stepper-motor-controller

Package for controlling a stepper motor via remote procedure calls (RPC) utilizing base-node-rpc.

Overview

This package contains:

• Firmware compatible with Arduino Uno.
• Installable Python package for interfacing with Arduino firmware through serial port or i2c (through a serial-to-i2c proxy).

Install

The Python package can be installed through pip using the following command:

pip install stepper-motor-controller

Upload firmware

To upload the pre-compiled firmware included in the Python package, run the following command:

python -m stepper_motor_controller.bin.upload uno

This will attempt to upload the firmware by automatically discovering the serial port. On systems with multiple serial ports, use the -p command line argument to specify the serial port to use. For example:

python -m stepper_motor_controller.bin.upload -p COM3 uno

Hardware

This package is designed to work with the Pololu A4988 Stepper Motor Driver Carrier and an Arduino Uno compatible microcontroller development board. Connect the pins on the Pololu driver board as follows:

Instructions for figuring out the wiring of the stepper motor can be found here.

**Note: you must set the current limiting screw on the driver board following the online instructions (this limit is dependent on the capabilities of the motor you are using). Failure to complete this step may cause permanent damage to the motor driver!

Usage

After uploading the firmware to the board, the stepper_motor_controller.Proxy class can be used to interact with the Arduino device.

See the session log below for example usage.

Example interactive session

>>> from stepper_motor_controller import SerialProxy

Initialize a serial proxy (the computer will scan all available serial ports until it finds a match).

>>> proxy = SerialProxy()

Query the number of bytes free in device RAM.

>>> proxy.ram_free()
325 

Query descriptive properties of device.

>>> proxy.properties
base_node_software_version
package_name                                           stepper-motor-controller
display_name                                           stepper-motor-controller
manufacturer                                                      Sci-Bots Inc.
url                           http://github.com/sci-bots/stepper-motor-contr...
software_version                                                      0.1.post3
hardware_version                                                            0.1
dtype: object

Use Arduino API methods interactively.

>>> # Set pin 13 as output
>>> proxy.pin_mode(13, 1)
>>> # Turn led on
>>> proxy.digital_write(13, 1)
>>> # Turn led off
>>> proxy.digital_write(13, 0)

Configuration and state

The device stores a configuration and a state. The configuration is serialized and stored in EEPROM, allowing settings to persist across device resets. The state is stored in device memory and is reinitialized each time the device starts up.

Print configuration values.

>>> proxy.config
steps_per_revolution    200
i2c_address              10
microstep_setting         1
dtype: object

Update the configuration settings.

>>> result_code = proxy.update_config(i2c_address=32)

Other methods

Below is a list of the attributes of the stepper_motor_controller.Proxy Python class. Note that many of the Arduino API functions (e.g., pin_mode, digital_write, etc.) are exposed through the RPC API.

>>> proxy.
analog_read                     max_i2c_payload_size
analog_write                    max_serial_payload_size
array_length                    microseconds
base_node_software_version      milliseconds
begin                           move
delay_ms                        on_config_i2c_address_changed
delay_us                        on_config_microstep_setting_changed
digital_read                    package_name
digital_write                   pin_mode
display_name                    ram_free
echo_array                      read_eeprom_block
eeprom_e2end                    reset
get_buffer                      reset_config
hardware_version                reset_state
help                            save_config
i2c_address                     serialize_config
i2c_available                   serialize_state
i2c_buffer_size                 set_clock
i2c_disable_broadcast           set_i2c_address
i2c_enable_broadcast            software_version
i2c_packet_reset                stop
i2c_read                        str_echo
i2c_read_byte                   terminate
i2c_request                     update_config
i2c_request_from                update_eeprom_block
i2c_scan                        update_state
i2c_write                       url

Firmware development

The Arduino firmware/sketch is located in the stepper_motor_controller/Arduino/stepper_motor_controller directory. The key functionality is defined in the stepper_motor_controller::Node class in the file Node.h.

Running the following command will build the firmware using SCons for Arduino Uno, and will package the resulting firmware in a Python package, ready for distribution.

paver bdist_wheel 

Adding new remote procedure call (RPC) methods

New methods may be added to the RPC API by adding new methods to the stepper_motor_controller::Node class in the file Node.h.

Authors

This work is released under an MIT license.

Christian Fobel christian@fobel.net
Ryan Fobel ryan@fobel.net