Arduino Stepper Motor Control of a Super 8 Projector

The Adruino Create project

Arduino CNC Shield

For some reason the wiring wasn't working for the Pi directly connected to the DRV8825. I did have a CNC Shield v3 on hand (also why I had four DRV8825s in the first place) so this is a sketch to control the stepper motor via USB serial.

Connections

The pins.h file is set up for a motor and limit switch to be connected to the X axis. The limit switch pins on the shield are wired to the same Arduino pin so +X or -X doesn't make a difference.

An LED can be connected to the Z limit pins via a MOSFET. This pin was chosen for PWM to enable adjusting the brightness. I had a N Channel STP120NF10 on hand, so I connected Gate (Pin 1) to Z Limit, Source (Pin 3) to GND, and Drain (Pin 2) to the LED's cathode (negative). The LED's anode (positive) is connected to +12V (the same driving my stepper motor). Adafruit has a good usage example.

Protocol

Text, each command is \n terminated

Stop

• S\n Stop: stops the motor and turns off the power to it.
  • MOTORS_DISABLED\n will be received when the motors stop.

Information

• I\n: Information, multiple lines logging the parameters and values will be received:
  • # current speed: 0.00\n shows the (micro)steps per second velocity the motor is told to be moving at
  • # moving speed: 3200.00\n shows the velocity that will be used for an Advance
  • # maximum speed: 10000.00\n shows what the moving speed will be capped at
  • # switch pressed: no\n shows the measured value of the limit switch (yes for on and no for off)

Advance

• AF\n: Advance Frame, will spin the stepper motor CCW until the limit switch is triggered.
  • ADVANCE_FRAME_STARTED\n will be received when the motor starts turning
  • MOTION_STOPPED\n will be received when the limit switch is triggered
  • MOTORS_DISABLED\n will be received if no Advance command is transmitted within a certain time after the limit switch is triggered.
• A\n: Advance, will spin the stepper motor CCW ignoring the limit switch
  • ADVANCE_STARTED\n will be received when the motor starts turning
• RF\n: Reverse Frame, same as Advance Frame but CW
• R\n: Reverse, same as Advance but CW
• A S 3200\n: Sets the (micro)steps per second velocity of the motor for Advancements
  • # ERR: invalid number\n is received if the value transmitted is determined to not be a number
  • no messages are received if the value is used, though the Information command can confirm the new value

Lamp

• L A\n: Lamp Activate, turn the lamp/LED
  • LAMP_ON\n is received after the PWM signal is applied
• L D\n: Lamp LAMP_DEACTIVATE, turn the lamp/LED
  • LAMP_OFF\n is received after the PWM signal is removed (that is, no pulse is applied)
• L S\n: Set the lamp brightness, also turning on the lamp if not 0
  • # ERR: invalid number\n is received if the value transmitted is determined to not be a number
  • no messages are received if the value is out of bounds
  • LAMP_ON\n or LAMP_OFF\n are received if the value is used (0 is seen as off)