Add new output mode MOZZI_OUTPUT_PWM_PP [enhancement]

[evil-gears]

Hello, I would like to suggest a new PWM output mode for people like me who have no external DAC but still want a louder audio output and have a spare GPIO pin.

The idea is: in this new mode, MOZZI_AUDIO_PIN_2 would output exactly the inverse of MOZZI_AUDIO_PIN_1, much like in this example:

Since Mozzi already supports stereo output on those pins, I think that shouldn't be too hard. The only catch is that when idle (no sound playing), MOZZI_AUDIO_PIN_2 must always be held at LOW so that it does not burn out the driver/speaker the pins are attached to.

[evil-gears]

Just for context, I am driving my speaker using an H-bridge, which is more robust, produces a louder volume and also more suited to the PWM signals of the Arduino board. The drawback is that it needs an inverse signal for it to reach full volume, hence why I'm suggesting this mode.

[tomcombriat]

Hi,

I think I would do this in the user sketch , using the StereoMode, for instance:

int asig= aCos.next();
return StereoOutput::fromNBit(8, asig, -asig);

This is especially true as having inside the library does not makes the user's life very easier (it does for the HIFI mode because the number of bits the platform can output is not necessarily the same for all platforms).

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The only catch is that when idle (no sound playing), MOZZI_AUDIO_PIN_2 must always be held at LOW so that it does not burn out the driver/speaker the pins are attached to.

I think this is more done in electronic by adding some coupling capacitors to the outputs so that it is gnd centered. Note that, even in mono, an output of 0 from updateAudio() will produce Vdd/2 in average in PWM mode: the signal is not holding to 0 when silenced.