Pi Servo pHAT (v2) Hookup Guide

Contributors: QCPete, santaimpersonator

Python Package Overview

There are two Python packages for this product. Qwiic_PCA9685_Py is an underlying package for the operation of the PCA9685 PWM controller IC. While, PiServoHat_Py is a package, built specifically for this product, to control servos. We've written these packages to easily start controlling servos with the Pi Servo pHAT.

Installation

To install the Python packages for this product, it is recommended that users install the SparkFun Qwiic Python package, which installs all the available Python packages for our Qwiic products and includes the required I²C driver package. On systems that support PyPi installation via pip3 (use pip for Python 2) is simple, using the following commands:

For all users (note: the user must have sudo privileges):

language:bash
sudo pip3 install sparkfun-qwiic

For the current user:

language:bash
pip3 install sparkfun-qwiic

Qwiic_PCA9685_Py

You can install the sparkfun-sparkfun-qwiic-pca9685 Python package hosted by PyPi. If you prefer to manually download and install the package from the GitHub repository, you can grab them here (*Please be aware of any package dependencies. You can also check out the repository documentation page, hosted on ReadtheDocs.):

PyPi Installation

This repository is hosted on PyPi as the sparkfun-qwiic-pca9685 package. On systems that support PyPi installation via pip3 (use pip for Python 2) is simple, using the following commands:

For all users (note: the user must have sudo privileges):

language:bash
sudo pip3 install sparkfun-qwiic-pca9685

For the current user:

language:bash
pip3 install sparkfun-qwiic-pca9685

Local Installation

To install, make sure the setuptools package is installed on the system.

Direct installation at the command line (use python for Python 2):

language:bash
python3 setup.py install

To build a package for use with pip3:

language:bash
python3 setup.py sdist

A package file is built and placed in a subdirectory called dist. This package file can be installed using pip3.

language:bash
cd dist
pip3 install sparkfun_qwiic_pca9685-<version>.tar.gz

Python Package Operation

As this is an underlying package for the PCA9685 PWM controller IC, we will not go into the details of the package operation. However, users are welcome to check out the ReadtheDocs documentation.

PiServoHat_Py

You can install the sparkfun-pi-servo-hat Python package hosted by PyPi. If you prefer to manually download and install the package from the GitHub repository, you can grab them here (*Please be aware of any package dependencies. You can also check out the repository documentation page, hosted on ReadtheDocs.):

PyPi Installation

This repository is hosted on PyPi as the sparkfun-pi-servo-hat package. On systems that support PyPi installation via pip3 (use pip for Python 2) is simple, using the following commands:

For all users (note: the user must have sudo privileges):

language:bash
sudo pip3 install sparkfun-pi-servo-hat

For the current user:

language:bash
pip3 install sparkfun-pi-servo-hat

Local Installation

To install, make sure the setuptools package is installed on the system.

Direct installation at the command line:

language:bash
python setup.py install

To build a package for use with pip3:

language:bash
python setup.py sdist

A package file is built and placed in a subdirectory called dist. This package file can be installed using pip3.

language:bash
cd dist
pip3 install sparkfun_pi_servo_hat-<version>.tar.gz

Python Package Operation

Below is a description of the basic functionality of the Python package. This includes the package organization, built-in methods, and their inputs and/or outputs. For more details on how the Python package works, check out the source code and the sensor datasheet.

Dependencies

This Python package has a very few dependencies in the code, listed below:

language:python
import time             # Time access and conversion package
import math             # Basic math package
import qwiic_pca9685    # PCA9685 LED driver package

Default Variables

The default variables, in the code, for this Python package are listed below:

language:python
# Device Name:
_DEFAULT_NAME = "Pi Servo HAT"

# Fixed Address:
_AVAILABLE_I2C_ADDRESS = [0x40]

# Default Servo Frequency:
_DEFAULT_SERVO_FREQUENCY = 50   # Hz

# Special Use Addresses:
gcAddr = 0x00       # General Call address for software reset
acAddr = 0x70       # All Call address- used for modifications to
                    # multiple PCA9685 chips reguardless of thier
                    # I2C address set by hardware pins (A0 to A5).
subAddr_1 = 0x71    # 1110 001X or 0xE2 (7-bit)
subAddr_2 = 0x72    # 1110 010X or 0xE4 (7-bit)
subAddr_3 = 0x74    # 1110 100X or 0xE8 (7-bit)

Class

PiServoHat() or PiServoHat(address, debug=None)
This Python package operates as a class object, allowing new instances of that type to be made. An __init__() constructor is used that creates a connection to an I²C device over the I²C bus using the default or specified I²C address.

The Constructor

A constructor is a special kind of method used to initialize (assign values to) the data members needed by the object when it is created.

__init__(address, debug)

Functions

A function that is an attribute of the class, which defines a method for instances of that class. In simple terms, they are objects for the operations (or methods) of the class.

.restart()
Soft resets the PCA9685 chip and then clears the MODE1 register to restart the PWM functionality. The PWM frequency is also returned to the default 50 Hz setting.

.get_pwm_frequency()
Reads the PWM frequency used on the outputs.

.set_pwm_frequency(frequency)
Configures the PWM frequency used on outputs. 50 Hz is the default and recommended for most servos.

.get_servo_position(channel) or .get_servo_position(channel, swing)
Estimates the orientation of the servo arm in degrees. The estimation is based upon the timing that is configured for the PWM signal, on the specified channel.

.move_servo_position(channel, position) or .move_servo_position(channel, position, swing)
Moves servo to specified location in degrees.

.set_duty_cycle(channel, duty_cycle)
Moves servo to specified location based on duty-cycle.

Upgrading Packages

In the future, changes to the Python packages might be made. Updating the installed packages has to be done individually for each package (i.e. sub-modules and dependencies won't update automatically and must be updated manually). For the SomePackage Python package, use the following command (use pip for Python 2):

For all users (note: the user must have sudo privileges):

language:bash
sudo pip3 install --upgrade SomePackage

For the current user:

language:bash
pip3 install --upgrade SomePackage