>
>Do l need a separate power supply(battery) for the transistor? l tried the
>method above by using the same power supply(with the rest of the circuits)
>but it still cannot work well. l don't know what is the reason for this.

You may be crashing your power supply.
Try it with a separate supply, like AA batteries, for the motor.
In this case, series the batteries to get the proper voltage, and connect
the motor to the + battery lead. Connect the other motor lead to the
transistor's collector, and connect the transistor's emitter to the battery
- lead.

Connect a diode (1N4001 or similar) across the motor, with the banded end
connected to the battery + lead, and the other end to the transistor collector.

Connect the battery - lead also to the processor's ground, and connect the
transistor's base through a 1k resistor, to the appropriate port pin.

The 1k may need to be adjusted, it's just a guess.


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