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feature_led_indicators.md

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LED Indicators

?> Currently, this feature is not supported for split keyboards

QMK provides methods to read 5 of the LEDs defined in the HID spec:

  • Num Lock
  • Caps Lock
  • Scroll Lock
  • Compose
  • Kana

There are three ways to get the lock LED state:

  • by specifying configuration options within config.h
  • by implementing bool led_update_kb(led_t led_state) or _user(led_t led_state); or
  • by calling led_t host_keyboard_led_state()

!> host_keyboard_led_state() may already reflect a new value before led_update_user() is called.

Two more deprecated functions exist that provide the LED state as a uint8_t:

  • uint8_t led_set_kb(uint8_t usb_led) and _user(uint8_t usb_led)
  • uint8_t host_keyboard_leds()

Configuration Options

To configure the indicators, #define these in your config.h:

Define Default Description
LED_NUM_LOCK_PIN Not defined The pin that controls the Num Lock LED
LED_CAPS_LOCK_PIN Not defined The pin that controls the Caps Lock LED
LED_SCROLL_LOCK_PIN Not defined The pin that controls the Scroll Lock LED
LED_COMPOSE_PIN Not defined The pin that controls the Compose LED
LED_KANA_PIN Not defined The pin that controls the Kana LED
LED_PIN_ON_STATE 1 The state of the indicator pins when the LED is "on" - 1 for high, 0 for low

Unless you are designing your own keyboard, you generally should not need to change the above config options.

led_update_*()

When the configuration options do not provide enough flexibility, the API hooks provided allow custom control of the LED behavior. These functions will be called when the state of one of those 5 LEDs changes. It receives the LED state as a struct parameter.

By convention, return true from led_update_user() to get the led_update_kb() hook to run its code, and return false when you would prefer not to run the code in led_update_kb().

Some examples include:

  • overriding the LEDs to use them for something else like layer indication
    • return false because you do not want the _kb() function to run, as it would override your layer behavior.
  • play a sound when an LED turns on or off.
    • return true because you want the _kb function to run, and this is in addition to the default LED behavior.

?> Because the led_set_* functions return void instead of bool, they do not allow for overriding the keyboard LED control, and thus it's recommended to use led_update_* instead.

Example led_update_kb() Implementation

bool led_update_kb(led_t led_state) {
    bool res = led_update_user(led_state);
    if(res) {
        // writePin sets the pin high for 1 and low for 0.
        // In this example the pins are inverted, setting
        // it low/0 turns it on, and high/1 turns the LED off.
        // This behavior depends on whether the LED is between the pin
        // and VCC or the pin and GND.
        writePin(B0, !led_state.num_lock);
        writePin(B1, !led_state.caps_lock);
        writePin(B2, !led_state.scroll_lock);
        writePin(B3, !led_state.compose);
        writePin(B4, !led_state.kana);
    }
    return res;
}

Example led_update_user() Implementation

This incomplete example would play a sound if Caps Lock is turned on or off. It returns true, because you also want the LEDs to maintain their state.

#ifdef AUDIO_ENABLE
  float caps_on[][2] = SONG(CAPS_LOCK_ON_SOUND);
  float caps_off[][2] = SONG(CAPS_LOCK_OFF_SOUND);
#endif

bool led_update_user(led_t led_state) {
    #ifdef AUDIO_ENABLE
    static uint8_t caps_state = 0;
    if (caps_state != led_state.caps_lock) {
        led_state.caps_lock ? PLAY_SONG(caps_on) : PLAY_SONG(caps_off);
        caps_state = led_state.caps_lock;
    }
    #endif
    return true;
}

led_update_* Function Documentation

  • Keyboard/Revision: bool led_update_kb(led_t led_state)
  • Keymap: bool led_update_user(led_t led_state)

host_keyboard_led_state()

Call this function to get the last received LED state as a led_t. This is useful for reading the LED state outside led_update_*, e.g. in matrix_scan_user().

Setting Physical LED State

Some keyboard implementations provide convenience methods for setting the state of the physical LEDs.

Ergodox Boards

The Ergodox implementations provide ergodox_right_led_1/2/3_on/off() to turn individual LEDs on or off, as well as ergodox_right_led_on/off(uint8_t led) to turn them on or off by their index.

In addition, it is possible to specify the brightness level of all LEDs with ergodox_led_all_set(uint8_t n); of individual LEDs with ergodox_right_led_1/2/3_set(uint8_t n); or by index with ergodox_right_led_set(uint8_t led, uint8_t n).

Ergodox boards also define LED_BRIGHTNESS_LO for the lowest brightness and LED_BRIGHTNESS_HI for the highest brightness (which is the default).