Control a Stepper Motor With PWM

Ever wanted to control several stepper motors precisely with just one microcontroller? Use PWM! Instead of bit-banging and writing your own delay functions to create square waves, you can use the builtin timers and pin-change interrupts available on most hobbyist microcontrollers.

In this case we'll use a Teensy LC, a Pololu DRV8825 driver and a NEMA 17 stepper motor.

Wiring and Connections

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First solder headers to your DRV8825 board and Teensy, then put them on a breadboard. (It's actually easiest to solder these headers while the boards are already on a breadboard, but work in whatever order you'd like!)

We will connect the stepper driver much like the diagram from Pololu's product page (also included in the image below).

VMOT and GND will have a 100uF capacitor between them and be connected to a 12V benchtop supply capable of supplying at least 2A.
The ~RESET and ~SLEEP pins will be held high by connecting them to the teensy's 5V rail.
The stepper itself will connect to A1, A2, B1 and B2.
Set the stepper into 1/16 step mode by pulling M2 high and allowing M0 and M1 to float.
The driver's GND pin will connect to the teensy GND.
The teensy's pin 2 will connect to the driver's DIR pin.
And the teensy's pin 3 will connect to the driver's STEP pin.

The teensy will have one additional connection: pin 9 will be tied to pin 3. This will allow the teensy to count pulses via a pin-change interrupt.

Also make sure to set the DRV8825's current limiting resistor to an appropriate value, as described on their product page.

Coding!

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I used teensyduino to write a little arduino-like sketch to control the stepper motor. Follow the teensyduino setup steps here to get your coding environment setup correctly.

The code will allow us to send a command from the terminal to control the stepper's position. The full sketch is posted here. Each image below will breakdown a section of the code. And there's also a quick demo of the controller in action!

What's Next..

Some things you could try next:

add limit switches to control the max and min extent of the stepper's travel
experiment with acceleration to get the stepper quickly up to speed
try different microstepping values -- the DRV8825 supports full step to 1/32 microsteps

If you try any of these, post your results in a comment below!