Noisy screen


My screen makes a quite loud high pitched noise when turned on.
So all screens do that or is mine faulty?


Here’s a spectrogram I recorded. You can see me switching the screen on and off. When it’s on, we can clearly see 3 frequencies above 1khz


I have the same symptoms, and would like to know why / how to remove it if possible.

I have the same, and it is a bit annoying.

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Hey guys,

Yes, that is completely normal, that small high pitching sound when the phone turns on is perfectly okay and doesn’t mean that anything is faulty.

Imagine it like being Windows XP boot-up sound (that nice little melody), just this one is being caused by electronics.

Hope it’s not too much trouble to hold off that sound for one second! :sweat_smile:


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Which component is it? I’m not sure it’s the screen, even if when turned off it’s silent

I did some tests and the noise is not present when starting the phone without SD. While leaving the SD slot empty, no noise, even when turning screen on.
As soon as SD is inserted, the noise starts. Then it stops when turning screen off. However it comes back even if removing SD. Only way to get rid of it is to start phone without SD and never inserting it.

@faxm0dem, thanks for the info.
We are not sure what’s the cause of the noise and I hope that you can cope with it. We’ll look into removing this in our future kit revisions.

Thank you for your understanding

That was interesting to know, I was instantly thinking that it was the PWM of the display backlight that was causing it. I will look into this more in the close future…

Please, do let me know too when you find the source of this as I’m also genuinely interested in what’s causing this too :slight_smile:

I have now found what causing the high pitch noise, and it is what I first guessed.

It is caused by the PWN control of the screen brightness.

Why it did disappear when starting without the SD-card is because the display brightness setting is stored on the SD-card and the default (when not found) is full “blast” (i.e. no PWM pulses).

The frequency of the PWM is 5 kHz, which is clearly visible peak in the video that @faxm0dem include previously, and also shows on the oscilloscope that is connected to the BL-pin on the display.

By simply changing line 123 in MAKERphone.h from:

#define LEDC_BASE_FREQ 5000 // use 5000 Hz as a LEDC base frequencyF


#define LEDC_BASE_FREQ 10000 // use 10000 Hz as a LEDC base frequencyF

The sound will than not be as noticeably anymore, at least not to my old ears.

BTW, @robertCM the sound is not just for one second, it is constantly as long as the display brightness is reduced.

@Blixten Yes, the sound is a lot less noticeable when you increase the base frequency!

However, even if you increase it up to 20kHz, you can still hear it if you bring it very close to your ear.

Lowering the screen brightness will always produce some sound since the frequency is much lower and there is just no way around that by adjusting the software.

You can play with it some more for the purpose of research but it’s highly unlikely that the sound will be completely silent at any point. :slight_smile:

We’ll keep working on it, thanks!


Yes, you are right. I also tried to increase it outside of the hearing range (above 20 kHz), but when measuring the PWM-signal with the osciloscope it was actually at about 10 kHz (i.e. within normal hearing range, 20 Hz - 20 kHz). So it seems that 10 kHz is the maximum the current hardware can handle.

But that is okej for me at least, as I said it’s less noticeably then at 5 kHz, so I’m happy with it.

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