Re: [Lost Steps
Posted by
beer@s...
on 2000-08-23 08:47:17 UTC
On 23 Aug, CAD_CAM_EDM_DRO@egroups.com wrote:
agree upon, this is fact, plain and simple.
But to add a couple of refresher points to clarify this ...
1. "Wire" is a theoretical thing, that does not exist in nature. The
stuff we call wire, the stuff we use to "wire things up", is always a
complex thing, exhibiting resistance, inductance, and frequently
capacitance.
2. There is only ONE ground point in a circuit. All other parts of the
circuit connected to this point are not quite at ground, because of #1
above.
3. The engineer who designs any particular circuit hopefully takes this
real world into account. Engineers who design circuits with high gain
and/or high currents MUST take this into account, again, because of #1.
This board has both high gain and high currents.
Which leads us back to the single point ground. All of the various
ground points in the system MUST go back to a single point, and that
single point should be the negative terminal of the main filter cap.
There is an argument that can be made that the negative terminal of a
bridge rectifier is more negative than the negative terminal of the
filter cap, but a close examination would show that under high
instantaneous current conditions, that point might actually be
positive with respect to the cap. At any rate, bringing ALL
ground connections back to the cap's negative terminal will solve
grounding problems.
That means that bringing a "wire" from the power supply end of the
board as well as a "wire" from the logic end of the board back to the
filter cap. Also, the "ground" wire(s) from the input connection ( from
the parallel port ) must also go back to this single point.
I don't think that noise is the problem. With all due respect to those
who have suggested cures for noise problems ( and most of those cures
can't hurt ), I think this is the wrong track. The inputs to this
board are active low, and are pulled high by a resistor ( 1k? ). It
would take a HUGE amount of noise to force that pullup to ground ( OK,
<1/2 Vcc ) and thereby create a step pulse, and none of that noise
would exist at any level with the unit in steady-state, i.e., not
stepping.
Alan
--
Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta
>Agree wholeheartedly with this - actually, there is really nothing to
> If you don't want to have a system plagued with noise problems, do
> the ground wiring right from the beginning. Right means use the
> concept of a "holy point ground". This means ALL ground wires are
> returned to a single point; power supply ground, motor drive ground,
> parallel port ground, in short if it has a ground wire, take it to
> that point! If shields are used, take them there too.
agree upon, this is fact, plain and simple.
But to add a couple of refresher points to clarify this ...
1. "Wire" is a theoretical thing, that does not exist in nature. The
stuff we call wire, the stuff we use to "wire things up", is always a
complex thing, exhibiting resistance, inductance, and frequently
capacitance.
2. There is only ONE ground point in a circuit. All other parts of the
circuit connected to this point are not quite at ground, because of #1
above.
3. The engineer who designs any particular circuit hopefully takes this
real world into account. Engineers who design circuits with high gain
and/or high currents MUST take this into account, again, because of #1.
This board has both high gain and high currents.
Which leads us back to the single point ground. All of the various
ground points in the system MUST go back to a single point, and that
single point should be the negative terminal of the main filter cap.
There is an argument that can be made that the negative terminal of a
bridge rectifier is more negative than the negative terminal of the
filter cap, but a close examination would show that under high
instantaneous current conditions, that point might actually be
positive with respect to the cap. At any rate, bringing ALL
ground connections back to the cap's negative terminal will solve
grounding problems.
That means that bringing a "wire" from the power supply end of the
board as well as a "wire" from the logic end of the board back to the
filter cap. Also, the "ground" wire(s) from the input connection ( from
the parallel port ) must also go back to this single point.
I don't think that noise is the problem. With all due respect to those
who have suggested cures for noise problems ( and most of those cures
can't hurt ), I think this is the wrong track. The inputs to this
board are active low, and are pulled high by a resistor ( 1k? ). It
would take a HUGE amount of noise to force that pullup to ground ( OK,
<1/2 Vcc ) and thereby create a step pulse, and none of that noise
would exist at any level with the unit in steady-state, i.e., not
stepping.
Alan
--
Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta