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  • Author Author: shabaz
  • Date Created: Date Created
  • Views 4942 views
  • Likes 9 likes
  • Comments 14 comments
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Raspberry PIO Stepper Library: Trying it out with a Pi Pico and two Stepper Motors!

shabaz

Stepper motors are super-useful for precision movements.

I made a little stepper motor board a while back, but never got around to testing it at the time.

Jan  has created a stepper motor control library (click here to learn about it:  Raspberry PIO stepper library documentation - 1: intro, set up project and simple example )  that uses special hardware inside the Pi Pico chip, called PIO. The PIO hardware allows for precise control of inputs and outputs. 

The PIO is used to pulse an output that goes to a Toshiba chip which translates that to higher-current outputs in a sequence to drive the coils of the motor.

The video shows a quick first test of the board, using Jan's stepper motor library.

Here's another short video; showing interaction from a terminal/console connection. This will be useful when trying out new stepper motors and mechanisms, to experiment and discover what speeds and steps are needed:

 

The stepper motors/leadscrew/linear rails combo were purchased from AliExpress quite a while ago. The particular AliExpress seller no longer has more to sell, but I have seen that other AliExpress sellers have very similar-looking options.

I need to experiment a bit more, but it's great to see the board operational with the stepper motor code.

The circuit diagram is below (this is a more recent revision 1.1, compared to the revision 1.0 board which I used. The rev 1.1 board is directly compatible with Jan's stepper motor library, whereas the older rev 1.0 board needs a few resistor changes). The PDF circuit diagram is downloadable here.

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If you wish to build the board, see the pico-dual-stepper GitHub repo for the Gerber files.

Top layer:

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3D render:

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The underside doesn't have any components:

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The PDF Parts List is available here.

 

  • in reply to dougw

    Purely chance! I had dabbled with timer-driven code, but didn't do much. It was easy to take Jan's library (doesn't even need manual downloading/installing; the make file (CMakeLists.txt) contains a special fetch command that will automatically grab it and build with it) and just drop in the code to control the I/O expander which is the only board-specific part, since it sets up the Toshiba driver chips.

    It was just luck that it was easy to re-map the pins to be consecutive by re-wiring a few resistors.

  • Very cool.

    Making things move is the first step to making interesting applications.

  • in reply to BigG

    > Say, would this PIO code work on the Raspberry Pi 5? 

    The PIO code should port just fine. The C++ wrapper would possibly need redesign - in particular the interrupt part - because that's Pico specific.
    (not sure if I'd do that on a Pi though - because it may have enough resources (threads) to run stepper motors in parallel on Linux without hickups.)

  • Great demo and great teamwork, even if not planned.

    Say, would this PIO code work on the Raspberry Pi 5? 

    Would make for another interesting demo, if it's possible.

  • in reply to dougw

    Good that the pcb exists :) - I wasn't able to test 2 motors. And these linear steppers are great to check if things are in sync.

      , it probably doesn't matter, but you can make the two state machines start at exactly the same time, if you enable them via this API:  pio_set_sm_mask_enabled (PIO pio, uint32_t mask, bool enabled): Enable or disable multiple PIO state machines

    First disable them with the same call. Send the commands, then enable.

    You can then have them start at exactly the same Pico clock tick.

    I don't think it really matters, because there are several mechanical tollerances at play that are larger than the few ticks between enabling SM1 and 2 separately in C code ...