Re: Electronics gurus please help

> so experts: at a chopping frequency a couple 10Khz, could the pcb

layout have this much influence? i checked all the components, all
the connections, spent about 2 days on it, so i am 98% that the

> working and not working circuit only differs in the shape of the

traces.

>

At first guess I would say there is a small error somewhere on the
board yet or possibly faulty components due to assembly techniques.
10-20 Khz only requires decent board construction nothing real
special. If you are using any type of crystal these can be picky
about the stray capacitance on the board and may require changing the
load capacitors. The next logical place I would guess is the
comparator section as it is high gain, perhaps there is extra ground
noise or signal coupling on the new board perhaps it needs a few high
frequency bypass caps on the inputs. It is hard to visualize without
the diagram .

If you get really pissed you can buy a 3 axis unipolar chopper from
Paul Brewington for reasonable. I have one of these that seems to
work well , a micro stepper would be nice as this one is half step
only.

http://www.brewingtontech.com/

On the 6 wire motors since the windings are Bifilar (2 skinny wires
wound together on the same pole) you use the same amount of copper
driving it unipolar or half winding bipolar. In unipolar you switch
between one of the two skinny coils per pole where bipolar you simply
use the same skinny wire and reverse the polarity.

For the same drive voltage the performance between a half winding
bipolar chopper and the unipolar chopper seems roughly the same. I
have been working on a better test setup to compare the results but
on the observation level I see little difference.

At the same time the chopper drive does greatly out perform the
unipolar RL drive for speed due to the higher drive voltage and you
pick up more low speed noise. This is where the micro stepping would
be nice.

Brian
BSP