passband frequency detection

Hello,

I have a signal sampled at 16kHz, and I would like to detect when any
of the frequency components within 0.5Hz-10Hz is above predefined
limit (say -10db).

Because of high sample rate I expect that the resampling/decimating
input signal will be necessary.

Doing FFT just for yes/no answer seems like an overkill.

I was considering bandpass filter with magnitude comparator.

Are there any other solutions?

Could I get away (any cheaper in terms of MIPS, RAM) with couple of
goertzels?

Just thought of asking before starting to code.

Regards, Mitja

On 12 Jun, 14:15, Korenje <kore...@yahoo.co.uk> wrote:
> Hello,
>
> I have a signal sampled at 16kHz, and I would like to detect when any
> of the frequency components within 0.5Hz-10Hz is above predefined
> limit (say -10db).
>
> Because of high sample rate I expect that the resampling/decimating
> input signal will be necessary.
>
> Doing FFT just for yes/no answer seems like an overkill.
>
> I was considering bandpass filter with magnitude comparator.

That seems like the obvious choise.

> Are there any other solutions?

Probably.

> Could I get away (any cheaper in terms of MIPS, RAM) with couple of
> goertzels?
>
> Just thought of asking before starting to code.

Use the simple solutions first.

Rune

Korenje wrote:

> Hello,
> 
> I have a signal sampled at 16kHz, and I would like to detect when any
> of the frequency components within 0.5Hz-10Hz is above predefined
> limit (say -10db).
> 
> Because of high sample rate I expect that the resampling/decimating
> input signal will be necessary.
> 
> Doing FFT just for yes/no answer seems like an overkill.
> 
> I was considering bandpass filter with magnitude comparator.
> Are there any other solutions?

Do it vice versa. Make a bandstop filter with a variable stopband and 
measure the RMS power outside of the stopband. This will probably cost 
you about one MIPS and 16 bytes of RAM.

Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

http://www.abvolt.com