LED location

On-Board LEDs

LED number Color Software control Remarks
LED1 Green Yes Active-low
LED2 Red Yes Active-low
LED3 Green Yes Active-low
LED4 Green Yes Active-low
LED5 Green Yes Active-low
LED6 Green Yes Active-low
LED7 Green Yes Active-low
LED8 Green No Power indicator


LED1 - LED7 is preconfigured for certain indicator under Linux, see LED under Linux section.

Expansion Panel (J18)

Helios4 board was designed to either use the on-board LEDs or use a custom expansion panel (not-available). If you wish to use the header, insure to switch to OFF the Dip Switch SW2.

Dipswitch LED

Pinout Table

J18 Pinout

Pin LED number Remarks
1 - 3.3V supply
2 - Not connected
3 LED1 Active-low
4 LED2 Active-low
5 LED3 Active-low
6 LED4 Active-low
7 LED5 Active-low
8 LED6 Active-low
9 LED7 Active-low
10 - GND


LED1 - LED7 is preconfigured for certain indicator under Linux, see LED under Linux section.

Wiring Diagram

Since the signals to control the LEDs are active low, connect the pin to LED's cathode. Below a wiring diagram example.

Wiring Example

LED under Linux

LED Name Default Trigger Remarks
LED1 helios4:green:status heartbeat Blinking periodically
LED2 helios4:red:fault none See Configuring Fault LED
LED3 helios4:green:ata1 ata1 Blinking on SATA1 activity
LED4 helios4:green:ata2 ata2 Blinking on SATA2 activity
LED5 helios4:green:ata3 ata3 Blinking on SATA3 activity
LED6 helios4:green:ata4 ata4 Blinking on SATA4 activity
LED7 helios4:green:usb usb-host Blinking on USB activity, any port


ata trigger requires additional patch to mainline kernel. The patch can be found here. Armbian builds are already patched, so no action is required.

The LEDs can be accessed under LEDs class in sysfs.

root@helios4:~/# ls -l /sys/class/leds/

lrwxrwxrwx 1 root root 0 Dec  4 06:57 helios4:green:ata1 -> ../../devices/platform/io-leds/leds/helios4:green:ata1
lrwxrwxrwx 1 root root 0 Dec  4 06:57 helios4:green:ata2 -> ../../devices/platform/io-leds/leds/helios4:green:ata2
lrwxrwxrwx 1 root root 0 Dec  4 06:57 helios4:green:ata3 -> ../../devices/platform/io-leds/leds/helios4:green:ata3
lrwxrwxrwx 1 root root 0 Dec  4 06:57 helios4:green:ata4 -> ../../devices/platform/io-leds/leds/helios4:green:ata4
lrwxrwxrwx 1 root root 0 Dec  4 06:57 helios4:green:status -> ../../devices/platform/system-leds/leds/helios4:green:status
lrwxrwxrwx 1 root root 0 Dec  4 06:57 helios4:green:usb -> ../../devices/platform/io-leds/leds/helios4:green:usb
lrwxrwxrwx 1 root root 0 Dec  4 06:57 helios4:red:fault -> ../../devices/platform/system-leds/leds/helios4:red:fault

LEDs Trigger

  • none

No automatic trigger. Manually control the LED by manipulating "brightness". More info see Configuring LED trigger.

  • heartbeat

LED "double" flashes at a load average based rate. The interval might change during heavy load. If the LED no longer blinks, it means the system is locked-up or hung and has to be reset.

  • ataN

LED blinks on any read/write activity at specific SATA port.

  • usb-host

LED blinks on USB activity at any port.

  • panic

This trigger allows LEDs to be configured to blink on a kernel panic.

  • timer

This allows LEDs to be controlled by a programmable timer via sysfs. delay_on to set how long the LED turned on and delay_off to set how long the LED turned off.

Configuring LED trigger

To configure, simply set the trigger type. For example to set Status LED triggered by timer

echo timer | sudo tee -a  /sys/class/leds/helios4\:green\:status/trigger

Some of the triggers may expose additional parameters that can be configured further.

On none trigger, to turn ON the LED set the brightness bigger than 0.

echo 1 | sudo tee -a  /sys/class/leds/helios4\:green\:status/brightness

and to turn OFF the LED set the brightness to 0.

echo 0 | sudo tee -a  /sys/class/leds/helios4\:green\:status/brightness

On timer trigger, it will exposed delay_on and delay_off with default value of 0.5 seconds for both. To change the delay, set the respective parameter (value in milliseconds)

echo 1000 | sudo tee -a  /sys/class/leds/helios4\:green\:status/delay_on
echo 200 | sudo tee -a  /sys/class/leds/helios4\:green\:status/delay_off


The changes is not retained across reboot. Use startup script or udev rules to make it permanent.

Configuring Fault LED

While other LEDs are preconfigured, the fault LED remains unconfigured (trigger:none).

1. As Kernel Panic Indicator

To configure the LED as Kernel panic indicator, set the trigger to panic. However this functionality might be redundant with Status LED, since if a kernel panic occurs and/or system hangs, the Status LED will no longer blink.

To trigger kernel panic to test the LED, run

echo c > /proc/sysrq-trigger


Triggering kernel panic can lead to data loss. Use with caution!

2. As RAID Fault Indicator

To configure the LED as RAID fault indicator, please refer to MDADM: Configure Fault LED


On Armbian builds, this is the default setting for fault LED.