4 stepper motor control circuit- help!!!

Here is a schematic of the circuit designed by myself for controlling 4 stepper motors through the parallel port . though this circuit is simple , it does not seem to work !!!

could anybody PLEASE:

1 . check the drawing for fundamental errrors.
2 . transistor 2n3055 does not bias
3. input is 12 volts 5 amp regulated by 8 - 7812 ics
4. voltage across sl100 is 2.5 volts

also could anyone please clarify whether there will be any voltage drop across the 7812. i seem to get only 8 volts after rectification. the rectification circuit is made of 4 - IN4001 diodes in a bridge.

thanks in advance,


D.ajay kumar
m.tech (mechatronics engg.)
Vellore Institute of Technology
india 18/03/04**broken link removed**

The drivers for the 2N3055's are shown as PNP, is this correct?.

If so they can't ever be switched on, to do so requires their base's pulling down to ground - there's no way to do that on your circuit.

2N3055 is an NPN device...

Are you planning to run the motors seperately, like on there own??

This wouldn't work, only one data bit (0 to 3) can be allowed to be turned on simultaniously (spelling?) . You can have as many bits turned on in data bits (4 to 7), but only one data bit between 0 to 3 can be on at once.

If 2 or more data bits (0 to 3) were on, 2 or more windings in each motor would fire. This isn't good.

hope this helps.