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  #1  
Old Sat 28 October 2006, 04:42
Gerald_D
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PMDX parallel port break out card for the MechMate

You will need 1 of these PMDX-122 parallel port "break out" cards from PMDX.

Similar cards also available from Campbell Designs and others, but my experience is with the PMDX-122.

If you are using a ready-packaged control box, you do not need this card.

If you are heading for more inputs and outputs that just the very basics, then you need 2 of these cards.
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  #2  
Old Thu 09 November 2006, 00:28
Gerald_D
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Our board is jumpered as per this diagram:



Notes:

1. We use Gecko 202's. If you are using the G203 then JP1 must move down. (see small attachment at bottom)

2. None of the terminals marked GND may be connected to metal parts, or the common ground point of the rest of the system in the control box.
Attached Images
File Type: gif 001.gif (3.3 KB, 3828 views)
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  #3  
Old Wed 17 January 2007, 20:45
fabrica
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Gerald, The Wiring of the control box is almost complete. Can please explain to me in simple lannguage as to how the (PMDX) breakout card and the stepper drivers are to be wired. Specially I need to know as to how the two steppers on the x axis are made to rotate in opposite directions . . . . .

In the picture of the PMDX card I see only three wires going from the card to the drivers.
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  #4  
Old Wed 17 January 2007, 22:25
Gerald_D
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The picture above is correct - there are only 3 wires each. (one place (pin 7) on the Gecko is not connected). Put the jumpers in the right places. Give power to the PMDX. To be safe, read and understand the documentation for
the PMDX and Gecko.

If you need to reverse the direction of rotation of a stepper motor, you need to reverse one coil only. The easiest way to do this is to reverse a pair of connections (swap) at the Gecko. (Only do this if the Gecko is dead, or else you might kill it). I suggest you swap pins 5 and 6.


Remember to install the correct resistor across pins 11 and 12.

The synchronising of the two x-motors is done in Mach. The name of the second X-motor in Mach is the A-axis. Look in the Mach documentation on how to "slave" the a-xis to the x-axis. On the screen you will see this:

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  #5  
Old Wed 17 January 2007, 22:56
fabrica
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Thanks Gerald, I feel that the info provided would be sufficient for the moment. I will contact you again if the necessity arises.

Somehow I need to make sure that I get this baby moving today. My patience is running out.
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  #6  
Old Wed 07 February 2007, 08:59
reza forushani
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What do you guys think of the motherboard board/breakout board and power supply board from PMDX?
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  #7  
Old Wed 07 February 2007, 09:50
Gerald_D
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Reza, I think this question is a duplicate of the one answered here? This is good place to discuss it if you need more info - let us know.
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  #8  
Old Fri 02 March 2007, 07:44
Kim Mortensen
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I just checked in at PMDX and found this little baby, this is nice, I'm thinking of getting this for my machine instead of the 122 board.
No more getting those wires wrong... :-D

http://www.pmdx.com/PMDX-131/index.html
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  #9  
Old Fri 02 March 2007, 10:42
Gerald_D
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See a little discussion in Reza's thread. link
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  #10  
Old Fri 02 March 2007, 11:00
Kim Mortensen
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Yes I see he says it does not have a charge pump, but if you check the description on PMDX homepage, then it clearly says it has the charge punp...
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  #11  
Old Sat 03 March 2007, 11:49
Gerald_D
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Mike, what do you think of turning some wire through the toroid (DIY-ourselves) to power the PMDX-122 directly into its 9V AC input option?
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  #12  
Old Sat 03 March 2007, 20:21
Mike Richards
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Gerald,
I'm sure that would work. So far, I have never wound a toroid, so all I know is what I've read. The difficult part would be knowing how many 'turns' to wind. I suppose that you could wind a dozen turns, connect a meter to the new turns, turn on the power, and see if there is any voltage. Assuming that there would be some reading on the voltmeter, it would just be a process of turning off the power, and winding some more turns until you had the desired voltage.

