L297/L298 Help. Please :)

The chip will quickly turn the coils on and off to limit current when the
voltage on the sense resistors shows that the stepper is drawing too much
current.  It turns it on and off at the chopper frequency (14 KHz for you).
But there are two ways it can do it.  This is what the control line
selects.  It either pulses the inhibit lines (when the control signal is
low), or it will pulse the drive lines (when the control signal is high as
you have it).

When it pulses the drive lines, it does it setting both sides of the coil
to high, instead of both to low.


I don't know if it makes any difference which way the control is set.  If
you are driving the L298N I think either should work from the way I read
the spec sheet.  If you are using some other circuit for driving the
stepper, then you might want to do it one way vs the other.


Not needed.  But a square wave with a 50/50 duty cycle is fine.  It's an
edge triggered signal which means the stepper should advance to the next
position on the rising edge of the signal.  It's only important that you
hold it low for at least .5 us before letting it rise again.


I would suggest you create a debounced switch to drive the clock input so
you can manually step it (or maybe drive with your PC, but make it on do
only one step).  Does the stepper advance correctly when you do this?  Does
the CW/CCW control make it correctly step one way or the other?

If not, measure the voltage across each coil and the outputs of the chip
and see if everything is as it should be.

Also, you did not mention how you have the half/full input set.  That took
me some time to understand.  If you use the full step mode (input low), it
will produce one of two different output sequences depending on what part
of the sequence the chip was in when you selected the full step mode.  In
half step mode, it does the same thing always.  I would suggest just
connecting the pin to +5 for half step mode until you figure out what's
going on.

What it is doing in full step mode, is just using the half step sequence,
and skipping every other step.  So depending where you start, it will
either only use the half steps (where both coils are energized at the same
time), or it will only use the full steps, where only one coil is energized
at a time.

If you try to make the motor step too fast, it will just vibrate instead of
spinning.  Cold that be your problem?

Also, are you sure you are using a bipolar stepper (4 wires (not 5 or 6))?
Do you have the wires connected correctly?  If you invert a coil, it makes
no difference, because it just makes it spin the other direction. But if
you swap wires so that one coil is connected to A D and the other to B C,
it won't spin correctly but it will buzz.  Just take the stepper out of the
circuit and measure the resistance of the wire pairs to make sure you know
which wires go to a coil.

--
Curt Welch                                            http://CurtWelch.Com/
curt@kcwc.com                                        http://NewsReader.Com/