EBC Exercises on BBB - Control LED

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Using Sysfs

The easiest way to do general purpose I/O(gpio) on BBB is through the terminal and shell command. sysfs is the virtual file system which exposes the drivers for the hardware so you can directly use them.

# cd /sys/class/leds
# ls
# beaglebone:green:usr0  beaglebone:green:usr1  beaglebone:green:usr2  beaglebone:green:usr3
# cd beaglebone\:green\:usr0
# cat trigger 
none nand-disk mmc0 mmc1 timer oneshot [heartbeat] backlight gpio cpu0 default-on transient 

If you want to disable the heartbeat:

# echo none > trigger
# cat trigger 
[none] nand-disk mmc0 mmc1 timer oneshot heartbeat backlight gpio cpu0 default-on transient 

Turn on/off the led via:

# echo 1 > brightness
# echo 0 > brightness

More trigger options via:

# echo timer>trigger 
# cat trigger 
none nand-disk mmc0 mmc1 [timer] oneshot heartbeat backlight gpio cpu0 default-on transient 

Set the deplay frequency:

echo 100>delay_on
echo 900>delay_off

Adding Own LED

Add the connection of LED.
P9 Pin1 –> 220 ohm –> LED Negative Pin P9 Pin 12 -> Led Positive Pin

Pin 12 in the table is shown in table as GPIO1_28. Bank of 32 each, so find the gpio number via:
1*32+28=60.

We have to turn this pin on.

Turn it ON

export/unexport, turn on/off of the LED via following command:

$ cd /sys/class/gpio/
$ echo 60 > export
$ cd gpio60/
$ echo out > direction
$ echo 1 > value
$ echo 0 > value
$ cd ..
$ ls
export  gpio60  gpiochip0  gpiochip32  gpiochip64  gpiochip96  unexport
$ echo 60 > unexport
$ ls -F
export  gpiochip0@  gpiochip32@  gpiochip64@  gpiochip96@  unexport

Add Own Key

Connection for the key:
P9 Pin 3(3.3V) –>220 ohm –> Key 1
P9 Pin 42 –> Key 2
Pin 42 is GPIO0_7, then the actual gpio number is Just 7.

Read Value

export/unexport, read value via following command:

# cd /sys/class/gpio/
# echo 7 > export
# cd gpio7/
# echo in > direction
# cat value
# cat value 
0
Hold down the button and see the result: 
# cat value 
1

The script for reading the gpio value:

# ./readgpio.sh 7
sh: echo: I/O error
trap: SIGINT: bad trap
__________________________|^^^^^^^^^^^^^^^^^^^^^^^|__________|^^^^^^^^^^|___
___|^^^^^^^|______|^^^^^^^|______|^^^^^^^|______|^^^^^^^|______|^^^^^^^|______|^^^^
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^|____|^^^^^^^^|____|^^|__|^^|_|^^^^^^|___|^^
|__|^|__|^|__|^|__|^^|___|^|_|^|___|^|_|^|_|^|_|^^|_|^|_|^|_|^^|_|^^^^^^^^^^^^^|______|^^^^^^^^^^^^^^^
^^^^^^^^^^^^^^^^^^^^^^^^|____|^^^^^^^^^^^|_____|^^^^^^^^^^^^^^|____|^^^^^^^^^^
^^^|___|^^^^^^^^^^^^|____|^^^^^^^^^^^^|__|^^^^^^^^^^|__|^^^^^^^^|__|^^^^^^^|___|^^^^
^|_____|^^^^^|____|^^^^^^^^^^^^^^^^^^^^^^^|___|^^^^^^^^^^^^^^^^^|___|^^^^^^^^^^^
|_^C

This seems like a little game.