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FadeLED

The FadeLED library provides the ability to turn LEDs on and off with fade-in/fade-out effects, using PWM-capable GPIO pins on the Arduino-class board. The library contains four classes.

  • The FadeLED class is subclassed from StateMachine (https://github.com/twrackers/StateMachine-library). This class handles the state and timing logic which is common to the other three classes.
  • The FadeLED_Lin class is subclassed from FadeLED, and provides the additional logic to perform a linear fade from fully off to fully on and back. The times required for the turning-on and turning-off fades are set independently when calling the constructor. When used to drive an LED, the linear fade mimics a light which is intentionally turned on and off slowly, such as the large red beacons which illuminate radio towers at night. The slow fade on and off of these beacons, usually large incandescent lamps, reduces the thermal shock on their filaments, extending their lives.
  • The FadeLED_Exp class is also subclassed from FadeLED, and produces an exponential fade effect. This mimics a large incandescent bulb which is not faded in a controlled manner, but takes a finite time to go from off to on as the filament heats up. Similarly, this type of bulb also takes some time to go fully dark when power is removed. Because these are thermal effects, they naturally follow exponential curves both turning on and off.
  • The FadeLED_Func class is also subclassed from FadeLED. It defines no specific fade effect, but allows the calling code to create an arbitrary one. This is done by calling the get() method after updating the object, which will return a value of type double between 0.0 and 1.0, where 0.0 is fully off and 1.0 is fully on. A new value in this range can then be computed and passed back to the object with the set() method, to be converted to the appropriate integer value and written to the PWM analog output. See the Lighthouse example code to see how this can be done.

Active-low support

LEDs connected to Arduino PWM pins are usually connected with the anode (+) to the PWM pin and the cathode (-) to ground. The FadeLED constructor for using internal PWM pins has an invert parameter which defaults to false. Setting it to true allow an LED to be connected with anode to Vcc and cathode to PWM, in a pull-down manner.

Examples

The FadeLED library contains several sketches in the examples directory.

  • SimpleLightbulb simulates a single incandescent bulb with visible turn-on and turn-off times, using the FadeLED_Exp subclass.
  • LightbulbSim simulates three incandescent bulbs with different turn-on and turn-off times.
  • BeaconSim simulates three slow-fade lights like those used on transmitter and cell towers. This uses the FadeLED_Lin subclass.
  • Faders shows the difference in appearance between a linear and an exponential fade curve.
  • Lighthouse shows how the FadeLED_Func can create a custom fade curve.

Examples of linear and exponential fade curves can be seen here.

Dependencies

FadeLED requires the StateMachine class. FadeLED_Lin, FadeLED_Exp, and FadeLED_Func only require FadeLED.

Installation

Instructions for installing the FadeLED library can be found in file INSTALL.md in this repository at https://github.com/twrackers/FadeLED-library/blob/main/INSTALL.md.