zephyr/samples/basic/blink_led

.. _blink-led-sample:

PWM: Blink LED
##############

Overview
********

This is a sample app which blinks a LED using PWM.

The LED will start at a blinking frequency of 1 Hz. Every 4 seconds,
the blinking frequency will double. When the blinking frequency
reaches 64 Hz, the blinking frequency will be halved every 4 seconds
until the blinking frequency reaches 1 Hz. This completes a whole
blinking cycle. This faster-then-slower LED blinking cycle repeats forever.

Since for some PWM hardware it might be not possible to set the PWM period of
1 second (to achieve the blinking frequency of 1 Hz), this application at its
beginning tries to determine what is available for the used PWM hardware,
and accordingly decreases the maximum PWM period (thus increases the initial
blinking frequency) if needed.


Wiring
******

Nucleo_F401RE, Nucleo_L476RG, STM32F4_DISCOVERY, Nucleo_F302R8
==============================================================
Connect PWM2(PA0) to LED

Nucleo_F103RB
=============
Connect PWM1(PA8) to LED

Nucleo_L496ZG
=============
No special board setup is necessary because there are three on-board LEDs (red,
green, blue) connected to the Nucleo's PWM.

Hexiwear K64
============
No special board setup is necessary because there is an on-board RGB LED
connected to the K64 PWM.

nrf52840dk_nrf52840
===================
No special board setup is necessary because there is an on-board LED connected.

Building and Running
********************

This sample can be built for multiple boards, in this example we will build it
for the nrf52840dk_nrf52840 board:

.. zephyr-app-commands::
   :zephyr-app: samples/basic/blink_led
   :board: nrf52840dk_nrf52840
   :goals: build flash
   :compact:

After flashing the image to the board, the user LED on the board should start to
blinking as discussed in overview