audio frequency tone detection in software

[Acetronics2]

Hi, Mike

IF a NE567 isn't sufficent to filter the signal ... I do not see what a simple PIC could do better ...

May be a DSPic ... if any amplifier was available in it ...

That said it's a problem of cleaning the signal before filtering it ... and I , personnaly, would add a little signal filtering card before the 567 Input ...

Alain

[mlmccauley]

Thanks for the reply, Alain.

A simple single op amp bandpass filter is used in both the 100 and 1KHz segments prior to the NE567s. I haven't swept them using a variable oscillator and a scope, but I'm sure they're fairly broad. Better than nothing, though, as you say.

I have heard that the Goertzel algorithm

http://en.wikipedia.org/wiki/Goertzel_algorithm

can be used to do this job on a moderately fast (10+MHz clock) uP, but I have no experience with coding such a thing. And as you can see at that URL, the math is not trivial.

A DSP PIC would probably do a great job in this application, but I have no tools to program those chips, and wouldn't even know where to start with trying to do so in assembler. Whatever I do will have to be done in PBP or C.

At any rate, thanks for your reply,

Mike

[Acetronics2]

Hi, Mike

This filter requires floating point calculations ... trig functions are not exactly PbP's best feature nor ...

so, I do not think it could be a good Idea ...

Alain