CONTROLLER Part 2
by Fred Eady
Now that I have a Minebea
29SM-K series 1.8°-per-step
stepper motor shaft spinning
back and forth on the bench, I figured
it might be a good time to sit down
and tell you how I persuaded an
STMicroelectronics L6208PD to push
current through the Minebea’s stepper
motor coils. Unfortunately, I can’t provide
a visual play-by-play of my Minebea’s
alternately spinning motor shaft.
However, I can give you a description of
the hardware and software stuff you will
need to make your motor spin under the
control of an STMicroelectronics L6208PD
and a PIC18F2620 microcontroller.
Over the years, I’ve read thousands
of datasheets and application notes. To
this day, it is still a thrill to translate
the words of the manufacturers into a
functional device. In the previous SERVO
L6208PD installment, we walked around
the L6208PD with the intent of putting
the L6208PD to work with a stepper
motor and PIC microcontroller. All of the
preflight work we expended last month
will be applied to our goal this month of
creating controlled rotational movement
of a stepper motor shaft.
Spinning the Printed
SCREENSHOT 1. The idea is to provide as much heatsink area as possible for the
L6208PD. We also have to adhere to the L6208PD printed circuit board guidelines to
keep electrical noise to a minimum.
The beginnings of our L6208PD
Motor Driver Board can be seen in
Screenshot 1. I’ve used ExpressPCB as
the printed circuit board design and
layout program so that you can either
copy my printed circuit board layout or
use my original printed circuit board pattern as a basis for your own L6208PD
printed circuit board (PCB) design.
Note that the L6208PD Motor
Driver Board design provides a relatively
large heatsink area for the L6208PD on
the top side of the PCB. It’s a good idea
to physically bond the L6208PD’s
heatsink slug to the heatsink pad area.
So, as you can see in Screenshot 1, I’ve
included some top-to-bottom thru holes
under the L6208PD’s heatsink lug to
provide solder access once the L6208PD
has been mounted on its pads.
Before mounting the L6208PD, I
applied some solder paste to the
L6208PD’s heatsink lug. After completely soldering down all of the L6208PD
pins, I used a high-wattage soldering
iron applied to the bottom side heatsink
pad to flow the solder paste on the
L6208PD heatsink lug. I can tell you from
practical experience that this method of
mounting the L6208PD is sound.
While experimenting with the
50 SERVO 03.2008