Hello!
You should read about stepping motors, there is a lot of docs on the net (Your favourite search engine
will find everything). And once you understand how it works, why not writing your own algorithm?
About whole steps. As you may already know, if you send a sequence of pulses on the coils,
for example clockwise, your motor will stabilize on the coil which is active at the moment.
For example if we name the coils of your picture 0, 1, 2, 3 (o is noon, 1 is 3 o'clock, etc...) then
your motor will step accordingly. Now if you power coils 0 and 1 at the same time, the motor
will stabilize at 1:30. So if you want half stps, the power sequence is 0, 1&1, 1, 1&2, 2, 2&3, 3, 3&0,
etc... Now you can think about how to do for quarter steps...
Dora.
PS: You have sent me a request by mail.
1. I don't reply to mails because this is a forum and what I may write should be readable by anybody.
2. Don't ask me for source code as you did. I don't know your environment, your processor, the motor
driver, etc. Post your code and tell us where it fails. Accurate questions, please!