Using the LEDs - dlech/ev3dev GitHub Wiki

NOTE: This documentation applies to kernel version 3.16.1-ev3dev or newer.

NOTE: You you must be a member of the ev3dev group (or root) to be able to control the LEDs.

When the EV3 is booting, the LEDs flash amber (orange). When it is finished booting, they turn solid green.

The LEDs live in /sys/class/leds.

$ ls /sys/class/leds/
ev3:green:left  ev3:green:right  ev3:red:left  ev3:red:right

You probably noticed that amber is missing here. We will get to that in a bit.

Each LED has it's own attributes for controlling it. We are using the standard Linux LED device class, so there is a bunch of extra stuff that it not really useful. Let's figure out what is...

$ ls /sys/class/leds/ev3\:green\:left/
brightness  device  max_brightness  power subsystem  trigger  uevent

NOTE: You only have to escape the colons when using shell. The real directory name is ev3:green:left.

# turn the left green LED off
$ echo 0 > /sys/class/leds/ev3\:green\:left/brightness
# find out what the maximum brightness value is
$ cat /sys/class/leds/ev3\:green\:left/max_brightness
255
# turn the left green LED back on
$ echo 255 > /sys/class/leds/ev3\:green\:left/brightness
# dim the left green LED 1/2 way
$ echo 127 > /sys/class/leds/ev3\:green\:left/brightness

Triggers can make the LED do interesting things.

$ cat /sys/class/leds/ev3\:green\:left/trigger
[none] mmc0 timer heartbeat default-on transient legoev3-battery-charging-or-full legoev3-battery-charging legoev3-battery-full legoev3-battery-charging-blink-full-solid rfkill0

• none means we are manually controlling the LED with brightness like we just did.

• mmc0 makes the LED blink whenever there is SD card activity. This is what the right LED was doing during boot.

• timer makes the LED blink. When we change the trigger, we get new attributes for controlling the on and off times. Times are in milliseconds.

  $ echo timer > /sys/class/leds/ev3\:green\:left/trigger
  $ ls/sys/class/leds/ev3\:green\:left/
  brightness  delay_on  max_brightness  subsystem  uevent
  delay_off   device    power	      trigger
  $ cat /sys/class/leds/ev3\:green\:left/delay_on
  500
  $ echo 1000 > /sys/class/leds/ev3\:green\:left/delay_on
  $ echo 2000 > /sys/class/leds/ev3\:green\:left/delay_off
  

• heartbeat makes the LED blink at a rate proportional to CPU usage. This is what the left LED was doing during boot.

• default-on works just like none except that it turns the LED on when the trigger is set.

• legoev3-battery-* are not useful. The batteries (including the rechargeable battery pack) do not have a way of telling the EV3 what is going on, so it is assumed that the batteries are always discharging. Therefore these triggers will always turn the LED off.

• rfkill0 is the RF (radio frequency) kill switch for the built-in Bluetooth. It should make the LED indicate if the built-in Bluetooth is turned on or not.

To make the LED amber, we just have to turn on both the red and green LEDs at the same time.

# make left LED illuminate amber
$ echo 255 > /sys/class/leds/ev3\:green\:left/brightness; echo 255 > /sys/class/leds/ev3\:red\:left/brightness
# turn off left LED
$ echo 0 > /sys/class/leds/ev3\:green\:left/brightness; echo 0 > /sys/class/leds/ev3\:red\:left/brightness

How does red + green make amber? If you open up your favorite paint program that has a color chooser where you can adjust the individual red, green and blue values, we can see what is going on. Make sure blue is on zero, then change red and green both to their maximum values. You get yellow. On the EV3, the red LED is a bit stronger than than the green LED, so both LEDs at max brightness appears orange (which we are calling amber just because it is "supposed" to be sort of yellow-ish). In your paint program, if you leave red at the maximum value and start decreasing green, the color will start to turn orange and then red. So, playing around with the brightness values a bit, we can actually get orange and yellow.

# make the left LED really orange
$ echo 180 > /sys/class/leds/ev3\:green\:left/brightness; echo 255 > /sys/class/leds/ev3\:red\:left/brightness
# make the left LED yellow (this shows us how much stronger the red led is!)
$ echo 255 > /sys/class/leds/ev3\:green\:left/brightness; echo 25 > /sys/class/leds/ev3\:red\:left/brightness