AP_Scripting: add an applet to control LED brightness with a switch

libraries/AP_Scripting/applets/leds_on_a_switch.lua

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+-- leds_on_a_switch.lua: control led brightness with a radio switch
+--
+
+-- constants
+local AuxSwitchPos = {LOW=0, MIDDLE=1, HIGH=2}
+local NTF_LED_BRIGHT = Parameter("NTF_LED_BRIGHT")
+local MAV_SEVERITY = {EMERGENCY=0, ALERT=1, CRITICAL=2, ERROR=3, WARNING=4, NOTICE=5, INFO=6, DEBUG=7}
+
+-- state
+local prev_pos = -1
+
+function update()
+    local sw_pos = rc:get_aux_cached(300)
+    if sw_pos ~= prev_pos then
+        if sw_pos == AuxSwitchPos.LOW then
+            NTF_LED_BRIGHT:set(0)
+            gcs:send_text(MAV_SEVERITY.INFO, "LEDs turned OFF")
+        elseif sw_pos == AuxSwitchPos.MIDDLE then
+            NTF_LED_BRIGHT:set(1)
+            gcs:send_text(MAV_SEVERITY.INFO, "LEDs dimmed")
+        else
+            NTF_LED_BRIGHT:set(3)
+            gcs:send_text(MAV_SEVERITY.INFO, "LEDs turned ON")
+        end
+        prev_pos = sw_pos
+    end
+    return update, 1000
+end
+
+return update, 5000

libraries/AP_Scripting/applets/leds_on_a_switch.md

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+# `leds_on_a_switch.lua`: change LED brightness using an RC switch
+
+ArduPilot controls LED brightness via the parameter `NTF_LED_BRIGHT`. This script allows you to control the value of the parameter using an RC switch.
+
+Configure an `RCx_OPTION` as 300 for scripting and load this script.
+The low position will turn off the LEDs, the high position with give maximum brightness and the middle position will dim the LEDs