sounds, sensors, stones
A lovely little stream near the path to Scorhill stone circle, it was worth a longer recording. Starlings are starting to mass in the Autumn, and they provide some counterpoint to the running water in this binaural recording. Nice not to have to filter anything – straight out of the recorder apart from trimming the timeline and bringing the gain up a little bit.
The original OpenEEG filter design had a poor performance that made me reluctant to construct that project, although the price was right. I had proposed a replacement elliptical filter
using this design
which turns into this
I had the devil’s own job trying to measure this, trying to avoid plotting it out by hand the old way, although that would be the right way 😉
Running a Wien bridge oscillator through it showed me I had one null, which was rough, because I’d ordered two 😉 one was at 148Hz, and another very very faint one at 534Hz, which was wrong, it should be at 272Hz. Scoping the output of the first section showed that was the culprit, I had put in 1.8k as R23 instead of 6.8k. My nulls are now clear and in the right place. I try sweeping the filter using Rightmark audio analyser. First it moans it can’t find the 1kHz sync tone, well, yeah, I don’t really expect to find that at the output of this filter. Running stereo with left straight through finds the sync, but Rightmark sells this to young pups setting up their car stereos presumably, so they want you to pay for having any useful low-frequency resolution, and I’m not prepared to pay.
I tried running white noise through the filter and FFTing the result. Connecting it to a USB Behringer UCA202 gives me hum from a ground loop through the scope and computer, so I recorded the output using a handheld battery audio recorder to get rid of that. The sound is really quite strange
Unfortunately the FFT has no real resolution of the dips, the second is lost in the mush although it can be seen when manually sweeping the filter. Still, how did I do given the real filter is better than the FFT sweep? Say the passband is about -28dBFS, at 128Hz I am about -66dBFS, about 38dB down. OpenEEG were at about -16dB there, so I have roughly doubled their performance. Trash at fs/2 + x tends to alias to fs/2 -x, ie the HF end of the passband, 64Hz. The highest of the Mind mirror filters was at 38Hz, so I am interested in the attenuation at say 128Hz + (128-40) = 216Hz, since rubbish up here will fold down to the MM high frequency filter. That’s about -80dB, so I am about 52dB down by then, again about twice OpenEEG’s -24dB. It’s not quite the -60dB which would dump a full-scale signal at 216Hz into the 10-bit quantisation noise, but it’s close.
What this filter won’t do is help you against mains hum for 50Hz. It starts to roll off starting about 70Hz, so that hum will go right through regardless. It is also not a candidate for massive miniaturisation, those caps are big. Sure, it can be built tighter on a PCB, but it won’t ever be tiny. No point in buying the Olimex box for the OpenEEG product if I go that way, and no point running the SMD version.
I figure this is a creditable improvement on the openEEG filter, almost worth manually plotting out the frequency response to see what it is uncluttered by FFT artifacts
I constructed this with a NE5532 run off +/-12V, because I wanted to see it running right. The next stage is to try a LM358, I am not sure such a nasty device will have the performance for an elliptical filter, which needs a high Q for the nulls. But it is a very low-frequency filter, so I may still have enough gain/bandwidth product. I can pull the 5532 and see if the nulls shift or soften. It’s tough that OpenEEG has only a +5V rail. That’s within spec for the LM358, but the output will only swing from 0V to 3.5V, arguably I should bias these mid-rail to 1.8V rather than 2.5V . Ideally I want a quad rail to rail 5V opamp, something like TI’s LMC660C.
This weekend Glastonbury hosted the Osiligi Maasai Warriors, a performing group from the Kenyan Maasai community of Olepolos.
It was a pleasure to listen to them at the Fair Field on a lovely sunny day, where the public had been invited for a picnic at 3:30 – here is their remarkable performance
Continue reading “Osiligi Maasai Warriors at Glastonbury Fair Field”
This post is as a public service. WARNING – an Olympus E-PM1 camera has some LEFT-HAND thread screws. I’ll show you where these blighters are later.
Manufacturers really seem to hate people taking their gear apart, but I’ve never come across Olympus’s sort of craftiness before. There’s no good reason for them to make these screws left-hand thread, other than to make you strip the soft plastic they’re set into if you have the temerity to try to take your own property apart. Evil bastards. It’s not like a bicycle crank on the left-hand side, where there’s a damn good reason for the left-hand thread.
