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Author Topic: Noises on the headspeaker connector at power ON and at power Off  (Read 622 times)

JFP74

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Noises on the headspeaker connector at power ON and at power Off
« on: November 09, 2017, 01:18:32 AM »
For information, Teres sound level is quite low when we use integrated audiospeakers, even at maximum sound volume, so we connected it on external speakers throw the headphone jack output.
Sound is very good but at power OFF and at power ON, very loud noises occurs during 3 second.
These noises are not present in the integrated speakers.


LubOlimex

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Re: Noises on the headspeaker connector at power ON and at power Off
« Reply #1 on: November 09, 2017, 02:41:27 PM »
This is expected, because the headphone out jack can also used for serial debug. During u-boot it is always set as serial debug and that is why you hear the noise in the beginning of the boot. Once the kernel gets the control over it, switches it to audio output.

There is a script in the official image that can be executed via the command line to switch between the modes. This would allow you to use the audio jack for debugging even after the kernel had started (you lose audio out of course) - it is I believe "debug_switch.sh" or something. I don't think that there is a way to disable this noise in the initial few seconds of a boot, however.
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JohnS

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Re: Noises on the headspeaker connector at power ON and at power Off
« Reply #2 on: November 09, 2017, 02:55:51 PM »
I expect you could rebuild u-boot with the console disabled (or there may be a bootargs value to disable it).

John