[OpenTRV-dev] Audio/FFT thoughts

[Damon Hart-Davis]

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