RE: [CAD_CAM_EDM_DRO] ADVICE SOUGHT INTERFACING ISSUE

> 1. Can I build up a little logic circuit on a board
> inside my HD case to drive the opto's in the 6410
> and power it using the old HD power supply in my
> case even though the logic inputs to the gates
> are coming from the PC (as long as I tie the COMMON
> from my box to the ground pins from the PC) or does
> this create some type of potential ground loop problem
> and a possible source for noise? If anyone wants to
> wax eloquent regarding ground loops and noise issues
> further, you would certainly have my undivided attention.
> I can bring out the +5 off the PC game port but it's not
> as clean as just having the one cable from the LPT port
> by itself also there may be additional logic, limit
> switches that need +5 and perhaps some Solid State relays
> I might add to my box later and I don't know what is
> left over from the PC's +5VDC supply after taking care
> of it's own business. Also I kind of like the idea of
> having some logic ahead of the opto's in the 6410 because
> I know what they can drive whereas I'm unsure what the
> current sourcing/sinking of the parallel port signals
> are.

building a circuit in your box will not be a problem as long as your circuit
is getting its ground reference from the PC's parallel port. A ground loop
may occur if your circuit ground is tied to earth ground and your PC circuit
ground is tied to earth ground. So you may want to tie your case to earth
ground (for safety) but keep your circuit isolated from the case.

now, from what I see in your drawing J1 is the actual connector to your
stepper drive. The stuff to the left of that seems to be provided as an
example and is not really part of the circuit. I don't know the current
specs for parallel port devices, so a safe bet would be to use a buffer of
some sort. Since TTL devices tend to sink more current than source and the
output from the parallel port seems to be active high, an inverter (7404)
would be a good choice. Simply substitute the inverter for the single input
NAND shown in the example.

> 2. If you look at the interface schematic referenced above
> two lines are shown terminating in thin air which make up
> the ENABLE function input for the 6410. I can show those here:
>
> | inside 6410
> ?___________ENABLED (collector) _____J1________ | -o 5Vdc
> | |----/
> | | / ---photo diode
> ?___________ENABLED (emitter) _______J1________ | -0 DRIVER
> ENABLED (NOT)
> |
> How do I provide the correct circuit and signal to these lines
> in order to produce the ENABLE signal? The signal out from the
> PC (and SuperCam) is ENABLE (logical high sourcing) and I want
> to feed this signal to all 4 motor drives simultaneously.
>

Don't sweat this one, this is an output that you could use to drive an LED
or something for a visual indication that the driver is enabled. From the
drawing I would gather that it reflects the state of the enable input (pins
3 and 8).

> ok ... 3 parts.
>
> 3. When I do the logic circuits, what are the best devices to
> use? TTL, Low power TTL, Schottkey TTL? I always remember TTL
> being very susceptible to noise especially when there are brush
> motors near by ... or am I just paranoid?
>

If the circuit you provided is correct then you may have to use plain TTL to
get the >10mA sink current for the step input. My specs show an LS at 8mA
max and a TTL at 16mA max. This would be another reason to build a circuit
to buffer the parallel port outputs.

Hope this helps!
Scott