This isn’t an unalloyed win – they performed a role in screening out the rubbish, and this role has now moved to the search engines to try and make sense of the multimedia firehose pointed at your face.

the logo of the former British Sound Recording Association

People moaned that printed publications tended to favour articles that promoted their advertisers’ products. I’m not quite sure that Google adsense is necessarily a step up from that, but being able to share audio, video, images and writing all in the space of a generation is great.

The Long, Slow Vanish Of Britain’s Illustrious Recording Clubs

I came across this topic in a throwaway line in one of the Wildlife Sound Recording Society‘s newsletters, to wit

When the Society was formed, back in 1968, there were many tape recording societies around the country, today there are very a few. A google search only found one other. WSRS has stood the test of time because of the society’s specialist interest.[wildlife sounds]

Paul Pratley, WSRS secretary 2014

and Google was indeed my friend, it’s possible that Paul was already behind the times. The British Sound Recording Association closed its doors in a meeting in Oxford, to be ratified in November 2014.

NPR has a short radio piece with a few snippets culled from the BSRA’s last meeting in Oxford in June 2014. On the face of it it this seems bizarre – in a world full of podcasters and with sound being used more and more for non-music uses it puzzles me how and where the BSRA failed to move forward. I was never a member because I didn’t see what I could learn from it, and I am not a competition guy – I have never been, either in the fields of sound recording or photography, despite the fact than I manage to take pictures and field recordings that people license. I don’t decry competitions or competing – I simply don’t understand.

This May the BSRA voted by a significant margin of 17 to 9 to wind itself up and cease operations in November.

The problem was called out over forty years ago – if sound is about all about music for you, buy a a good stereo system, not a tape recorder

Dropout called out the problem, in his valedictory column in the last issue of Tape Recorder magazine [ref]Tape Recorder, April 1970 page 173; you can find back issues in PDF at http://www.americanradiohistory.com/ – look for Studio Sound in Audio and Recording[/ref] issue before it became Studio Sound.

RECORDING BEGINS WITH A MICROPHONE
Recording begins, oddly enough, with a microphone ; and what your amateur recordist lacks is access to signals which are worth recording, if his interest be confined to music.
Oh, something can be done along those lines ; but how many tapes have you made which
you can replay with the kind of musical satisfaction you get from your chosen repertory
of discs? I’ll bet it’s very few ; I know it is with me.

But then, I long ago abandoned that fantasy, and began to derive my reproduced music from the radio and the gramophone. I use my recorders—three mains’ machines and a battery-portable—for other things; and when I say use, I mean use.

But, with reluctance, I have come to the conclusion that most amateur recordists have no interests with which tape can help them or—which is more likely—they have not the imagination to see what those interests might be.

Dropout, Tape Recorder magazine, April 1970

I was a child when he wrote that and never read it, but there was something magical about going out with a EL3302 cassette recorder and bringing some of the birds back in with me from the garden. The sparrows have now left my parents’ garden in London, indeed for reasons unknown they have left the city en masse.

Sparrow calls in Ipswich

It would have been nice to have had some of those old C60s with London sparrow sounds from the 1970s. Not particularly because they would have sounded that different, probably, but as a memento of flocks long gone.

The Internet has fostered a new breed of sound hunters – and phonography, sound art and field recordists are well represented. It’s not clear to me how the BSRA lost its mojo, but I admire them for having the honesty to recognise it. I do wonder if the contest mindset is perhaps an anachronism in today’s environment – the whole open-source and mashup culture of, say, freesound is a world apart from the highly structured approach of the British Amateur Recording Contest. I wouldn’t know where to start with the latter.