(There are a number of warnings about keeping the windings tight, using tape, etc. on various web sites. I have no idea whether they're valid or not.)
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  #13  
Old Sat 03 March 2007, 20:47
Gerald_D
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It is 5:45am coffee time here now - day is breaking. Looks like a little experiment is called for today.....
(James Webster reminded me of this option)
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  #14  
Old Sun 04 March 2007, 02:15
Gerald_D
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Grabbed a 500VA toroid, looped 12 turns of wire, and got a steady 6.6V from it. Havn't got long enough thin insulated wire here at home, but it is very obvious that this is an easy option to power a PMDX-122. The little grey block transformer I am using now is nominal 9.5V, but actually puts out 11.5V no load because the magnetic core is so minimal. Winding around the huge toroid will be much better than a separate small transformer....and it solves mounting and space problems.
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  #15  
Old Sun 04 March 2007, 02:36
Gerald_D
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When I bought that little no-name brand 9V transformer, I had this discussion with Steve Stallings at PMDX:

I have just learnt that a nominal 9V transformer in the 2VA range has an off load voltage of about 1.35 times higher than when fully loaded. I was going to ask for a better transformer this morning, after measuring 11.4V at the output terminals, and 11.2V when connected to a "naked" (nothing connected) PMDX-122. The sales guy hauled out a couple of supplier's data sheets and showed me that this behaviour is typical for transformers in this range.

Can I carry on using this transformer?


The 8 - 10 VAC supply should work OK. We had allowed
lower voltage supplies earlier and most worked, but a
few were weak, so we said 9 VAC. Greater just creates
a bit more heat in the regulator. We didn't want people
using 12 VAC, so that left 9 VAC as the only commonly
available value.
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  #16  
Old Tue 27 March 2007, 20:49
christipher saint denis
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On close examination of my new PMDX-122 I discover that my printer cable does not fit into the PMDW-122 printer cable slot.

I now realize PMDX-122 requires a standard IEEE-1284 Centronics style printer cable. PMDX sells a "26 pin ribbon cable which allows a remote DB-25 to be use".

When I order the break out card I did not realize my printer cable was a DB-25 cable. Should I now order the $5 "PMDX-DB25Ribbon" accessory or will an db-25 to male centronic 36 adaptor work.

Thanks for your time.
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  #17  
Old Tue 27 March 2007, 22:24
Mike Richards
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Christopher,
One end of a 'standard' parallel printer cable has a 25-pin male connector on the PC end and a centronics connector on the printer end. You would have to verify that the proper pins are connected on each end of the cable if you buy something else. The $5 PMDX cable did not work for me. Unfortunately, I don't remember whether it was the polarity of the connectors or something else. After a few months of having it just sitting on the shelf, I tossed it out.

Right now, I have two PMDX-122 boards that I drive using 'standard' parallel printer cables.
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  #18  
Old Tue 27 March 2007, 23:31
Gerald_D
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Christipher, I find it very strange that your normal (parallel) printer cable did not fit the slot....

- Do you have a "parallel" printer cable? (A USB cable will not work. A modern laptop PC without a parallel port will not work either)

- Have you tried to turn the connector upside down?

Until you have a clear answer on the above, it will not help you to buy another cable from PMDX.

I am guessing that I did not make it clear enough that the PC you use for MechMate must be the "old-fashioned" type with the big parallel printer connection and fat cable. Modern laptops no longer have this connection, but most desktop PC's still have them or can be fitted with them.
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  #19  
Old Wed 28 March 2007, 00:05
Gerald_D
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You have prompted me to start this thread.
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  #20  
Old Wed 28 March 2007, 10:15
christipher saint denis
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Thanks for the info. The cable I had on hand was one that came with my taig cnc. It has male DB-25 to female DB-25. I will go grab a 'standard' printer cable.
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  #21  
Old Wed 28 March 2007, 11:29
Gerald_D
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Glad to hear that your problem is simpler than I thought. Anyway, it was a good reason to start a thread on computer port requirements. Thanks
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  #22  
Old Mon 14 May 2007, 08:53
Gerald_D
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The PMDX-122 requires a nominal 9V AC input, but small transformers measure a lot higher when there is little or no load connected to them

I asked Steve Stallings of PMDX a year ago:

I have just learnt that a nominal 9V transformer in the 2VA range has an off load voltage of about 1.35 times higher than when fully loaded. I was going to ask for a better transformer this morning, after measuring 11.4V at the output terminals, and 11.2V when connected to a "naked" (nothing connected) PMDX-122. The sales guy hauled out a couple of supplier's data sheets and showed me that this behaviour is typical for transformers in this range.

Can I carry on using this transformer?


His reply:

Yes, that is normal for small transformers and we try to take it
into account when specifying units for the PMDX-122. After
the PMDX-122 has been running for 10 minutes or more,
feel the heatsink. To assure a significant load, try to turn
on the relay. If you can touch the heatsink and count to 10, then
it is not too hot and the transformer is OK even though the voltage
is high. If it runs too hot, no damage to the PMDX-12 will occur
but the overtemp shutdown of the regulator would cause the
control signals to do strange things.


