Overclock the Miix 510 screen backlight PWM | 给Miix 510的屏幕PWM超频

When I was still in elementary school, i found if i shake my hand in front of a old school CRT display, there are many shades of my hand around my actual hand. Beside of that, it also strain my eyes quickly.
我上小学的时候发现如果你在旧式大脑袋显示器前晃动你的手,你会看见多个你手形状的类似影子的东西。

Nowadays this effect also appear on some modern LED displays, because the usage of low frequency PWM backlight.
现在的一些LED灯也会有这种问题,因为这些灯用了低频率的PWM来调节光的强弱。

Once this effect is observed on certain LED light, be aware of that light can strain your eye.
一旦你发现有的LED灯有这种现象,长时间在这个灯下就会引起视觉疲劳。

Sometimes you can get rid of this effect by overclocking the PWM.
这种低频闪的光源会使人很快的产生视觉疲劳,但有的时候给PWM超个频可以解决问题。


 

On modern flat-panel display, PWM is a common way to adjust the brightness of LED, check out video below can help you understand what is PWM and how PWM worked.
现在的屏幕有很多都用PWM来调节亮度,先看看这个视频来了解一下PWM是什么以及PWM的工作原理。

In the beginning  I gonna explain how your eye get strained by screens:
先解释一下你的眼睛是怎么疲劳的:

Old-school CRT display have very high refresh rate due to the nature of CRT usually 120 Hz, means it can display up to 120 frames per second(fps), but computer usually generate 60 fps of graphic, so what other 60 frames?
老旧CRT显示器通常有高达120 Hz的刷新率,也就意味着它一秒钟能显示120帧的图像,但是通常电脑输出的刷新率只有60帧一秒,那剩下的60帧呢?

The monitor need to either by guess, interpolate previous frame or fill with black frame. Due to the cost and design hardness, most of CRT monitor used the last way.
这个显示器要么去猜,要么重复上一帧,要么用黑帧充数。出于成本和设计与加工难度考虑,大部分的显示器都是用黑帧充数的。

Can you imagine there are something super bright and keep flickering 60 time per second? That’s the way how not to use a computer.
想想一下一个很亮的东西在你眼前一秒钟闪60次是什么感受。

So what’s the relationship with CRT display and LED with PWM? Good question.
那CRT显示器和PWM调光有什么关系呢?

There are 2 ways to change the brightness of LED, by either change the current or PWM. The circuit for change the current are complicated and expensive, so most of the LED use PWM to change the brightness.
改变LED的亮度有两种方式,一种是改变输入的电流,另一种就是用PWM。同样出于成本和设计与加工难度考虑,大部分的LED用的都是PWM来调节亮度。

Unlike tungsten bulb, flicker have no negative impact on LED itself due to the nature of LED, as previous video said, higher the duty cycle result in longer time of of LED been turned on, so seems brighter the LED is.
LED的工作原理与特性决定了这个东西和钨丝灯泡不同,LED不怕闪。前面的视频里讲了,占空比越低,LED在一个周期内点亮的时间就越长,LED也就看起来越亮。

When duty cycle reach 100%, the shade effect disappeared, simply because there are no off time for LED, but that’s way too bright on this screen for me to study on.
当占空比低到了0,手旁边的阴影就看不见了,因为这个时候LED是常亮的。但是这个屏幕太亮了,根本没法用来学习。

By the way, shake your hand toward the light source is a easy and effective way to check a LED light source will strain your eye quickly or not. If no shade seen,  less strain to your eyes.
顺便说一句,冲着光源晃动你的手来看有没有阴影是看一个LED灯伤不伤眼睛的最简单有效的方式。如果你看到了手的旁边有阴影就说明这个LED灯长时间用会比较伤眼,如果没有或者基本看不到就说明这个LED灯还是不错的。

I did a little search on the internet and i found the screen driven by Intel Graphics have a programmable PWM which can use the integrated function inside of Intel SDK to tune the PWM frequency.
我上网稍微查了一下,由Intel核芯显卡驱动的电脑屏幕的PWM基本都是可调的,用Intel SDK里的函数写个小程序就可以解决问题。

Sketch.png
Click the picture to download it at Github.

This is a open source program written by tpurtell in C# to change the PWM frequency with Intel Graphics.
这是一个Github上tpurtell用C#写的一个开源的用来调节PWM的小程序。

WARNING IN ADVANCE, OVERCLOCK CAN DRAIN THE LIFESPAN OF PWM, TRY IT AT YOUR OWN RISK!
超频前先提醒一下,超频PWM是折寿的,小超怡情,大超伤身,强超灰飞烟灭!谨慎行事,三思而后行!

The program tells me it only have 200 Hz of PWM frequency. Bad!
这个程序最开始显示这个屏幕PWM的频率只有200 Hz。。。。。。

After overclock the PWM to 1100 Hz, the shade disappeared.
之后我把它超到了1100 Hz,阴影没了。

IMG_20170925_1433455.jpg
After PWM was overclocked to 1100Hz, no shades seen around the pen

I tried to overclock it to higher frequency, but i noticed there are noticeable whistle sound when frequency go more than 1200 Hz and that is not good. So I leave it at 1100 Hz.
我试了一下,这个频率好像能超到挺高,但是我发现只要频率超过1200就能听见屏幕有啸叫声,听起来像PWM在喊mmp(笑)。于是我选择超到1100 Hz。

So 60HZ of flicker light is harmful to our eyes, 200 Hz harmful, too. We just made it 1000+ per second, will it affect our eyes? The answer is definitely yes, but 1000 Hz is way much better than 60, and the higher the frequency is, your eyes will more forgive the flicker, when you have a high frequency PWM LED.
60 Hz的屏幕伤眼,200的也伤眼,那1000多就不伤了?确实伤眼,但是1000比60高到不知道哪里去了,频率越高,你的眼睛就越察觉不到,低频闪烁导致的视觉疲劳也就会越小。

In fact, on higher end monitor, the frequency of PWM can reach 8000 Hz even over 10000 Hz
事实上,现在的一些高端显示器的PWM调光频率都有8000多甚至10000 Hz。

Overclock do harmful to the hardware, but I don’t need a computer run over 10 years since it will become obsolete. So if your computer have low PWM frequency and it strain your eye, overclock it may be a good solution.
虽然超频折寿,但是我也不指望这个电脑能用10年,因为这个东西不用5年就会彻底过时。与其让低频PWM伤害你的眼睛,不如用5年的寿命换我大学4年的用眼健康。

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