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Hello everyone, today we are going to learn about the control of backlight in ordinary laptop EC

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This lesson is divided into two parts,

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which are the introduction of Hall components and the control signal of the EC to the backlight

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Firstly, Hall element is a kind of magnetic sensor based on Hall effect,

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also called magnetic induction element

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It has a VIN pin, a GND pin, and an OUT pin

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VIN is the power supply, provided by 3.3V standby voltage,

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GND is the ground, OUT is the output pin,

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the external name is LID#

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When there is no magnetic field, or no magnet near the chip,

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its output pin outputs a high level of 3.3V

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When there is a magnet or a magnetic field near it,

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it will pull the output pin low ground, output low level

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This Hall element in the mainboard is a 3-pins chip,

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its appearance is similar to the ordinary transistor and MOS tube

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Next, let's take a look at the EC's control of backlighting

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Here we introduce three kinds of signals

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One is the LID signal,

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which is also called the lid switch or the sleep switch

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In the shutdown state, this signal is used to determine whether it can be turned on

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When the signal is low, that is, when a magnet holds on to it,

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the machine will not turn on

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There's a magnet on the border of the screen, and when we close the cover,

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the magnet grabs the Hall element, pulling down the LID# signal

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When the EC gets this low LID# signal,

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the EC knows that the machine is in sleep state

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At this time, EC does not allow startup

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After boot, if the LID# signal is pulled down again, the EC will turn off the backlight

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After receiving the LID# low signal, the EC will issue a backlight to close the control signal

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Common names for control signals include LCD_BACKOFF, LCD_BLON, etc

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When we open the cover, the LID# signal returns to the high state,

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and the EC will issue a backlight on signal to turn on the backlight

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There is a signal called brightness adjustment,

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that is, when we press the keyboard shortcut key,

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the EC receives the shortcut key command, through the brightness adjustment signal

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to adjust the brightness of the screen backlight

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Okay, this is the EC's control of the backlight