LED Fade

The following page provides an example of fading an LED in and out.

Background

To modify the brightness of an LED, we utilise Pulse-Width-Modulation (PWM) - modifying the duty cycle of a square wave to control its average supply power.

Example

As usual, first the required functions from the API are imported.

LUA

import("reset_all_io_type_cfg")
import("set_io_type_cfg")
import("set_pwm")
import("set_gpio")
import("msleep_f")

Next (again, as usual) set the I/O to the desired type:

LUA

PWM_PIN = 1
LOOP_COUNT = 10

reset_all_io_type_cfg()
set_io_type_cfg(PWM_PIN, PWM)
set_io_type_cfg(PIN2, GPIO_OUT)
set_io_type_cfg(PIN3, GPIO_OUT)

A helper function, which returns true if the number argument passed to it is even (false otherwise), is added to simplify some of the script:

LUA

function is_even(x)
    return ((x & 1) == 0)
end

Set other LEDs (present depending upon target hardware) to GND in order to not obscure the fading LED.

LUA

-- Set other LEDs to GND

set_gpio(PIN2, LOW)
set_gpio(PIN3, LOW)

The core LED fade algorithm is as follows:

LUA

for i=1,LOOP_COUNT do
    for j=5,PWM_MAX do
        if is_even(i) then
            set_pwm(PWM_PIN, j)
            msleep_f(100/j)
        else
            set_pwm(PWM_PIN, (PWM_MAX-j))
            msleep_f(100/((PWM_MAX+5)-j))
        end
    end
end

On many of the Beta release hardware boards, PIN1 is also tied to LED4. If running on a Beta release board, you will notice LED4 fade in and out (so don’t require external hardware to achieve this).

Finally, lets discard all of the variables, functions etc, that are now unused (to re-acquire the memory they utilise). Also, for good measure, force a garbage collection.

LUA

PWM_PIN = nil
LOOP_COUNT = nil

reset_all_io_type_cfg = nil
set_io_type_cfg = nil
set_pwm = nil
msleep_f = nil

collectgarbage()

That’s it!

References

API

Command Mode