Blynk app
DRV8825 stepper driver
Blynk can send and receive data to internet devices using it’s free app. You can also host your own Blynk server for security.
To send an adjustable frequency from the Arduino to the DRV8825 I used the tone command, a square wave is perfect.
The tone command:
tone(pin, frequency)
tone(pin, frequency, duration)
calling it with 2 parameters the frequency is output once, I want the frequency to output continually so there needs to be a duration, but the longer the duration the less responsive it is. Measuring the speed of the loop can be done with a set/clear with a state = !state, while including Blynk.