Turning a stepper motor with Elixir

README.md

Turny is an Elixir port of the Adafruit Python Library for DC + Stepper Motor HAT, which is a Python library for interfacing with the Adafruit Motor HAT for Raspberry Pi to control DC motors with speed control and Stepper motors with single, double, interleave and microstepping, designed specifically to work with the Adafruit Motor Hat.

To reconstruct the Elixir project, execute mix new turny and then copy mix.exs and lib/turny.ex into place.

Run it with:

$ mix run -e Turny.start
(CTRL-c twice to stop it)
$ mix run -e Turny.swrst

Note: Be sure to do the software reset or you will leave one or more of the coils energized and the motor will get very hot.

In program code, use something like the stop function to set all the channels you're using to zero, or examine the Python code for "Release"-ing a motor to see if it does something different. I haven't gotten there yet.

The current code is doing double coil stepping where two coils are energized at once. This is much stronger than single coil stepping, but uses more power. Other options are interleaved, which alternates between single and double, and micro-stepping.

LICENSE.md

Turny is an Elixir port of the Adafruit Python Library for DC + Stepper Motor HAT, which is a Python library for interfacing with the Adafruit Motor HAT for Raspberry Pi to control DC motors with speed control and Stepper motors with single, double, interleave and microstepping, designed specifically to work with the Adafruit Motor Hat

----> https://www.adafruit.com/product/2348

Adafruit invests time and resources providing this open source code, please support Adafruit and open-source hardware by purchasing products from Adafruit!

Written by Limor Fried for Adafruit Industries. MIT license, all text above must be included in any redistribution

The MIT License (MIT) Copyright © 2016 Wendy Smoak wsmoak@gmail.com

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

mix.exs

defmodule Turny.Mixfile do
  use Mix.Project

  def project do
    [app: :turny,
     version: "0.0.1",
     elixir: "~> 1.2-rc",
     build_embedded: Mix.env == :prod,
     start_permanent: Mix.env == :prod,
     deps: deps]
  end

  # Configuration for the OTP application
  #
  # Type "mix help compile.app" for more information
  def application do
    [applications: [:logger]]
  end

  # Dependencies can be Hex packages:
  #
  #   {:mydep, "~> 0.3.0"}
  #
  # Or git/path repositories:
  #
  #   {:mydep, git: "https://github.com/elixir-lang/mydep.git", tag: "0.1.0"}
  #
  # Type "mix help deps" for more examples and options
  defp deps do
    [
      {:elixir_ale, "~> 0.4.1"}, 
    ]
  end
end

turny.ex

defmodule Turny do
  require Logger
  use Bitwise 
  
  @mode1      0x00 # bit 4 is SLEEP 000X0000
  @mode2      0x01
  @prescale   0xFE

  @all_on_l   0xFA
  @all_on_h   0xFB
  @all_off_l  0xFC
  @all_off_h  0xFD

  @led0_on_l  0x06
  @led0_on_h  0x07
  @led0_off_l 0x08
  @led0_off_h 0x09
  
  @allcall 0x01
  @outdrv 0x04
  @swrst 0x06

  # These seem to be some of the 16 channels on the PCA9685
  # I think the diagrams in the tutorial show how the PCA9685 is connected to the TB6612's on the board
  # https://learn.adafruit.com/adafruit-dc-and-stepper-motor-hat-for-raspberry-pi?view=all
  @pwma  8
  @ain2  9
  @ain1  10
  @pwmb  13
  @bin2  12
  @bin1  11

  def start do
    Logger.debug "Starting..."
     {:ok,pid}= I2c.start_link("i2c-1", 0x60)
    init(pid)
    prescale(pid, 1600) # set pwm to 1600 Hz 
    set_pwm_ab(pid)
    turn(pid)
  end

  # PCA9685 Software Reset (Section 7.6 on pg 28)
  def swrst do
    Logger.debug "PCA9685 Software Reset..."
    {:ok,pid}=I2c.start_link("i2c-1", 0x00)
    :timer.sleep 10
    I2c.write(pid,<<@swrst>>)
  end

  def init(pid) do
    Logger.debug "Initializing..."
    
