Control a stepper motor with an arduino
Here is the way I control my stepper motor (NEMA 14) with an arduino and a pololu A4988.
First of all the electronic schema :
I found lot of code regarding the control of the motor but nothing accurate enough for astronomy.
To be more accurate as possible, I use the timer of the arduino Leonardo which has a microsecond resolution plus an algorithm to compensate the lack of accuracy.
If you directly use the hardware timer, you will have a drift of 1 arc.sec per minute which is unacceptable.
With the algorithm, the accuracy go up to 99.99987% which represent an error of 0.0076 arc.second per minute ! Great !
First of all, you have to get the “TimerOne” library. It's directly accessible from the arduino IDE.
Then, this piece of magic will do the trick (it's not yet finished for the fast speed part but the sideral speed is ok):
#include // 20 bits after the floating point, has to be ajusted regarding the speed // Eg: For a freq of 10kHz, 24 is a good value, // For a freq of 1.7 kHz, 20 seams accurate #define motEnable 6 #define motStep 5 #define motDir 4 #define MS1 7 #define MS2 8 #define MS3 9 #define INITFREQ (90) #define STEP_SHIFT (20) const int freq = 10369; void setup(void) { Timer1.initialize(INITFREQ); // Call interupts each 90µs // 1 full tr in 86164 seconds witch is demultiplied by 6^7 // it requires the motor to do 3.248874 tr/s // 3.24887423982 tr/s x 200 steps x 16 microsteps = 10369.3975674 impulses/s // Impules @ 10.369 kHz, so wait 90µs // 1 full tr in 86164 seconds witch is demultiplied by 6^6 // it requires the motor to do 0.54147903997 tr/s // Impules @ 1732.7329279 Hz, so wait 577.1236550497256 µs pinMode(motEnable,OUTPUT); // Enable pinMode(motStep,OUTPUT); // Step pinMode(motDir,OUTPUT); // Dir digitalWrite(motEnable,LOW); // Set Enable low digitalWrite(motDir,LOW); // Set Dir high pinMode(MS1,OUTPUT); // MS1 pinMode(MS2,OUTPUT); // MS2 pinMode(MS3,OUTPUT); // MS3 // Set microstep mode setMicroStep(); Timer1.attachInterrupt(sideralSpeed); Serial.begin(9600); Serial.println("Motor stepper test"); Serial.println("Starting now !"); } void setMicroStep(void) { // Set microstep mode digitalWrite(MS1,HIGH); digitalWrite(MS2,HIGH); digitalWrite(MS3,HIGH); } void setFullStep(void) { // Set fullstep mode digitalWrite(MS1,LOW); digitalWrite(MS2,LOW); digitalWrite(MS3,LOW); } // Keep a track of the accumulated delay uint32_t StepCons=(577.1236550497257)*pow(2,STEP_SHIFT); uint32_t lastStepErr = 0; uint32_t StepCurr = StepCons; void sideralSpeed(void) { digitalWrite(motStep,HIGH); // Impulse start digitalWrite(motStep,LOW); // Impulse stop. StepCurr = StepCons + lastStepErr; Timer1.setPeriod(StepCurr>>STEP_SHIFT); //Serial.println(StepCurr>>STEP_SHIFT); lastStepErr = StepCurr & (((uint32_t)~0)>>(32 - STEP_SHIFT) ); // On prend juste le poid faible } // Begin @ 600tr/min int StepFast = 500; //0 = Clockwise , 1 = Anti-clockwise void fastSpeed(void) { digitalWrite(motStep,HIGH); // Impulse start digitalWrite(motStep,LOW); // Impulse stop. // Speed = number_of_step / time_between_steps so function like 1/x // to increase speed linearly: multiply by (constant x time_between_steps²) // Linear acceleration to 2340 tr/min if (StepFast > 129) { //10.000.000 give a nominal speed in 0.13s StepFast -= 1/10000000*pow(StepFast,2); Timer1.setPeriod(StepFast); } } void loop(void) { }
If you want to follow the code, go here : https://github.com/DrGkill/Astro-Mount-Control