I quite liked this camera, despite the plastic battery door hinges breaking off after a year. It’s pocketable, but can take a decent EVF if necessary, I have a VF-4. I recently dropped the camera, and on power-up I hear this noise (recorded form about 2cm away). The clunk is fine and has always been like that, the death rattle is new.
Which does not fill me with confidence that this camera is long for this world, although the pictures are fine. I can almost count the plastic gear teeth wearing, and it’s loud enough to draw attention, which is a drag for photographing people. I suspect it’s slower off the mark than it used to be, too. So I thought I’d pop the back and take a look to see if something is obviously wrong. Continue reading “Olympus E-PM1 camera left-hand thread screws to catch fixers out”
Just when I thought the remote Olympus recorder is the way to go here, along comes a promising new Pi solution for remote recording – this looks to be low cost and small. What more could a fellow want?
Decent instructions and specs, for a start 😉 Australia seems to have a vibrant electronics tinkering community, and Matt Flax of audio-injector has come up with a dinky little recording sound card suitable for the Pi Zero, without the sort of stupendous kernel-compiling hurt associated with the now discontinued, Wolfson/Cirrus sound card. Matt even used Cirrus tech under the hood, kudos to him for making it work in the Pi environment- I guess the Pi has advanced in standardising add-on gizmos too.
You can buy the AudioInjector Zero from Australia, only to discover postage is about as much as the sound card, so Google helped me discover that you can get it in the UK from Amazon, who drop-ship it at a much more acceptable price of £12.50 delivered free if the total order is > £20. So I go get one.
Nice. No GPIO connectors, though you get a nice bunch of extra audio connectors to make this connect to phono jacks. How does that work, then? Continue reading “Raspberry Pi Zero audio recording with the AudioInjector hat”
There is more green space and trees around me where I am now, with many more garden birds, though no sparrows1, and occasionally some tawny owls in the night.
Tawny owls, recorded ME66 handheld
So thoughts turn to a garden recording gizmo again. I have enough power, and a network connection to a shed, a oddly wind-sheltered location and many trees nearby. For short term recordings in the field I am still in favour of the timed field recorder approach, but for the garden where I have power and data the Pi still scores. You don’t have to fiddle with it, it’s entirely remote controlled. Many years ago I had a PC in the garage which was the music server, I used a piece of software called loop recorder on that. This cat fight is one of my favourite urban recordings from that time.
although I was really trying to record a hedge full of sparrows. A loop recorder lets you go back and catch things like that, and the microphone would be much closer to the area where the owls are.
So I thought I’d revisit this Cirrus Logic audio card, particularly as a case for a Pi with this mounted was being sold off cheap for £5
The Cirrus is the only audio card for the Raspberry Pi that lets you record sound with it, as opposed to the legion of DAC cards for the Pi. You can, of course, use a USB sound card instead, though that precludes using a Model A if you want to use wifi and have the lowest power.
The good news is that a hero hacker, Matthias Reichl, has sorted out the drivers, it’s now a RPI-update rather than patching kernels and esoteric crap.
The bad news is that the manufacturer discontinued the card 🙁 Having said that, it still seems to be available for about £60 if you work hard enough, GIYF. That’s dear – a Behringer UCA202 is a good Pi compatible USB sound card for about £24, line level input. The Cirrus Logic card offers a bit more sensitivity and on board mic bias. Continue reading “Cirrus Logic audio card for the Raspberry Pi revisited”
This project is about resilience more than energy saving, though it can also be used to save energy. Total costs should be in the order of £100, but there are ways to reduce that by getting some items from Ebay. The idea for the project came from the Transition Ipswich Energy group in 2011. It had to be targeted at a competent DIYer, and is for small scale lighting. This was originally published on TI’s website, which is no more.
This project lets you run lighting off of solar power, effectively storing sunlight for later use. It can be used at home to keep lighting during power cuts, but the same principle can be used to provide power to sheds on allotments, outbuildings or island sites without mains power. Although I have used lighting as an application, such a system can run an electric fence for much of the year if suitable solar panels and battery are used.
