Source code for adafruit_pca9685

# SPDX-FileCopyrightText: 2016 Radomir Dopieralski for Adafruit Industries
# SPDX-FileCopyrightText: 2017 Scott Shawcroft for Adafruit Industries
# SPDX-License-Identifier: MIT


Driver for the PCA9685 PWM control IC. Its commonly used to control servos, leds and motors.

.. seealso:: The `Adafruit CircuitPython Motor library
    <>`_ can be used to control the PWM
    outputs for specific uses instead of generic duty_cycle adjustments.

* Author(s): Scott Shawcroft

Implementation Notes


* Adafruit `16-Channel 12-bit PWM/Servo Driver - I2C interface - PCA9685
  <>`_ (Product ID: 815)

**Software and Dependencies:**

* Adafruit CircuitPython firmware for the ESP8622 and M0-based boards:
* Adafruit's Bus Device library:
* Adafruit's Register library:

__version__ = "0.0.0-auto.0"
__repo__ = ""

import time

from adafruit_register.i2c_struct import UnaryStruct
from adafruit_register.i2c_struct_array import StructArray
from adafruit_bus_device import i2c_device

[docs]class PWMChannel: """A single PCA9685 channel that matches the :py:class:`~pwmio.PWMOut` API.""" def __init__(self, pca, index): self._pca = pca self._index = index @property def frequency(self): """The overall PWM frequency in Hertz (read-only). A PWMChannel's frequency cannot be set individually. All channels share a common frequency, set by PCA9685.frequency.""" return self._pca.frequency @frequency.setter def frequency(self, _): raise NotImplementedError("frequency cannot be set on individual channels") @property def duty_cycle(self): """16 bit value that dictates how much of one cycle is high (1) versus low (0). 0xffff will always be high, 0 will always be low and 0x7fff will be half high and then half low.""" pwm = self._pca.pwm_regs[self._index] if pwm[0] == 0x1000: return 0xFFFF return pwm[1] << 4 @duty_cycle.setter def duty_cycle(self, value): if not 0 <= value <= 0xFFFF: raise ValueError("Out of range") if value == 0xFFFF: self._pca.pwm_regs[self._index] = (0x1000, 0) else: # Shift our value by four because the PCA9685 is only 12 bits but our value is 16 value = (value + 1) >> 4 self._pca.pwm_regs[self._index] = (0, value)
[docs]class PCAChannels: # pylint: disable=too-few-public-methods """Lazily creates and caches channel objects as needed. Treat it like a sequence.""" def __init__(self, pca): self._pca = pca self._channels = [None] * len(self) def __len__(self): return 16 def __getitem__(self, index): if not self._channels[index]: self._channels[index] = PWMChannel(self._pca, index) return self._channels[index]
[docs]class PCA9685: """ Initialise the PCA9685 chip at ``address`` on ``i2c_bus``. The internal reference clock is 25mhz but may vary slightly with environmental conditions and manufacturing variances. Providing a more precise ``reference_clock_speed`` can improve the accuracy of the frequency and duty_cycle computations. See the ```` example for how to derive this value by measuring the resulting pulse widths. :param ~busio.I2C i2c_bus: The I2C bus which the PCA9685 is connected to. :param int address: The I2C address of the PCA9685. :param int reference_clock_speed: The frequency of the internal reference clock in Hertz. """ # Registers: mode1_reg = UnaryStruct(0x00, "<B") prescale_reg = UnaryStruct(0xFE, "<B") pwm_regs = StructArray(0x06, "<HH", 16) def __init__(self, i2c_bus, *, address=0x40, reference_clock_speed=25000000): self.i2c_device = i2c_device.I2CDevice(i2c_bus, address) self.channels = PCAChannels(self) """Sequence of 16 `PWMChannel` objects. One for each channel.""" self.reference_clock_speed = reference_clock_speed """The reference clock speed in Hz.""" self.reset()
[docs] def reset(self): """Reset the chip.""" self.mode1_reg = 0x00 # Mode1
@property def frequency(self): """The overall PWM frequency in Hertz.""" return self.reference_clock_speed / 4096 / self.prescale_reg @frequency.setter def frequency(self, freq): prescale = int(self.reference_clock_speed / 4096.0 / freq + 0.5) if prescale < 3: raise ValueError("PCA9685 cannot output at the given frequency") old_mode = self.mode1_reg # Mode 1 self.mode1_reg = (old_mode & 0x7F) | 0x10 # Mode 1, sleep self.prescale_reg = prescale # Prescale self.mode1_reg = old_mode # Mode 1 time.sleep(0.005) # Mode 1, autoincrement on, fix to stop pca9685 from accepting commands at all addresses self.mode1_reg = old_mode | 0xA0 def __enter__(self): return self def __exit__(self, exception_type, exception_value, traceback): self.deinit()
[docs] def deinit(self): """Stop using the pca9685.""" self.reset()