Raspberry Pi camera after several years outside

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.

damaged Raspberry Pi lens
you can just about see the grungy effect on this damaged Raspberry Pi lens which was outdoors for a season. The mechanical marks around the outside is because you have to break the glue to get the lens out. I did not mechanically damage the lens.

That didn’t respond to pretty aggressive scrubbing with isopropyl alcohol (IPA), and the Pi lenses are proprietary.

the lens on its own
the lens on its own

The back side of the lens not facing the elements looks fine

Sensor side of the lens
Sensor side of the lens

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.

Pi camera behind glass
The Pi camera is still bright-eyed after three years in the outside, behind a glass microscope slide

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”

Laverstoke Park Tea Brewer

Laverstoke Park Farm is a UK site with specialised knowledge of Elaine Ingham’s methods. Sadly their farm shop has closed, we dropped by on route back from holiday last week in the hope of buying a bag of their compost (to inoculate our soil and compost heaps), but no joy, so we’ll email them in the hope of being able to buy a bag or two, or maybe even visit (it looks fantastic!)

We had invested recently in a small compost tea brewer which Laverstoke Park developed, to learn more about how it is done, before we try this on a bigger scale. We have used compost extract rather than compost tea to date as it is easier and safer.

The kit is basically a 3W aquarium pump, an air stone and bucket

Air stone in bucket
Air stone in bucket
Air stone running
Air stone running

The kits came with some microbes in a tube, but the tube seemed to be out of date. Sadly our first attempt with this mix failed as the pump fell from its perch (no harm done, fortunately) and this, admittedly early aborted, brew didn’t appear to contain much exciting under the microscope.

We are now going to wait until we have some promising Oak Tree compost (from heap 160901 , or heap 160910 if either look good under the microscope) or have some Laverstoke Park compost before we try using the brewer again. We’ll keep you posted!

Field recording using an iPod mic input and SpectrumView

recording sound using a smartphone is like a dog’s walking on his hind legs. It is not done well; but you are surprised to find it done at all.

After Samuel Johnson

The smartphone/iDevice is the preferred window to the world of many people – it’s small, it’s handy, it does everything. It’s always with you. And it will do field recording, of sorts.

The internal microphone is usually a noise cancelling microphone designed to favour nearby sounds over ones far away – usually by letting ambient sounds sneak onto the back of the mic capsule to cancel out the ambient sounds impinging on the front. You, being closer to the front and shaded from the back cancel out less. Crude, but it sort of works.

Use an external microphone, not the handset one

That’s not where you want to go as a field recordist, indeed if you could discriminate against your fumbling and breathing noises you’d be better off 🙂

You want to be able to use an external mic. Omni for general run and gun ambient drive-by recordings, and a directional/shotgun mic if you want to pick out a particular birds. To use the latter well you need to be able to hear what you’re doing. Shame, is one of the big failings of smartphone audio is that your can’t record and monitor at the same time. It’s not unreasonable, you rarely want to hear that much of yourself in a phone conversation.

You need an external adaptor lead to convert the 4 pole headphone socket to a stereo headphone + mono microphone connector, these are cheap enough on ebay

You can’t do stereo microphone recording this way, it’s mono only. The input provides plug-in-power to energise electret mic capsules, because this is the typical active device in a phone headset.

Testing frequency response and sensitivity

I tested the frequency response using Rightmark audio analyser, and it looks good enough

Frequency sweep - this is good (the vertical scale is highly expanded)
Frequency sweep – this is good (the vertical scale is highly expanded)

Going in with 1k  tone at -67dBu and 150Ω source impedance the tone level was -32dBFS RMS   and with the tone off the signal was -70dBFS RMS implying a self-noise of -105dBu [ref]44.1kHz sampling, 22kHz BW, PCM, manual gain using the app SpectrumView[/ref] Which is acceptable for urban field recording, though not stellar.

Big FAIL in the field – no monitoring

The big trouble, however, is that you can’t hear anything through the headphones, so you can’t aim a directional mic. Which makes the whole rig a bit crap to use in the field, and this doesn’t seem to be fixable.

There are other bits that grate – for instance the iPod doesn’t always pick up there’s an external microphone, so you can end up viewing the internal mic instead. Then there’s the usual rattiness of apps all round, about 1 in 30 times it just hangs outputting trash on the screen. In general, as a field recorder, smartphones suck. They can be used, but anyone who has used a real field recorder will miss the positive action of real buttons, real record level controls, real metering, and yes, being able to hear what they are doing.

Wild Mountain Echoes has a good summary of the sort of hurt associated with smartphone audio recording. Dr Johnson was right. It can be done, just not well.

Big WIN in the field – live spectrum display

Being able to watch a live sonogram using spectrumview is pretty awesome, and it’s a good sonogram, too, quite well suited to general bird sounds.

The best of all worlds, use a field recorder before the iPod!

It is not done well; but you are surprised to find it done at all.

Best not argue with Dr Johnson 🙂 As a recorder my iPod was flaky and with an input noise level some 20dB off what it could be and mono it’s nothing special even when it does record.

You can get the sonogram by feeding the iPod or smartphone/i-Device downstream of your field recorder – simply use a headphone y-splitter out of the recorder with one side going to your headphones and the other to the iDevice input, and set the gain of the iDevice waaaay down. You don’t have to record with it.

You now have a reliable recorder, decent mic preamps, you get to monitor what you record and if the iDevice throws a wobbly then you still have a good recording. But you how get a lovely spectrogram in live real-time. This is something that’s really excellent. In an ideal world the spectrogram would be built into the field recorder, however running it really hammers battery life so it’s good to have it optional. And it needs to be in colour.