[OpenTRV-dev] Audio/FFT thoughts

[Kevin Wood]

Yes, I guess you could combine it with a detector to "wake" the more
sophisticated listening function.

Kevin

> I can do all sorts of duty cycles, etc; I really need to get an idea of
> what would actually work.
>
> My instinct is that when the device is getting close to timing out it "is
> occupied" measure it could increase the duty cycle to be especially
> attentive for noises.
>
> Another possibility is to add a crappy but very sensitive high impedance
> low/zero-power mike (eg piezo) on a separate / interrupt input that would
> wake the main system up to listen if anything interesting was happening.
> Dunno.
>
> Rgds
>
> Damon
>
>
>
> On 11 Jun 2013, at 11:47, Kevin Wood wrote:
>
>> Sorry for not being around much lately...
>>
>> I would wonder if 8ms per second is going to be enough duty cycle, TBH.
>> Speech itself is going to be fairly sporadic with long silences in an
>> occupied room and gaps between syllables when the speech is constant.
>>
>> I appreciate that moving everything into software is going to keep the
>> hardware cheap and simple, but I wonder if a minimal preamp, filter and
>> level detector with reasonable current consumption could not be built in
>> hardware. It could be fired up for tens of seconds at a time and might
>> be
>> a more reliable indicator of room occupancy than sampling in very short
>> bursts?
>>
>> Trying it is the only way to find out, though, I suspect...
>>
>>
>> Kevin
>>
>>
>>> Hi,
>>>
>>> Some initial thoughts on audio occupancy detection with the ATmega,
>>> listening out for voice (of a human or their radio/TV being on).  I
>>> have
>>> done no feasibility testing yet.
>>>
>>> My current plan is to (~8-bit) sample with the ADC at 16kHz, in bursts
>>> of
>>> about 8ms (between RTC ticks), using a simple exponential filter to
>>> reduce
>>> to 8kHz samples.  Take 64 samples which should allow me to examine
>>> frequencies in the 4kHz to 500Hz band which probably covers most of
>>> "voice".
>>>
>>> 1) I think that I can probably achieve this sampling rate even at 1MHz
>>> CPU
>>> clock (default Arduino ADC sample rate at 16MHz CPU clock seems to be
>>> 9600Hz and I have a prescaler to play with).
>>>
>>> 2) I only intend to listen when I'm otherwise in danger of thinking the
>>> room unoccupied, and in any case on a low duty cycle to save juice (eg
>>> one
>>> 8ms sample block per minute or less for example).
>>>
>>> 3) I have headroom to boost the CPU speed dynamically to 4MHz if I need
>>> to
>>> (I already dynamically lower it when I need to).
>>>
>>> What is hideously silly about this plan already?
>>>
>>> Rgds
>>>
>>> Damon
>>>
>>>
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>>
>>
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