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Re: Motion sensor automated recording with a Sound devices 744t.

Subject: Re: Motion sensor automated recording with a Sound devices 744t.
From: "atl" r0t0pan
Date: Tue Dec 23, 2014 6:26 pm ((PST))
Hi, all.

This is more general info, but I have done prototyping work for notion
sensing on some of the SOC platforms out there (raspberry pi, beaglebone,
etc) to control other devices.  PIR (passive infrared) and FLIR
technologies are readily available for these platforms as are any other
sensory modalities. You could use a combo of FLIR plus a CO2 detector to
trigger an action in whatever hardware you might have handy.  It pretty
easy to accomplish that part.

The hard part is translating the voltage to language the receiving hardware
understands.  As stated previously, knowing the protocol used by SD for
their accessory port is key.  One could derive that by externally powering
the remote and intercepting the voltage over the line related to each
function but that's pretty tedious.  Still, it's likely doable...just as it
has been done for photography equipment for projects like the EIS.

On Dec 23, 2014 5:56 PM, " [naturerecordists]" <
> wrote:

> > Hi there I have a trick question and I thought I should ask it here. I
> have an opportunity to record some captive nocturnal animals in a breedin=
> enclosure and require a way to start recording at night when motion is
> detected. The place I am collaborating with on have a motion sensor setup
> for their camera which is what they use to observe them.
> Daniel,
> Over the years I've tried to use various triggers, sound and vision. The
> first problem is you really need a pre-record function, but this is rarel=
> long enough to get several seconds before the wanted sound to give any
> sort
> of intro.
> There are basically two types of motion sensor. One detects changes in a
> video image and the other triggers on sound. I found video triggering
> impractical as it has to be sensitive to work reliably, and every wind
> movement and passing moth triggers a run. Without a suitably long
> pre-record, sound triggering usually loses the interesting bit at the
> start.
> The question then is how long do you set as a minimum run time, and will
> it
> retrigger without a break? I soon gave up on that one.
> I've been using a Bushnell trail camera (with sound) to record hedgehogs
> and
> it uses an infrared heat proximity sensor (burgler alarm type) which
> either
> triggers too freely or misses slow movements. Also it only runs for one
> minute of video which is fine for counting hedgehogs but not for recordin=
> behaviour.
> The problem with sound triggering is how sensitive you set it, and again
> the
> run time. You need seamless retriggering or long recording periods to get
> useful clean tracks.
> My solution is to leave the recording running continuously, especially
> with
> sound. You get a lot of unwanted stuff, but I go through the recording
> visually with a sound editor, and scrap stuff ruthlessly. I've got
> recordings that way of wildlife I didn't know was around on the
> serendipity
> principle.
> I record MP3 at 320 Ks/s which is good enough for my original sound
> sources.
> I did some critical tests, and found that MP3 artefacts became audible
> with
> my background sounds at 192 Kb/s and below.
> Birdsong compresses well as it is musical, but MP3 replaces random noise
> with bursts of tone. At low rates, white noise makes a tinkling sound, bu=
> at 320Kb/s that is masked enough not to be audible in practice or so I
> reckon. Double check by subtracting an original recording on WAV from an
> MP3
> version. You will probably find that MP3 time-shifts some transients, but
> in
> practice it gets away with that audibly. The "tinkling" artefacts are the
> problem.
> David Brinicombe

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