    set_all_pwm(pid,0,0) 

    I2c.write(pid, <<@mode2, @outdrv>>) # external driver, see docs
    I2c.write(pid, <<@mode1, @allcall>>) # program all PCA9685's at once
    :timer.sleep 5 
  end

  def prescale(pid,freq) do
    Logger.debug "Setting prescale to #{freq} Hz" 

    # pg 14 and solve for prescale or example on pg 25
    prescaleval = trunc(Float.round( 25000000.0 / 4096.0 / freq ) - 1 )
    Logger.debug "prescale value is #{prescaleval}"

    oldmode = I2c.write_read(pid, <<@mode1>>, 1)
    :timer.sleep 5
    I2c.write(pid, <<@mode1, 0x11>>) # set bit 4 (sleep) to allow setting prescale
    I2c.write(pid, <<@prescale, prescaleval>> )
    I2c.write(pid, <<@mode1, 0x01>> ) #un-set sleep bit
    :timer.sleep 5 # pg 14 it takes 500 us for the oscillator to be ready

    I2c.write(pid, <<@mode1>> <> oldmode ) # put back old mode

  end

  def step_one(pid) do
    set_pin(pid,@ain2,1)
    set_pin(pid,@bin1,1)
    set_pin(pid,@ain1,0)
    set_pin(pid,@bin2,0)
  end
 
  def step_two(pid) do
    set_pin(pid,@ain2,0)
    set_pin(pid,@bin1,1)
    set_pin(pid,@ain1,1)
    set_pin(pid,@bin2,0)
  end

  def step_three(pid) do
    set_pin(pid,@ain2,0)
    set_pin(pid,@bin1,0)
    set_pin(pid,@ain1,1)
    set_pin(pid,@bin2,1)
  end

  def step_four(pid) do
    set_pin(pid,@ain2,1)
    set_pin(pid,@bin1,0)
    set_pin(pid,@ain1,0)
    set_pin(pid,@bin2,1)
  end

  def stop(pid) do
    set_pin(pid,@ain2,0)
    set_pin(pid,@bin1,0)
    set_pin(pid,@ain1,0)
    set_pin(pid,@bin2,0)
  end

  def turn(pid) do
    Logger.debug "turning..."
    step_one(pid)
    :timer.sleep 10
    step_two(pid)
    :timer.sleep 10
    step_three(pid)
    :timer.sleep 10
    step_four(pid)
    :timer.sleep 10
    turn(pid) 
  end

  def set_pin(pid,channel,0) do
    set_pwm(pid,channel,0,0x1000)
  end

  def set_pin(pid,channel,1) do
    set_pwm(pid,channel,0x1000,0)
  end

  # These don't need to change unless you are micro-stepping
  def set_pwm_ab(pid) do
    set_pwm(pid, @pwma, 0, 0x0FF0)
    set_pwm(pid, @pwmb, 0, 0x0FF0)  
  end

  # The registers for each of the 16 channels are sequential
  # so the address can be calculated as an offset from the first one
  def set_pwm(pid, channel, on, off) do
    I2c.write(pid, <<@led0_on_l+4*channel, on &&& 0xFF>>)
    I2c.write(pid, <<@led0_on_h+4*channel, on >>> 8>>)
    I2c.write(pid, <<@led0_off_l+4*channel, off &&& 0xFF>>) 
    I2c.write(pid, <<@led0_off_h+4*channel, off >>> 8>>)
  end

  # The PCA9685 has special registers for setting ALL channels
  # (or 1/3 of them) to the same value. 
  def set_all_pwm(pid, on, off) do
    I2c.write(pid, <<@all_on_l, on &&& 0xFF>>)
    I2c.write(pid, <<@all_on_h, on >>> 8>>)
    I2c.write(pid, <<@all_off_l, off &&& 0xFF>>)
    I2c.write(pid, <<@all_off_h, off >>> 8>>)
  end
end