The system as described lets you run one or two 12V 1.8W LED lights through the year – my system was able to run mine through the winter and the shortest day where the light would be on from about 6pm to 11pm. In the summer you can also run a laptop computer power supply independently of the main for a couple of hours (these run typically 40W). That is because in the summer you get far more solar energy and you’ll probably use the lighting less.
If you want to primarily save energy or reduce your carbon footprint using solar power, this is not the solution. For that it is best to get a grid-connected solar power installation which will allow you to save energy and get renewable feed-in tariff payments. That sort of thing is on a different scale from this project, and capital costs are usually in the order of several thousand pounds, but the energy savings are much, much greater. A grid-connected solar PV system does not give you resilience against power cuts, because the anti-islanding systems in the grid tie inverter shut the system down if the main power fails, so that a PV system does not send power back into the grid when it may harm power workers trying to repair faults.
I’ve had my Soundman OKMII binaural microphones for over ten years, and they are my favourite mics for urban field recordings. DACS is the UK supplier.
They don’t really work in wind, and they aren’t the quietest, but they are as stealthy as you can get, looking just like earbuds. A decade ago you still looked a little bit of a geek using them and monitoring on a recorder, but nowadays most people are looking at their smartphones, rather than the lamp-post/road they are about to encounter. On the off-chance that they do look up, they will assume you are just another human trying to escape the real world for the virtual one inside your phone, which happens to be a field recorder.
I was going for a general recce on the Somerset levels, looking for interesting sounds. I heard a lot of birds congregating in some trees, and started the OKMII. There was a lovely little flurry of about 100 starlings flying overhead at about 2 and 4 secs against a background of other starlings gathering in the trees
The OKMII isn’t really a birding mic, but it picked up some of the essence of these guys
and then I encountered this ghastly full-scale 0dBFS noise on the left
a bad contact on the left channel. After 10 years these mics don’t owe me anything, but I figured it’s worth a look if a fix is possible. Skinning the foam earpads shows this
It’s possible to separate these with a craft knife along the obvious seam, concentrating on the melted bits. The microphone is glued to the shell with a hole, try and keep this together to expose the contacts on the rear of the capsule. Continue reading “Soundman OKMII repair”
It doesn’t pay to put a Raspberry Pi camera out directly facing the great British outdoors for more than a season even if you can keep the water out of it. I had a RPi Model B and camera doing just that and groused about the lens crazing problem where there seems to be some sort of microbial attack on the lens after a season outdoors.
That didn’t respond to pretty aggressive scrubbing with isopropyl alcohol (IPA), and the Pi lenses are proprietary.
The back side of the lens not facing the elements looks fine
They are not standard M12 CCTV lenses1, so I got to buy another camera board, and used Sugru and a cut down glass microscope slide to try and keep it intact. I can buy aftermarket RPi compatible cameras using M12 CCTV lenses now, but then it wouldn’t fit in the PICE case.
I left this camera out in the open on the farm for a while, and then watching my sparrows on the feeder. It looks like the glass slide technique has been a win, it’s been around three full years and the camera lens is still OK. The slide can be cleaned with IPA and comes good as new. Angling it down slightly reduces reflections and flare, but yes, it is uncoated so flare will happen. I built the Sugru up a but round the top to make a lens hood to minimse the amount of open sky that falls on the glass. Maybe the original Pi camera lens is plastic and gets eaten, although I know to my cost that optical coatings on glass can get hit by fungus too in damp conditions 🙁 Continue reading “Raspberry Pi camera after several years outside”
Wire mesh can make a cheap and portable composting container. We never had much success with this at The Oak Tree farm, probably because the site was very exposed to the wind, but Nigel Griffith at Landews Meadow Farm and Dave Beecher use this technique successfully.
We are trying this again at a new site which is much more enclosed from the wind, and we have the benefit of mains power for pumping. However, we don’t have borehole water, so we had to fill a 220l water butt with mains water1, and leave it to stand for a couple of days to vent the chlorine.
Materials were freshly chipped tree prunings scrounged from some guys who were trimming trees for the council and a combination of hedge trimmings, windfall apples and other green material. These were shredded using a domestic rotary garden shredder to this sort of consistency
Continue reading “Hot composting using a wire mesh container”
