diff --git a/docs/gpio.md b/docs/gpio.md
index 82f990c..c056604 100644
--- a/docs/gpio.md
+++ b/docs/gpio.md
@@ -1,2 +1,122 @@
+
+## User Accessible GPIOs (J12)
+
+Helios4 provide 12 GPIOs on J12 header that are free to use for user application. This header connected to 16-bit IO Expander [PCA9655E](http://www.onsemi.com/PowerSolutions/product.do?id=PCA9655E) using I2C bus 0.
+
+![J12 Pinout](/img/hardware/gpio_pinout_j12.png)
+
+| Pin | GPIO number | Remarks |
+|------------|----------|---------|
+| 1 |    -   |   3.3V supply  |
+| 2 | IO0_2  |    |
+| 3 | IO0_3  |    |
+| 4 | IO0_4  |    |
+| 5 | IO0_7  |    |
+| 6 | IO1_0  |    |
+| 7 | IO1_1  |    |
+| 8 | IO1_2  |    |
+| 9 | IO1_3  |    |
+| 10 | IO1_4  |    |
+| 11 | IO1_5  |    |
+| 12 | IO1_6  |    |
+| 13 | IO1_7  |    |
+| 14 |   -    | GND |
+
+!!! warning
+    **IO0_0**, **IO0_1**, **IO0_5**, and **IO0_6** are reserved for system use. It is not advisable to access the I2C IO expander directly using I2C.
+
+## LED Expansion (J18)
+
+Helios4 board was designed to either use the on-board LEDs or use custom expansion panel (not-available). To use the header insure to switch to OFF the DIP switch SW2.
+
+![Dipswitch LED](/img/hardware/dipswitch_led_off.png)
+
+- - -
+
+![J18 Pinout](/img/hardware/gpio_pinout_j18.png)
+
+| Pin | LED number | Remarks |
+|------------|----------|---------|
+|  1 |  -   |  3.3V supply  |
+|  2 |  -   |  Not connected |
+|  3 | LED1 | Heartbeat LED  |
+|  4 | LED2 | System Fault LED  |
+|  5 | LED3 | SATA port 1 LED  |
+|  6 | LED4 | SATA port 2 LED  |
+|  7 | LED5 | SATA port 3 LED  |
+|  8 | LED6 | SATA port 4 LED  |
+|  9 | LED7 | USB activity LED  |
+| 10 |  -   | GND |
+
+
+## Accessing GPIOs under Linux
+
+If the kernel support debugfs (*CONFIG_DEBUG_FS=y*), list of GPIOs can be accessed using
+
+`sudo cat /sys/kernel/debug/gpio`
+
+and look for
+
+`gpiochip2: GPIOs XXX-YYY, parent: i2c/0-0020, pca9555, can sleep:`
+
+whereas **XXX** is first GPIO number and **YYY** is last GPIO number of IO expander.
+
+- - -
+
+Another way to get first GPIO number of the IO expander
+
+`cat /sys/bus/i2c/devices/0-0020/gpio/gpiochip*/base`
+
+- - -
+
+** J12 assigned GPIO number in sysfs **
+
+| Pin | Sysfs GPIO number | Remarks |
+|----|-----|---------|
+|  1 |  -  |   3.3V supply  |
+|  2 | 498 |    |
+|  3 | 499 |    |
+|  4 | 500 |    |
+|  5 | 503 |    |
+|  6 | 504 |    |
+|  7 | 505 |    |
+|  8 | 506 |    |
+|  9 | 507 |    |
+| 10 | 508 |    |
+| 11 | 509 |    |
+| 12 | 510 |    |
+| 13 | 511 |    |
+| 14 |  -  |  GND |
+
 !!! info
-    Coming soon.
+    The GPIO number listed on the table most likely would not changed between kernel version.
+
+
+Declare GPIO number to be use.
+
+`echo N | sudo tee -a /sys/class/gpio/export`
+
+Set the direction, "out" as output and "in" as "input".
+
+`echo DIRECTION | sudo tee -a /sys/class/gpio/gpioN/direction`
+
+To read current GPIO input
+
+`cat /sys/class/gpio/gpioN/value`
+
+Write 0 or 1 to GPIO
+
+`echo VALUE | sudo tee -a /sys/class/gpio/gpioN/value`
+
+!!! notes
+    Pay attention to the path, /sys/class/gpio/gpio**N**/
+
+### Example
+
+Set IO1_7 (pin 13) output as high
+
+```
+echo 511 | sudo tee -a /sys/class/gpio/export
+echo "out" | sudo tee -a /sys/class/gpio/gpio511/direction
+echo 1 | sudo tee -a /sys/class/gpio/gpio511/value
+```
diff --git a/docs/hardware.md b/docs/hardware.md
index 2ea571f..97c1ba7 100644
--- a/docs/hardware.md
+++ b/docs/hardware.md
@@ -60,7 +60,7 @@ LED8|green|Power indicator
 
 Helios4 board was designed to either use the on-board LEDs or use an expansion panel (not-available). To use the on-board LEDs insure to switch to ON the dipswitch SW2.
 
-![Dipswitch LED](/img/hardware/dipswitch_led.jpg)
+![Dipswitch LED](/img/hardware/dipswitch_led_on.jpg)
 
 ## Reset Button
 
diff --git a/docs/img/hardware/dipswitch_led_off.png b/docs/img/hardware/dipswitch_led_off.png
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diff --git a/docs/img/hardware/dipswitch_led.jpg b/docs/img/hardware/dipswitch_led_on.jpg
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rename from docs/img/hardware/dipswitch_led.jpg
rename to docs/img/hardware/dipswitch_led_on.jpg
diff --git a/docs/img/hardware/gpio_pinout_j12.png b/docs/img/hardware/gpio_pinout_j12.png
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diff --git a/docs/img/hardware/gpio_pinout_j18.png b/docs/img/hardware/gpio_pinout_j18.png
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