Thanks for all the useful information!

To turn "on" the PNP transistor, the base has to be at least 0.6V less
than the emitter (and also a small current needs to flow) right?

So if my active low signal goes between 0 and 5V...and my motor power,
which is connected to the emitter is 5V, then I'm set.
What if my motor power was let's say 9V?  Does that mean, even though
the microcontroller is holding the pin at 5V, the transistor would
still turn on, because the emitter is at 9V and the base is at 5V?

-James

On Apr 30, 2004, at 7:59 AM, Paul James E. wrote:

>
>>>>>>>>>>>   I would use a PNP transistor with the emitter connected to
>              +v on the external power supply.  Connect one end of the
>              motor to the collector of the transistor, and the other
> end
>              of the motor to ground.  Connect the active low pin to the
>              base of the transistor through a 500 ohms or so resistor.
>              The way this works is when the unit is powered up, the
> active
>              low output will come up high.  The motor will be off.
>              When the active low pin goes low (active), the transistor
>              turns on and supplies power to the motor.

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