Driving a Unipolar stepper motor using ULN2803 + PIC16F887

Recently I dissembled an old Canon S200SP printer to get some motors. I found a unipolar stepper motor with 5 wires on it. But the model number is unclear as the motor is bit rusted. I tried to give a try.

First thing you have to do it check the resistance between the wires. You will find a wire which has lowest resistance with other wires. This is the centre tap. In my case,it is the red wire and in most cases this wire will be red.

Electronics-diy.com has a good article on stepper motor basics and about windings. I’m not going to tell those again and you can refer to that page.

I simply modified my general ULN2803 driver circuit to drive the stepper motor in single stepping mode (powering up single coil at a time) . I connected stepper motor to ULN2803 as loads according to the 2nd picture.

Now,It is time to do the coding,I simply edited previous MickroC code and same configuration bits were selected The bolded code is for single stepping mode

void main() {     osccon = 0x70;     ansel  = 0;     anselh  = 0;     trisa = 0;     trisb = 0;     trisc = 0;     trisd = 0;      for(;;){   portd.f4=1;     porta.f7=1;   porta.f6=0;   portc.f0=0;   portc.f1=0;   delay_ms(10);   porta.f7=0;   porta.f6=1;   portc.f0=0;   portc.f1=0;     delay_ms(10);     porta.f7=0;   porta.f6=0;   portc.f0=1;   portc.f1=0;   delay_ms(10);     porta.f7=0;   porta.f6=0;   portc.f0=0;   portc.f1=1;   portd.f4=0;   delay_ms(10);       delay_ms(2000);   }     }

Let’s check the working circuit

If everything is correctly done,Your motor will be in continuous run I’m going to get some angle measurements and to add a LCD to this project. Stay tuned and follow me on twitter @incrediblediy