I built myself a 10"x8"x3" cnc for milling pcb boards and other things and possibly in the future 3d printing. Plan is to use GRBL on an atmega328p board that I designed. Anyways even though I plan to use GRBL I want to learn and understand what is happening behind the scenes and in the end learn c and programming avrs. And maybe one day write my own code to control the cnc.
I wrote the following code just as a mechanical and electrical test of all 3 axis.
This is the first time I've worked with timers (I did do a simple blink sketch using timer CTC and had the LED on pin 13 blinking every 1 second), direct port manipulation and pointers.
/*Command all 3 axis, 1 at a time, to move until it hits its undertravel limit switch, then change direction and
move until it hits its overtravel limit switch, and then record the amount of pulses it took to go limit to limit,
divide that value in half and go to that position then stop.*/
// avr-libc library includes
#include <avr/io.h>
#include <avr/interrupt.h>
#define RUN_ENABLE 0x80 //Axis "ENABLE" Control Bit, PIN 8
int X_DIR = 0x04; //X axis "DIRECTION" Control Bit, PIN 2
int X_STEP = 0x08; //X Axis "STEP" Control Bit, PIN 3
int Y_DIR = 0x10; //X axis "DIRECTION" Control Bit, PIN 2
int Y_STEP = 0x20; //X Axis "STEP" Control Bit, PIN 3
int Z_DIR = 0x40; //X axis "DIRECTION" Control Bit, PIN 2
int Z_STEP = 0x80; //X Axis "STEP" Control Bit, PIN 3
int X_UNDERTRAVELPROX = PINC5; //X Axis over travel prox input, PIN A5
int X_OVERTRAVELPROX = PINC4; //X Axis under travel prox input, PIN A4
int Y_UNDERTRAVELPROX = PINC3; //Y Axis over travel prox input, PIN A3
int Y_OVERTRAVELPROX = PINC2; //Y Axis under travel prox input, PIN A2
int Z_UNDERTRAVELPROX = PINC1; //Z Axis over travel prox input, PIN A1
int Z_OVERTRAVELPROX = PINC0; //Z Axis under travel prox input, PIN A0
//pointers
int *STEP;
int *DIR;
int *UNDERTRAVELPROX;
int *OVERTRAVELPROX;
int *ACTUALPOS;
int *COMMANDPOS;
int *MAXSTEPS;
char activeaxis = 0;
int motionenable = 0;
int sequence = 0;
/*
seq 0 = idle
seq 1 = move active axis until under travel prox is made
seq 2 = move active axis until over travel prox is made then record
number of pulses from under travel to over travel prox
seq 3 = move active axis to center of travel
*/
int index = 0;
int xaxismaxsteps;
int xaxiscommandpos;
int xaxisactualpos;
int yaxismaxsteps;
int yaxiscommandpos;
int yaxisactualpos;
int zaxismaxsteps;
int zaxiscommandpos;
int zaxisactualpos;
int feedrate = 9999; //5ms pulse interval, 0.0492in/sec feedrate
void setup() {
DDRD |= 0xFC; // sets digital pins 2,3,4,5,6,7 as output, step and direction pins
DDRB |= 0x01; // sets digital pin 8 as output, stepper drivers enable pin
PORTD |= 0xD8; // sets digital pins 2,3,4,5,6,7 HIGH (internal pull-up resistor)
cli(); // disable global interrupts
// initialize Timer2
TCCR1A = 0; // set entire TCCR1A register to 0
TCCR1B = 0; // same for TCCR1B
// turn on CTC mode:
TCCR1B |= (1 << WGM12);
// Set CS11 bit for 8 prescaler:
TCCR1B |= (1 << CS11);
}
void loop() {
// set compare match register equal to feedrate
OCR1A = feedrate;
// enable global interrupts:
sei();
if ((sequence == 0) && (index < 3)) {
if (activeaxis == 0) { //first run
activeaxis = 'X';
//assign pointers
DIR = &X_DIR; //sets DIR to the memory address location of X_DIR
STEP = &X_STEP; //sets STEP to the memory address location of X_STEP
UNDERTRAVELPROX = &X_UNDERTRAVELPROX;
OVERTRAVELPROX = &X_OVERTRAVELPROX;
ACTUALPOS = &xaxisactualpos;
COMMANDPOS = &xaxiscommandpos;
MAXSTEPS = &xaxismaxsteps;
}
else if (activeaxis == 'X') {
activeaxis = 'Y';
//assign pointers
DIR = &Y_DIR;
STEP = &Y_STEP;
UNDERTRAVELPROX = &Y_UNDERTRAVELPROX;
OVERTRAVELPROX = &Y_OVERTRAVELPROX;
ACTUALPOS = &yaxisactualpos;
COMMANDPOS = &yaxiscommandpos;
MAXSTEPS = &yaxismaxsteps;
}
else if (activeaxis == 'Y') {
activeaxis = 'Z';
//assign pointers
DIR = &Z_DIR;
STEP = &Z_STEP;
UNDERTRAVELPROX = &Z_UNDERTRAVELPROX;
OVERTRAVELPROX = &Z_OVERTRAVELPROX;
ACTUALPOS = &zaxisactualpos;
COMMANDPOS = &zaxiscommandpos;
MAXSTEPS = &zaxismaxsteps;
}
else {
activeaxis = 0;
//assign pointers
DIR = NULL;
STEP = NULL;
UNDERTRAVELPROX = NULL;
OVERTRAVELPROX = NULL;
ACTUALPOS = NULL;
COMMANDPOS = NULL;
MAXSTEPS = NULL;
}
//set direction of active axis to reverse
PORTD &= ~*DIR;
//zero active axis position
*ACTUALPOS = 0; // zero actual steps
//command active axis to maximum negative position
*COMMANDPOS = -32768;
sequence = 1; //advance to the next sequence
motionenable = 1;
// enable timer 1 compare interrupt used for pulsing stepper driver output:
TIMSK1 |= (1 << OCIE1A);
}
if ((sequence == 1) && (*UNDERTRAVELPROX == 1)) { //under travel prox reached
motionenable = 0; // disable motion
*ACTUALPOS = 0; // zero actual steps
*COMMANDPOS = 32768; //command axis to maximum positive position
// change direction of X axis
PORTD |= *DIR; // set pin HIGH
sequence = 2; //advance to the next sequence
motionenable = 1; // enable motion
}
if ((sequence == 2) && (*OVERTRAVELPROX == 1)) {
motionenable = 0; // disable motion
*MAXSTEPS = *ACTUALPOS;
*COMMANDPOS = (*MAXSTEPS / 2);
// change direction of X axis
PORTD &= ~*DIR; // set pin LOW
sequence = 3; //advance to the next sequence
motionenable = 1; // enable motion
}
if ((sequence == 3) && (*ACTUALPOS == *COMMANDPOS)) {
motionenable = 0; // disable motion
sequence = 0; //loop back to sequence 0
index ++;
}
}
ISR (TIMER1_COMPA_vect) {
int t =0;
if (motionenable == 1) {
if((PORTD & *DIR) != ~*DIR) //If going forward, increment active axis position counter
*ACTUALPOS++;
else //If going reverse, decrement axis position counter
*ACTUALPOS--;
if (*ACTUALPOS != *COMMANDPOS) { //If we are not at our commanded position
PORTD |= *STEP; //Toggle "Step" output with each entry
while(t++ != 10);
PORTD &= ~*STEP;
}
}
}
My next code challenge will be linear interpolation, making 2 axis start and stop at the same time no matter the difference in distance that each axis has to travel.
