231 lines
7 KiB
Markdown
231 lines
7 KiB
Markdown
---
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title: Backlight
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sidebar_label: Backlight
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---
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import Tabs from '@theme/Tabs';
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import TabItem from '@theme/TabItem';
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Backlight is a feature used to control an array of LEDs, usually placed through or under switches.
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:::info
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Unlike [RGB Underglow](underglow.md), backlight can only control single color LEDs. Additionally, because backlight LEDs all receive the same power, it's not possible to dim individual LEDs.
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:::
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## Enabling Backlight
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To enable backlight on your board or shield, add the following line to your `.conf` file of your user config directory as such:
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```
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CONFIG_ZMK_BACKLIGHT=y
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```
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If your board or shield does not have backlight configured, refer to [Adding Backlight to a board or a shield](#adding-backlight-to-a-board-or-a-shield).
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## Configuring Backlight
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There are various Kconfig options used to configure the backlight feature. These can all be set in the `.conf` file.
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| Option | Description | Default |
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| ------------------------------------ | ----------------------------------------------------- | ------- |
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| `CONFIG_ZMK_BACKLIGHT_BRT_STEP` | Brightness step in percent | 20 |
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| `CONFIG_ZMK_BACKLIGHT_BRT_START` | Default brightness in percent | 40 |
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| `CONFIG_ZMK_BACKLIGHT_ON_START` | Default backlight state | y |
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| `CONFIG_ZMK_BACKLIGHT_AUTO_OFF_IDLE` | Turn off backlight when keyboard goes into idle state | n |
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| `CONFIG_ZMK_BACKLIGHT_AUTO_OFF_USB` | Turn off backlight when USB is disconnected | n |
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## Adding Backlight to a board or a shield
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<Tabs
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defaultValue="shield"
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values={[
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{label: 'Adding to a board', value: 'board'},
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{label: 'Adding to a shield', value: 'shield'},
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]}>
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<TabItem value="board">
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First, you must enable PWM by adding the following lines to your `Kconfig.defconfig` file:
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```
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if ZMK_BACKLIGHT
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config PWM
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default y
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config LED_PWM
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default y
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endif # ZMK_BACKLIGHT
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```
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Then you have to add the following lines to your `.dts` file:
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```
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&pwm0 {
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status = "okay";
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ch0-pin = <45>;
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/* ch0-inverted; */
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};
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```
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The value `ch0-pin` represents the pin that controls the LEDs. With nRF52 boards, you can calculate the value to use in the following way: you need the hardware port and run it through a function.
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**32 \* X + Y** = `<Pin number>` where X is first part of the hardware port "PX.01" and Y is the second part of the hardware port "P1.Y".
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For example, _P1.13_ would give you _32 \* 1 + 13_ = `<45>` and _P0.15_ would give you _32 \* 0 + 15_ = `<15>`.
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If your board uses a P-channel MOSFET to control backlight instead of a N-channel MOSFET, you may want to enable `ch0-inverted`.
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Then you have to add the following lines inside the root devicetree node on the same file as before:
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```
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/ {
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backlight: pwmleds {
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compatible = "pwm-leds";
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label = "Backlight LEDs";
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pwm_led_0 {
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pwms = <&pwm0 45>;
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label = "Backlight LED 0";
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};
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};
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};
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```
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The value inside `pwm_led_0` must be the same as you used before.
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:::info
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Note that every LED inside of the backlight node will be treated as a backlight LED, so if you have other PWM LEDs you need to declare them in a separate node. Refer to [Multiple backlight LEDs](#multiple-backlight-leds) if you have multiple backlight LEDs.
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:::
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Finally you need to add backlight to the `chosen` element of the root devicetree node:
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```
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/ {
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chosen {
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zmk,backlight = &backlight;
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};
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};
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```
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</TabItem>
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<TabItem value="shield">
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You must first add a `boards/` directory within your shield folder. For each board that supports the shield you must create a `<board>.defconfig` file and a `<board>.overlay` file inside the `boards/` folder.
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Inside your `<board>.defconfig` file, add the following lines:
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```
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if ZMK_BACKLIGHT
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config PWM
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default y
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config LED_PWM
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default y
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endif # ZMK_BACKLIGHT
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```
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Then add the following lines to your `.overlay` file:
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```
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&pwm0 {
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status = "okay";
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ch0-pin = <45>;
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/* ch0-inverted; */
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};
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```
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The value `ch0-pin` represents the pin that controls the LEDs. With nRF52 boards, you can calculate the value to use in the following way: you need the hardware port and run it through a function.
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**32 \* X + Y** = `<Pin number>` where X is first part of the hardware port "PX.01" and Y is the second part of the hardware port "P1.Y".
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For example, _P1.13_ would give you _32 \* 1 + 13_ = `<45>` and _P0.15_ would give you _32 \* 0 + 15_ = `<15>`.
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If your shield uses a P-channel MOSFET to control backlight instead of a N-channel MOSFET, you may want to enable `ch0-inverted`.
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Then you have to add the following lines inside the root devicetree node on the same file:
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```
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/ {
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backlight: pwmleds {
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compatible = "pwm-leds";
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label = "Backlight LEDs";
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pwm_led_0 {
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pwms = <&pwm0 45>;
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label = "Backlight LED 0";
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};
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};
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};
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```
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The value inside `pwm_led_0` must be the same as you used before.
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:::info
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Note that every LED inside of the backlight node will be treated as a backlight LED, so if you have other PWM LEDs you need to declare them in a separate node. Refer to [Multiple backlight LEDs](#multiple-backlight-leds) if you have multiple backlight LEDs.
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:::
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Finally you need to add backlight to the `chosen` element of the root devicetree node:
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```
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/ {
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chosen {
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zmk,backlight = &backlight;
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};
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}:
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```
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Optionally, on Pro Micro compatible shields you can add a LED GPIO node to your devicetree, this could be useful if you want your shield to be compatible with newer or untested boards. To do that you have to enable `CONFIG_LED_GPIO` in your `.conf` file and then add the following lines inside the root devicetree node of your `.dtsi` or `.dts` file:
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```
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/ {
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backlight: gpioleds {
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compatible = "gpio-leds";
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label = "Backlight LEDs";
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gpio_led_0 {
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gpios = <&pro_micro 20 GPIO_ACTIVE_HIGH>;
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label = "Backlight LED 0";
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};
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};
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};
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```
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If no suitable `<board>.overlay` file is found, this node will act as a fallback, however, without PWM, backlight has limited functionality.
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</TabItem>
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</Tabs>
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### Multiple backlight LEDs
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It is possible to control multiple backlight LEDs at the same time. This is useful if, for example, you have a Caps Lock LED connected to a different pin and you want it to be part of the backlight.
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In order to do that, first you need to enable PWM for each pin:
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```
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&pwm0 {
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status = "okay";
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ch0-pin = <45>; /* LED 0 */
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ch1-pin = <46>; /* LED 1 */
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ch2-pin = <47>; /* LED 2 */
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...
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};
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```
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This part may vary based on your MCU as different MCUs may have a different number of modules and channels.
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Then you can simply add each of your LED to the backlight node:
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```
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backlight: pwmleds {
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compatible = "pwm-leds";
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label = "Backlight LEDs";
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pwm_led_0 {
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pwms = <&pwm0 45>; /* LED 0 */
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};
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pwm_led_1 {
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pwms = <&pwm0 46>; /* LED 1 */
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};
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pwm_led_2 {
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pwms = <&pwm0 47>; /* LED 2 */
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};
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...
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};
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```
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