You need to establish the DC resistance of your motor and hence its stall current. See my reply #28. If the stall current is less than about 500mA, you can use a transistor to control the motor speed. If it is more, you should use a mosfet.
You need to establish the DC resistance of your motor and hence its stall current. See my reply #28. If the stall current is less than about 500mA, you can use a transistor to control the motor speed. If it is more, you should use a mosfet.