.. BeagleBoard projects Blink LED demo .. _blinkLED: Blink an LED ############ The "Hello World!" of the embedded world is to blink an LED. Here we'll show you how to do just that in three simple steps. #. Plug in the Beagle #. Log into the Beagle #. Blink the LED These steps will work for any of the Beagles. Plug in the Beagle ******************* For this step you need to get a USB cable and attach your Beagle to your host computer with it. Where you attached the cable depends on which Beagle you have. Click on the tab for your board. .. tab-set:: .. tab-item:: Black .. figure:: figures/image8.jpg :width: 632px :align: center :alt: Tethered Configuration Tethered Configuration .. figure:: figures/image9.jpg :width: 451px :align: center :alt: USB Connection to the Board Mini USB Connection to the Board as seen from the bottom. For more details see: :ref:`beagleboneblack-connectivity` .. tab-item:: Blue .. figure:: figures/blueconnect.jpg :width: 451px :align: center :alt: USB Connection to the Blue Micro USB Connection to the Blue .. tab-item:: AI-64 .. figure:: figures/usb-tethering.jpg :width: 400px :align: center :alt: Tethered Configuration Tethered Configuration .. figure:: figures/usb-c-connection.jpg :width: 400px :align: center :alt: USB Connection to the Board USB-c Connection to the Board .. figure:: figures/usb-a-connection.jpg :width: 400px :align: center :alt: USB Connection to the PC/Laptop USB Connection to the PC/Laptop .. figure:: figures/power-led.jpg :width: 400px :align: center :alt: Board Power LED Board Power LED For more details see: :ref:`bbai64-quick-start` .. tab-item:: Play .. figure:: figures/tethered-connection.jpg :width: 1400 :align: center :alt: Tethering BeaglePlay to PC Tethering BeaglePlay to PC For more details see: :ref:`beagleplay-quick-start` .. tab-item:: Pocket .. figure:: figures/11fig-PB-microUSBattach1.jpg :align: center :alt: Tethered Configuration Micro USB Connection For more details see: :REF:`connecting_up_pocketbeagle` Once attached you will see some LEDs blinking. Wait a bit and the blinking will settle down to a steady heart beat. The Beagle is now up and running, but you didn't have to load up Linux. This is because all Beagles (except PocketBeagle, see :ref:`flash-latest-image` to install an image on the Pocket) have built-in flash memory that has the Debian distribution of Linux preinstalled. .. _intro-using-vs-code: Using VS Code ************** .. important:: If VS code is not installed on your board please skip this section and refer to next section on how to login and run the code via command line. Recent Beagles come with the IDE Visual Studio Code (https://code.visualstudio.com/) installed and running. To access it, open a web browser on your host computer and browse to: ``192.168.7.2:3000`` (use ``192.168.6.2:3000`` for the Mac) and you will see something like: .. figure:: figures/vscode1.png :width: 740 :align: center At this point you can either run the scripts via a command line within VS Code, or run them by clicking the ``RUN Code`` button. Running via the command line ============================ Open a terminal window in VS Code by dropping down the ``Terminal`` menu and selecting ``New Terminal`` (or entering ``Ctrl+```). The terminal window appears at the bottom of the screen as shown below. .. figure:: figures/vscode3.png :width: 740 :align: center You can now enter commands and see them run as shown below. .. figure:: figures/vscode4.png :width: 740 :align: center Running via the ``RUN`` button =============================== Use the file navigator on the left to navigate to ``examples/BeagleBone/Black/blinkInternalLED.sh`` and you will see: .. figure:: figures/vscode2.png :width: 740 :align: center This code blinks one of the USR LEDs built into the board. Click on the ``RUN Code`` triangle on the upper right of the screen (see red arrow) to run the code. (You could also enter ``Ctrl+Alt+N``) The USR3 LED should now be blinking. Click on the ``Stop Code Run`` (``Ctrl+Alt+M``) square to the right of the ``Run Code`` button. Time to play! Try changing the LED number (on line 10) from 3 to something else. Click the ``Run Code`` button (no need to save the file, autosave is on by default). Try running ``seqLEDs.py``. Using command line ****************** To access the command line and your host is a Mac, take the ``ssh (Mac)`` tab. If you are running Linux on your host, take the ``ssh (Linux)`` tab. Finally take the ``putty (Windows)`` tab for command line from Windows. .. tab-set:: .. tab-item:: ssh (Mac) If you are running a Mac host, open a terminal widow and run .. code-block:: shell-session host:~$ ssh debian@192.168.6.2 Use the password ``temppwd``. .. tab-item:: ssh (Linux) If you are running a Linux host, open a terminal widow and run .. code-block:: shell-session host:~$ ssh debian@192.168.7.2 Use the password ``temppwd``. .. tab-item:: putty (Windows) If you are running Window you need to run an ``ssh`` client to connect to the Beagle. I suggest you use ``putty``. You can download it here: https://www.putty.org/. Once installed, launch it and connect to your Beagle by sshing to ``192.168.7.2``. .. figure:: figures/putty.png Login with user ``debian`` and password ``temppwd``. Blink an LED ============ Once logged in the rest is easy. First: .. code-block:: shell-session bone:~$ cd ~/examples/BeagleBone/Black bone:~$ ls README.md blinkInternalLED.sh blinkLED2.py input2.js analogIn.py blinkLED.bs.js blinkLEDold.py seqLEDs.py analogInCallback.js blinkLED.c fadeLED.js swipeLED.js analogInContinuous.py blinkLED.js fadeLED.py analogInOut.js blinkLED.py gpiod analogInSync.js blinkLED.sh input.js Here you see a list of many scripts that demo simple input/output on the Beagle. Try one that works on the internal LEDs. .. code-block:: shell-session bone:~$ cat blinkInternalLED.py LED="3" LEDPATH='/sys/class/leds/beaglebone:green:usr' while true ; do echo "1" > ${LEDPATH}${LED}/brightness sleep 0.5 echo "0" > ${LEDPATH}${LED}/brightness sleep 0.5 done bone:~$ ./blinkInternalLED.py ^c Here you see a simple bash script that turns an LED on and off. Enter Ctrl+c to stop the script. Blinking via Python ==================== Here's a script that sequences the LEDs on and off. .. code-block:: shell-session bone:~$ cat seqLEDs.py import time import os LEDs=4 LEDPATH='/sys/class/leds/beaglebone:green:usr' # Open a file for each LED f = [] for i in range(LEDs): f.append(open(LEDPATH+str(i)+"/brightness", "w")) # Sequence while True: for i in range(LEDs): f[i].seek(0) f[i].write("1") time.sleep(0.25) for i in range(LEDs): f[i].seek(0) f[i].write("0") time.sleep(0.25) bone:~$ ./seqLEDs.py ^c Again, hit Ctrl+c to stop the script. Blinking from Command Line ========================== You can control the LEDs from the command line. .. code-block:: shell-session bone:~$ cd /sys/class/leds bone:~$ ls beaglebone:green:usr0 beaglebone:green:usr2 mmc0:: beaglebone:green:usr1 beaglebone:green:usr3 mmc1:: Here you see a list of LEDs. Your list may be slightly different depending on which Beagle you are running. You can blink any of them. Let's try ``usr1``. .. code-block:: shell-session bone:~$ cd beaglebone\:green\:usr1/ bone:~$ ls brightness device max_brightness power subsystem trigger uevent bone:~$ echo 1 > brightness bone:~$ echo 0 > brightness When you echo 1 into ``brightness`` the LED turns on. Echoing a 0 turns it off. Blinking other LEDs =================== You can blink the other LEDs by changing in to thier directories and doing the same. Let's blink the USR0 LED. .. code-block:: shell-session bone:~$ cd ../beaglebone\:green\:usr0/ bone:~$ echo 1 > brightness bone:~$ echo 0 > brightness Did you notice that LED ``usr0`` blinks on it's own in a heartbeat pattern? You can set an LED trigger. Here's what triggers you can set: .. code-block:: shell-session bone:~$ cat trigger none usb-gadget usb-host rfkill-any rfkill-none kbd-scrolllock kbd-numlock kbd-capslock kbd-kanalock kbd-shiftlock kbd-altgrlock kbd-ctrllock kbd-altlock kbd-shiftllock kbd-shiftrlock kbd-ctrlllock kbd-ctrlrlock timer oneshot disk-activity disk-read disk-write i de-disk mtd nand-disk [heartbeat] backlight gpio c pu cpu0 cpu1 cpu2 cpu3 activity default-on panic netdev mmc0 mmc1 mmc2 phy0rx phy0tx phy0assoc phy0radio rfkill0 gpio-0:00:link gpio-0:00:1Gbps gpio-0:00:100Mbps gpio-0:00:10Mbps gpio-0:01:link gpio-0:01:10Mbps bone:~$ echo none > trigger Notice ``[heartbeat]`` is in brackets. This shows it's the current trigger. The echo changes the trigger to ``none``. Try experimenting with some of the other triggers and see if you can figure them out. Another way to Blink an LED =========================== An interesting thing about Linux is there are often many ways to do the same thing. For example, I can think of at least five ways to blink an LED. Here's another way using the ``gpiod`` system. First see where the LEDs are attached. .. code-block:: shell-session bone:~$ gpioinfo | grep -e chip -ie usr gpiochip0 - 32 lines: gpiochip1 - 32 lines: line 21: "[usr0 led]" "beaglebone:green:usr0" output active-high [used] line 22: "[usr1 led]" "beaglebone:green:usr1" output active-high [used] line 23: "[usr2 led]" "beaglebone:green:usr2" output active-high [used] line 24: "[usr3 led]" "beaglebone:green:usr3" output active-high [used] gpiochip2 - 32 lines: gpiochip3 - 32 lines: Here we asked how the LEDs are attached to the General Purpose IO (gpio) system. The answer is, (yours will be different for a different Beagle) there are four interface chips and the LEDs are attached to chip 1. You can control the gpios (and thus the LEDs) using the ``gpioset`` command. .. code-block:: shell-session bone:~$ gpioset --mode=time --sec=2 1 22=1 bone:~$ gpioset --mode=time --sec=2 1 22=0 The first command sets chip 1, line 22 (the usr1 LED) to 1 (on) for 2 seconds. The second command turns it off for 2 seconds. Try it for the other LEDs. .. note:: This may not work on all Beagles since it depends on which version of Debian you are running. Blinking in response to a button ================================= Some Beagles have a USR button that can be used to control the LEDs. You can test the USR button with ``evtest`` .. code-block:: shell-session bone:~$ evtest No device specified, trying to scan all of /dev/input/event* Not running as root, no devices may be available. Available devices: /dev/input/event0: tps65219-pwrbutton /dev/input/event1: gpio-keys Select the device event number [0-1]: 1 We want to use ``gpio-keys``, so enter ``1``. Press and release the USR button and you'll see: .. code-block:: shell-session Input driver version is 1.0.1 Input device ID: bus 0x19 vendor 0x1 product 0x1 version 0x100 Input device name: "gpio-keys" Supported events: Event type 0 (EV_SYN) Event type 1 (EV_KEY) Event code 256 (BTN_0) Key repeat handling: Repeat type 20 (EV_REP) Repeat code 0 (REP_DELAY) Value 250 Repeat code 1 (REP_PERIOD) Value 33 Properties: Testing ... (interrupt to exit) Event: time 1692994988.305846, type 1 (EV_KEY), code 256 (BTN_0), value 1 Event: time 1692994988.305846, -------------- SYN_REPORT ------------ Event: time 1692994988.561786, type 1 (EV_KEY), code 256 (BTN_0), value 2 Event: time 1692994988.561786, -------------- SYN_REPORT ------------ Event: time 1692994988.601883, type 1 (EV_KEY), code 256 (BTN_0), value 2 Event: time 1692994988.601883, -------------- SYN_REPORT ------------ Event: time 1692994988.641754, type 1 (EV_KEY), code 256 (BTN_0), value 2 Event: time 1692994988.641754, -------------- SYN_REPORT ------------ Event: time 1692994988.641754, type 1 (EV_KEY), code 256 (BTN_0), value 0 Event: time 1692994988.641754, -------------- SYN_REPORT ------------ Ctrl+c The following script uses evtest to wait for the USR button to be pressed and then turns on the LED. .. literalinclude:: code/buttonEvent.sh :language: Shell :caption: buttonEvent.sh :linenos: :download:`code/buttonEvent.sh` Try running it and pressing the USR button. The next script polls the USR button and toggles the LED. .. literalinclude:: code/buttonLED.sh :language: shell :caption: buttonLED.sh :linenos: :download:`code/buttonLED.sh`