qmk_firmware/keyboards/playkbtw/ca66/ca66.c

#include "ca66.h"

void led_set_kb(uint8_t usb_led) {
	// put your keyboard LED indicator (ex: Caps Lock LED) toggling code here
  if (IS_LED_ON(usb_led, USB_LED_CAPS_LOCK)) {
    writePinHigh(D1);
  } else {
    writePinLow(D1);
  }

	led_set_user(usb_led);
}