Re: ATM motorizing scope questions

["Bob May" <bobmay@nethere.com>]

Sounds like you may have it running.  Go back and check to see if all the
connections are right.
The sound you are hearing is the frequency of the stepping of the motor and
should be a quiet hum at the worst if the circuit is wired right.  As the
speed goes up, that frequency will go up until you get to the point where
you can't hear it anymore as you ear won't be able to detect the high
frequency.
I don't know how big of a motor you have and how hard you are trying to stop
it - some people consider a particular torque to be light while others
consider it difficult to stop.  Finger friction has some to do with this and
I'll note that different individuals have widely different basic coefficient
of friction in their fingertips.  It may also be that the current to the
motor is low for some reason (probably a low voltage) and the motor is
showing that in the lack of torque.
The wiring of electronic circuits is, unfortunately, not only a chore of
getting the parts together in the right arrangement but often, especially in
higher power circuits, also in the physical arrangement of those parts on
the board so that the ground and power lines don't get modified by those
current needs of each part.  The thing that many beginning electronics types
forget is that everything has a resistance, an inductance and a capacitance
and that often needs to be taken into consideration.  On a circuit of which
you have built, the inductance and capacitance isn't much but the resistance
of the copper wires can be.  In other words, the wires from the battery to
the motor's power control transistors needs to be substantial enough to do
the job and, at the right point at/closer to the battery, the control
electonics gets its power from the power wires.
Good luck and have fun with electronics!
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net