PWM (Onboard RGB LED)

Controlling PWM on NavQ

The PWM chips are tied to the onboard LED on NavQ. There are three PWM chips: pwmchip0, pwmchip1, and pwmchip2. Each of these "chips" have one PWM line attached to them: pwm0. To use these PWM lines, you will need to use the sysfs interface.

Using the sysfs interface to control the onboard LED

Step 1

Log into the root user on NavQ by running this command:

$ sudo su -
<enter password>

Step 2

Navigate to /sys/class/pwm and run the following commands:

$ echo 0 > pwmchip0/export
$ echo 0 > pwmchip1/export
$ echo 0 > pwmchip2/export

Step 3

Now that our PWM lines are exported for each chip, we can change the duty cycle of the PWM lines and enable them. The default frequency is 2730667 Hz. For a 50% duty cycle, we will use half of this number: 1365333. Apply this duty cycle to each chip by running the following commands:

$ echo 1365333 > pwmchip0/pwm0/duty_cycle
$ echo 1365333 > pwmchip1/pwm0/duty_cycle
$ echo 1365333 > pwmchip2/pwm0/duty_cycle

Step 4

We will now enable each line. The colors for each chip are as follows:

pwmchip0: RED

pwmchip1: GREEN

pwmchip2: BLUE

To enable the colors, run the following commands:

$ echo 1 > pwmchip0/pwm0/enable
$ echo 1 > pwmchip1/pwm0/enable
$ echo 1 > pwmchip2/pwm0/enable

Running these commands in succession should enable the LEDs in a RED, GREEN, BLUE pattern until you reach a white LED.

Controlling the onboard LEDs programmatically