"""Motor control related classes.
Examples
--------
>>> from pslab.external.motor import Servo
>>> servo = Servo("SQ1")
>>> servo.angle = 30 # Turn motor to 30 degrees position.
"""
from typing import Union
from pslab.instrument.waveform_generator import PWMGenerator
MICROSECONDS = 1e6
[docs]class Servo:
"""Control servo motors on SQ1-4.
Parameters
----------
pin : {"SQ1", "SQ2", "SQ3", "SQ4"}
Name of the digital output on which to generate the control signal.
pwm_generator : :class:`PWMGenerator`, optional
PWMGenerator instance with which to generate the control signal.
Created automatically if not specified. When contolling multiple
servos, they should all use the same PWMGenerator instance.
min_angle_pulse : int, optional
Pulse length in microseconds corresponding to the minimum (0 degree)
angle of the servo. The default value is 500.
max_angle_pulse : int, optional
Pulse length in microseconds corresponding to the maximum (180 degree)
angle of the servo. The default value is 2500.
angle_range : int
Range of the servo in degrees. The default value is 180.
frequency : float, optional
Frequency of the control signal in Hz. The default value is 50.
"""
def __init__(
self,
pin: str,
pwm_generator: PWMGenerator = None,
min_angle_pulse: int = 500,
max_angle_pulse: int = 2500,
angle_range: int = 180,
frequency: float = 50,
):
self._pwm = PWMGenerator() if pwm_generator is None else pwm_generator
self._pin = pin
self._angle = None
self._min_angle_pulse = min_angle_pulse
self._max_angle_pulse = max_angle_pulse
self._angle_range = angle_range
self._frequency = frequency
@property
def angle(self) -> Union[int, None]:
""":obj:`int` or :obj:`None`: Angle of the servo in degrees."""
return self._angle
@angle.setter
def angle(self, value: int):
duty_cycle = self._get_duty_cycle(value)
self._pwm.generate(self._pin, self._frequency, duty_cycle)
self._angle = value
def _get_duty_cycle(self, angle):
angle /= self._angle_range # Normalize
angle *= self._max_angle_pulse - self._min_angle_pulse # Scale
angle += self._min_angle_pulse # Offset
return angle / (self._frequency ** -1 * MICROSECONDS)