ServoKit.PCA9685 (servo_kit v0.2.0) View Source

Sets a single PWM channel or all PWM channels by specifying when to switch on and when to switch off in a period. These values must be between 0 and 4095.

Link to this section Types

channel()

Specs

channel() :: 0..15 | :all

duty_cycles()

Specs

duty_cycles() ::
  {number(), number(), number(), number(), number(), number(), number(),
   number(), number(), number(), number(), number(), number(), number(),
   number(), number()}

Current duty cycle value of each channel. The tuple index corresponds to the channel.

frequency()

Specs

frequency() :: 24..1526

options()

Specs

options() :: [
  bus_name: ServoKit.Transport.bus_name(),
  address: ServoKit.Transport.address(),
  reference_clock_speed: pos_integer(),
  frequency: frequency()
]

t()

Specs

t() :: %ServoKit.PCA9685{
  duty_cycles: duty_cycles(),
  i2c_address: ServoKit.Transport.address(),
  i2c_ref: ServoKit.Transport.bus(),
  mode1: pos_integer(),
  prescale: pos_integer(),
  reference_clock_speed: pos_integer()
}

Link to this section Functions

frequency_from_prescale(prescale, reference_clock_speed)

Specs

frequency_from_prescale(pos_integer(), pos_integer()) :: pos_integer()

Calculates the PWM frequency in Hz based on specified prescale value and reference clock speed.

Examples

iex> PCA9685.frequency_from_prescale(255, 25_000_000)
24

iex> PCA9685.frequency_from_prescale(121, 25_000_000)
50

iex> PCA9685.frequency_from_prescale(60, 25_000_000)
102

init(opts \\ [])

Specs

init(options()) :: {:ok, t()} | {:error, any()}

Initializes the servo driver and returns the initial state.

prescale_from_frequecy(freq_hz, reference_clock_speed)

Specs

prescale_from_frequecy(24..1526, integer()) :: 3..255

Calculates the PWM frequency prescale based on the formula in data sheet 7.3.5.

Formula

prescale_value = round(osc_value / (4096 * update_rate)) - 1

Examples

iex> PCA9685.prescale_from_frequecy(24, 25_000_000)
253

iex> PCA9685.prescale_from_frequecy(50, 25_000_000)
121

iex> PCA9685.prescale_from_frequecy(100, 25_000_000)
60

iex> PCA9685.prescale_from_frequecy(1526, 25_000_000)
3

pulse_range_from_percentage(percent)

Specs

pulse_range_from_percentage(number()) :: {0, 0..4095}

Calculates 12-bit pulse range from a percentage value.

Examples

iex> PCA9685.pulse_range_from_percentage(0.0)
{0, 0}

iex> PCA9685.pulse_range_from_percentage(50.0)
{0, 2048}

iex> PCA9685.pulse_range_from_percentage(100.0)
{0, 4095}

reset(state)

Performs the software reset. See PCA9685 data sheet 7.1.4 and 7.6.

set_pwm_duty_cycle(state, percent, list)

Specs

set_pwm_duty_cycle(t(), number(), [{:ch, channel()}]) ::
  {:ok, t()} | {:error, any()}

Sets a single PWM channel or all PWM channels by specifying the duty cycle in percent.

Examples

ServoKit.PCA9685.set_pwm_duty_cycle(driver, 50.0, ch: 0)
ServoKit.PCA9685.set_pwm_duty_cycle(driver, 50.0, ch: :all)

set_pwm_frequency(state, freq_hz)

Specs

set_pwm_frequency(t(), frequency()) :: {:ok, t()} | {:error, any()}

Sets the PWM frequency to the provided value in hertz. The PWM frequency is shared by all the channels.

Examples

ServoKit.PCA9685.set_pwm_frequency(state, 50)

sleep(state)

Puts the board into the sleep mode.

wake_up(state)

Wakes the board from the sleep mode.

write_pulse_range(state, ch, arg)

Specs

write_pulse_range(t(), :all | byte(), {char(), char()}) :: t()

Sets a single PWM channel or all PWM channels by specifying when to switch on and when to switch off in a period. These values must be between 0 and 4095.