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VS1103b Feedback Eliminator Demonstration Board

Posted: Tue 2020-02-25 16:33
by cjh

I have a VS1103b Feedback Eliminator Demonstration Board. I've programmed it with VLSI firmware 'fbe_v110'. I'm using its on-board microphone. I've wired the headphone to an external active speaker via a 470R/3n3 filter and a 10u/10K DC decoupler (as described in you documentation).

The unit seems to be working, I speak into the microphone and can hear my voice coming out of the speaker. However, I'm yet to be convinced that the unit is helping with acoustic feedback. I fully understand that this unit can't eliminate feedback in all circumstances.

The manual says that holding down SW2 will bypass the FBE algorithm. My tests indicate that feedback is actually worse when the FBE algorithm is active (SW2 not held down). So I'm puzzled.

So some questions:

Why does feeback appear to be worse when FBE algorithm is active (SW2 not down)?

Do switches SW1 and SW3 do anything?

I assume that the left/right output channels are outputting an identical signal (given that the input is monophonic) is that correct?

Am I using the latest version of the firmware (fbe_v110)?

Do I have the latest version of the VS1103b Feedback Eliminator manual (Rev. 1.10)?

Is the source code for the firmware available for download? If so, where do I download it from?

Thanks, Chris.

Re: VS1103b Feedback Eliminator Demonstration Board

Posted: Tue 2020-02-25 16:55
by pasi
The code is from 2009, last compiled in 2011, so recollections are a bit hazy.
Some quick answers:
- fbe 110 is the latest.
- If I found the right code, it looks like the left output provides in-phase signal, and the right output outputs inverted signal. (So-called differential mode)
- Only stationary signals (feedback loops) are suppressed. If the mic input overflows, then the eliminator cannot really work.
- SW1 and SW2 do not do anything, SW3 should be connected to GPIO3. If you see the DREQ-LED switch state when pressing SW3, the board has that connection.

The code isn't in a VSIDE solution format at the moment.

Re: VS1103b Feedback Eliminator Demonstration Board

Posted: Wed 2020-02-26 10:16
by cjh
Hi Pasi,

Thanks for your response.

I'd be happy to have the source code in any format. I've previously implemented commercial VS1000 projects using your old command line compiler.

Regards, Chris.