DRIVING STEP-MOTORS
by Axel Kilian

Hong Ma's help was crucial in helping to make it work (thank you)- I used assembly code for programming the code through uing MPLAB by www.microchip.com

http://www.microchip.com/1010/pline/tools/software/index.htm

using a serial cable and the programming pic-chip dock The circuit for driving the the steppermotors from the output ports of the PIC I found on this site

http://eio.com/jasstep.htm

a pretty good introduction and tutorial about steppermotors and how to drive it - the diagram is Figure 2.1 - I could take it pretty much literaly as supplied using hex inverters MM74HC4049 and 10 K resistors and the sN3904 powertransitors.

Through measuring the resistance between the cable pairs in the stppermotor (it has 6 cables) we were able to single out the 2 centertab cables (see figure 3.1) the resistance of the center tab to any of the other cables is half of that of the cables going through the entire spool of the unipolar steppermotor.

Next step was writing the assembly code for the PIC we used a template and some code sniplet from another chip application and put it together - see file f876tem2.asm f876tem2.asm

One problem I had with PIC was I had forgotten to tie MCLR to high (5V) also the PIC needs to be supplied with a 20MHZ oscillator crystal (with capacitors embedded - otherwise you have to add them one between both outerpin and center pin) oscillator is directly conneted to CLKIN and CLKout pins 9 and 10 of PIC. - power PIC at pin 20 VDD and ground it at pin 19 VSS and PIN 8 VSS

The stepper motor driver cables go into the emitter of the four powertransitors - sequence has to be tested by giving them pulses while connecting the centertabs to 5V and see which direction it turns.

Then connect center tabs of steppermotor to external powersource that corresponds to Voltage specs of the motor. Now driving the motor through the assembly pattern should turn the motor the desired way.

assembly code - crucial is setting portB as output pin
1-4 in this case through the Hex number E1 - or 00011110

then loop through and set one of the pins high while others low to drive the steppermotor with the correct pattern - the DLOOP sets the time between each step.