onionPwm

Description:

import onionPwm

Since Omega firmware build 195, the Omega2 family supports up to 4 oboard PWM channels through the linux /sys interface. However, unlike the PWM Expansion Board, there was no Python 3 compatible library for interfacing with these channels. The onionPwm library does fix this problem by providing easy access to the PWM channels.

Features:

• Change the frequency and duty cycle of each PWM channel (See Usage)

• Provides methods to enable/disable each PWM channel (See Usage)

• Context manager support

• Python 3 compatible

Usage:

Initialize a PWM channel:

channel = onionPwm.OnionPwm( channel , chip=0 , force=False )

• If the PWM channel specified with channel does not exist, you will get OSError: [Errno 19] No such device

• If the PWM chip specified with chip does not exist, you will get FileNotFoundError

• force = True ignores if the corresponding PWM chnnel is busy. Useful if the previous user forgot to call release(), but may lead to errors if the channel is still in use.

• When not using a context manager, call release() at the end to release the PWM channel

Change the frequency of a PWM channel:

channel.set_frequency( frequency in Hz )

• If the choosen frequency is not supported by the PWM chip, you will get Permission Error: [Errno 1] Operation not permitted

channel.get_frequency() --> frequency in Hz

The result may slightly vary from the value set with setFrequency() due to rounding

Change the period of a PWM channel:

channel.set_period( period in ns )

• Similar to set_frequency(), but instead accepts values in ns

• If period is zero or negative, you will get OSError: [Errno 22] Invalid argument

• When period is smaller than the current channel duty cycle, you will get OSError: [Errno 22] Invalid argument

Please use setFrequency() instead of setPeriod() for normal operation

channel.get_period() --> Period in ns

• Similar to get_frequency(), but instead returns values in ns

Change the duty cycle of a PWM channel:

channel.set_duty_cycle( dutyCycle in percent )

• When no frequency is set, set_cycle and get_duty_cycle() will always set/report channel.get_duty_cycle() --> duty cycle in percent

channel.set_cycle( cycle in ns )

• Similar to set_duty_cycle(), but instead accepts values in ns

• When cycle is negative, you will get OSError: [Errno 22] Invalid argument

• When cycle is greater than the current channel period, you will get OSError: [Errno 22] Invalid argument

Please use setDutyCycle() instead of setCycle() for normal operation

channel.get_cycle() --> duty cycle in ns

• Similar to get_duty_cycle(), but instead returns values in ns

The result may slightly vary from the value set with setDutyCycle() due to rounding

Enable/disable a PWM channel:

channel.enable()

channel.disable()

• enable / disable the channel

is_enabled() --> True or False

Hint:

• onionPwm.toNsec( frequency in Hz ) converts a frequency in Hz into the corresponding period in ns

• onionPwm.toHz( period in ns ) converts a period in ns into the corresponding frequency in Hz

Supports:

• Python 3.5+

License:

This project is licensed under the LGPL License - see the LICENSE file for details

Authors:

• Armin W. Wer-Wolf

Acknowledgments:

• Read the Article about the PWM on how to enabling the corresponding PWM pins