4/11/2024 0 Comments Arduino mega ocr pinoutSpecifically, using a timer frees the arduino from having to toggle pins during every single half step. Thanks for the thoughts! In my original planning for this application, I had feared that by directly toggling the pins from within the ISR, I would be making the ISRs too long and possibly too frequent. But you should consider creating the pulses in the ISR and control several steppers with one timer. Maybe there are some restrictions that don't allow this lib in your sketch. Again, please see my "simple example" above which demonstrates this ability. If I vary this OCR value at some points throughout the timer operation (using the ISR on the output compare match in my CL42T test code), then I vary the frequency of the output on the OCnx pin. (assume step pin starts LOW, timer count is initially set to zero, and OCR set to some value greater than zero)Īs you can see, the OCR value represents the "half period" of the period between step pulses from the output compare unit. Each time the counter matches "OCR", the pin is toggled: Think of it this way: I'm counting to some value, "OCR", then the timer value resets to zero and continues counting. If I can define the period, I can define the frequency. In addition to the counter resolution, the TOP value defines the period time for waveforms generated by the Waveform Generator. Here's a nice quote from page 142 of the datasheet (in the Output Compare Units section): I think you may be missing the detail that I'm placing the timer in CTC mode (specifically, mode 4). There is something that you seem not to understand yet. StepsTaken = 0 // initialize steps taken to zero OCR_array = (OCRo*(sqrt((i*speedIncreaseStepInterval)+1)-sqrt((i*speedIncreaseStepInterval)))) OCR_array = OCRo // set first OCR value in OCR arrayįor (int i=1 i<(sizeof(OCR_array)/2) i++) SpeedIncreaseStepInterval = accelSteps / ((sizeof(OCR_array)/2)-1) // figure out speed update interval based on OCR array size MaxAccelSteps = ((Steps*Decel)/(Accel+Decel)) // steps before deceleration phaseĭecelSteps = (maxSpeedSteps*(Accel/Decel)) MaxSpeedSteps = ((MaxSpeed*MaxSpeed)/(2*mmPerStep*Accel)) // steps to reach maxSpeed OCRo = ((CntFreq/2)*sqrt((2*mmPerStep)/Accel)) // calculate first OCR value based on acceleration OCRmin = ((mmPerStep*(CntFreq/2))/MaxSpeed) // calculate minimum OCR value based on maxSpeed If (stepsTaken % speedIncreaseStepInterval = 0) If (stepsTaken = (numSteps - decelSteps)) #define StartTimer3 TCCR3B |= (1= numSteps) Here is an example sketch that can be used to reproduce the "ramp frequency" of the stepper motor, by varying the OCR value from within the output compare ISR (again using timer 3 in this sketch): #include "math.h"
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