How to Drive a Stepper Motor

Please post a sketch by scanning it in and attaching it to a posting using the green camera button.

If you have BK & WT to +ve of motor supply, then a possible sequence to step would be

RD on
GN on
RD/WT on
GN/WT on

That would give full step, half power (only 1 coil energized at a time).

For two coils energized (full power), use

RD & GN/WT on
RD & GN on
RD/WT & GN on
RD/WT & GN/WT on

You may have got your coil sequence wrong. Try and find the correct sequence and reconnect to your circuit. To get you started, the white wire will have a low resistance between it and two other wires only. If the resistance is equal, the white is definitely the common and the other two wires can be driven by the 0x01 and 0x04 lines in your program. Do the same with the black wire and drive the other two wires with the 0x02 and 0x08 lines. If the motor goes the wrong way, just reverse the 0x02 and 0x08 lines.

thanks for ur comment ..but i need more help from u...i hv checked all the combinations keeping black &white as common...and given the half step sequence and full step sequence..but the motor responds by giving a step cw& then ccw and repeats...am using uln 2803a instead of uln2003a...it is identified that red,black&red strip on white forms 1 coil ,and green,white&green strip on white forms the 2nd....any other alternatives test on....please help me....

The sequences I gave in #2 for that colour coding of the coil leads are correct. Have you checked the outputs with a meter or 'scope when driving one (attempted) step at a time?

The symptom you're describing usually means one coil is not connected (open circuit) (given that the energization sequence is correct).

What is the resistance between red and black, red and red/white, black and red/white pairs of wires? Do a similar resistance check for the other three wires and reply back with six results.

red&black-33.4ohm

>rd&rd/wt-66.8

>black&rd/wt-33.6

>green&white-34.2

>grn&grn/wt-68.8

>white&grn/wt-34.8

OK. This confirms the wiring. If you have connected the coils and are driving them as JohnDG says in post #2, ie. Red = 0x01, Green = 0x02, Red/Wt = 0x04 and Green/Wt = 0x08 with Blk and Wt connected to +V, it should work.

Try slowing down the pulse rate and see if that works.

Alternatively, you may have blown up the ULN2803. What is the rating of your motor.

Do you have the common of the freewheeling diodes on the ULN2803A (pin 10) connected to the motor supply? Not using them (or some other protection) could damage the outputs.

BTW, what is the motor supply voltage?

yes...common wires and pin 10 r connected to the supply 12v...

You could also replace the stepper motor with 4 bulbs and slow the PIC clock right down to check your driving sequence. Alternatively, put a delay loop in your code and check the outputs with a meter.

try to check this site

www.luberth.com

will find what u want an much more

There are so many nice chips to drive Unipolar motors to about 3 amps max, (that must cover what you are doing with that particular driver chip!) that only need a step/clock and a direction signal (and even have micro stepping if needed). Thats only two signals, easy peasy!!

Don't try and re-invent the wheel!!!

If you let us know how many amps at what voltage your stepper motor needs, just come back and we will help you with some chip type numbers to go for.......

Hi raf23

See page 14 on this picaxe helpfile for info on programming your stepper. http://www.rev-ed.co.uk/docs/picaxe_manual3.pdf

Good luck.