I recently played around with this.
try putting resistors going to the base, you may be overdriving them and the
PORTB pins.
Also, if you have tried to swap emitter and collector, you may have blown the
transistor.  Also, since all the current in a transistor flows through the
emitter, have your stepper motor wire connect to that, and then going to ground
(for an NPN) or + (PNP)

Greg Hastings wrote:

> Hi,
>
>   I am still fairly new to electronics and have a pretty basic question on
> using the PIC to controll stepper motors.
>
>   I wrote a simple program to send out the pulses and I did get a motor to
> turn but it turns very weakly.  My guess is that the PORTA voltage levels
> are too low.  I have heard one can use transistors and a separate larger
> voltage level to increase the power of the motor.
>
>   So I added four 2222 NPN transistors w/ the base of each connected to the
> PORTA.0 - PORT.3 bit outputs.  I had +9V from a wall wart going into the
> emmitter and then the collector was connected right to one of the motor
> inputs.  With this addition to my circuit the motor does not turn at all.  I
> have also tried swapping the emmitter and collector but that fails as well.
> Anyone know why this is so?
>
> Greg (ghpic@hotmail.com)
>
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