Re: [CAD_CAM_EDM_DRO] Re: The mechanical part of my router is done!

On Fri, 18 Jul 2003 09:55:25 -0500, you wrote:

>OK, guys...I need a little bit of help. Who's good with electronics?
>
>I have bought 3 stepper controller boards -- they are based on the
>L297/298 chipset, and run my motors very nicely. The down side is that
>they have an on-board pulse generator -- no hookup for a parallel port.
> Which means...modifications!

True.

>
>Here's the schematic for the board -- it's a surplus board from TI.
>http://makeashorterlink.com/?V59F32F45

on screen

>
>As I see it, I need to bypass the 555...cut the lead between pin3 on
>the 555 and pin 17 on the 297, which is step input. And I need to hook
>into pin 18 on the 297, which is direction. Of course it didn't work
>like this, which is why I'm asking for help.
>

Actually, that's about what it should do.

>Assume nothing -- I've played with serial ports, but I'm not sure about
>parallel interfaces -- does anything need to be tied to ground, a state
>or enable pin tied such that it is active, etc?

Not for the port, no, but there are some things to do.

1) most interfaces want to see step and direction, I'd rewire for
that.

2) the opto isolators are just used to convert logic levels here, not
for isolation.

to convert to step/direction:

1) break the wire connection between the internal 5 volts and R1, R2,
and pin 7 of OCA. Break the connection to pin 8 of OCA, and to pin 7
of OCA.

Imagine a 5 volt supply (separate!) on OCB going to the left end of
R2. (this feeds the CW terminal). the ground of that supply will go
to one of the ground pins on the 25 pin parallel port connector. Do
not wire to chassis or anything else. TB1-5 can go to pin 2 on the 25
pin connector. Pin 2 can be set as an output in turbo cnc (I'd
recommend it). You are using the 5 volts from the power supply to run
the diode in the optoisolator. Since OCB is wired the way we want, we
leave it just as is.

Wire OCA the same way, removing CR10. Ground pin 8. Run Pin 7
through a 10 k resistor to the board's 5 volts. Then run pin 7 to pin
18 on the l297. Be certain you disconnect the lead going to pin 3 of
the 555.

OCB and OCA should electrically look the same.

With no common ground connection, and a separate 5 volt supply, this
board will now work on step/direction for the motors.

I would suggest pins 2 and 3 for the inputs to the board from a db25
(25 pin) connector. Use an IEEE cable, one that has all 25 wires.
Grounds are anything between 18 and 25.

>
>Now, all of this, I can do (though maybe with some help from you
>guys)...is there any real danger of blowing something out?

All these mods will take is a bit of patience and a 5 volt supply.
Rshack ought to have one, make certain that it is wired so that you do
not have any common point to the board supplies. we are talking total
isolation (as much as possible here).

> I live in a
>TINY town, and having to build a breakout board, or something similar,
>would add in a week's delay, just because of the unavailability of parts
>in this area.

All you need is the supply.

IF you have the whole thing running off an existing 5 volt supply, and
you can totally isolate the regulator vr1, or just duplicate it, then
you can get the 5 volt supply you need with a 9 to 12 volt wall wart.

Remember, total isolation, not even a common ground. You will have to
feed the board from a separate 5 volt supply, though.

>To be honest with you all, I just want to see my motors
>spin under computer control! Down and dirty hacks are fine, at this
>stage of the game.

This isn't really dirty, and should cover all of it . Heck, you could
even use batteries for the 5 volt supply, 4 nicads would work fine.
(don't exceed 5 volts, just because.... it is a parallel port...)

>
>HELP?!

See if all this makes sense.

Harvey

>
> -- Chuck Knight
>
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