Then:
Thanks Steve, I will use a popular local transformer that is nominal 230V/9.5V rated 2VA
Regards, Gerald


He replied:
The nominal 8 - 10 VAC supply should work OK. We had allowed
lower voltage supplies earlier and most worked, but a
few were weak, so we said 9 VAC. Greater just creates
a bit more heat in the regulator. We didn't want people
using nominal 12 VAC, so that left 9 VAC as the only commonly
available value.


Well, we passed the touch-the-heatsink-for-count-of-ten test and a year later we are still fine.
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  #23  
Old Thu 07 June 2007, 23:21
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Following on from this post in a power supply thread, Steve Stallings posted this reply at the Gecko Yahoo forum:

The Step, Direction, and Common pins of a Gecko
driver are isolated from the power and motor leads.
If you provide power to a breakout board that does
not share a common ground with the power to the
Gecko drivers, then you maintain this isolation.

For safety and noise reasons, it is traditional to
connect the negative side of the power to the Gecko
drivers to the case of the box containing the Geckos
and also to the machine frame ground.

To maintain isolation, the ground from the computer
(the ground in the parallel port cable) must not be
connected to the box containing the Geckos or to
the machine frame. If you are using a metal shell
DB-25 connector you will need to isolate the metal
shell from the box. This also applies to the ground
side of control outputs and status inputs (home and
limit switchs) if the breakout board does not provide
isolation of these signals. The PMDX-122 provides
buffering, but not isolation, so you should not
connect the ground side of any home or limit switches
to the control box or frame ground. If you are using
a PMDX-131, a PMDX-120, or any other board that does
provide isolation of these signals, then you can
tie the ground or commons on the isolated side of
the interface board to the control box or machine
frame ground if desired.

If you violate these rules, you will probably create
a "ground loop". At a minimum you will provide an
easy path for noise to enter the system. At the worst,
the ground of the outlet powering the computer may
have many volts of offset from the ground attached
to the frame of the machine and the resulting current
from trying to short this voltage through the ground of
the parallel port cable may damage the computer, the
interface board, or both. I have seen as much as 40
volts between grounds of outlets on different circuits
in a modern industrial building.
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  #24  
Old Tue 09 October 2007, 11:28
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Gerald....you are wise and full of great information. I am so glad your out lurking in the other forum's as well.
I have my answer.....use a single pmdx and share the channel. That will leave the 4th axis available for the indexer if I add it later.

Thank you again.

News for another thread....based on the G100 status of killing rabbit modules, I will not be using the G100 this machine build.

Thank Gerald! Sean
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  #25  
Old Tue 09 October 2007, 11:55
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The G201 and G202 drives weren't that good on a single "channel", but since you have a call in to PMDX, verify it with them (actually Steve Stallings)
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  #26  
Old Tue 09 October 2007, 18:19
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Gerald,
I had a very nice chat with Mr Stallings this afternoon. He did verify that it is "plausible" to split the channel and run 2 steppers, but advises against it if you have the $ to afford a second card. The Mach can easily address a second pmdx to use the additional channels at a very low cost. For the sake of "i will sleep better at night" and Mach to be able to verify and have control of the x axis with error correction, I am going with the option of building my cabinets with enough room to double stack the PMDX BOB for the addtional axis control. *essentially, long standoffs to vertically stack the boards.*

I will eave room on the heat sink for an additional drive as well. Small price to pay for future expansion if I need it.

Thanks for the great input.


Sean
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  #27  
Old Tue 09 October 2007, 21:30
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Sean, test the dual-PMDX setup carefully before installing it. I tried using two cards for a while on my test bench and they greatly expanded the I/O capabilities of the controller; however, when I tried to run steppers on both cards, the motors ran rough. 'Scope traces showed a ragged pulse train compared to running a single card. My setup used the highest pulse rate (45K at that time). That was about two years ago and there have been many revisions to Mach 3 since then. (And there is also the very small possibility that it might have been my fault.)
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  #28  
Old Wed 10 October 2007, 04:30
Dirk
Just call me: Dirk
 
Alpharetta, Georgia
United States of America
Gerald
I was wondering the problems that "weren't that good"? Was it simply the electronics was marginal to push 2 drives, or something else. I've never had problems driving several geckos off one channel.
Dirk
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  #29  
Old Wed 10 October 2007, 04:40
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Dirk, I think the problem is the relatively high step/direction signal current requirements for the G201 and G202 stepper drivers. Those two stepper drivers require a minimum of 15mA to drive the opto-couplers. Fifteen milliamps is a hefty load for some breakout boards. (I always buffer the signal with an additional logic chip when I use a common signal to drive more than one stepper driver.) Although I haven't tried driving two G203v stepper drivers from a common signal, they should work without buffering, since the G203v only requires 2.5mA to work properly.
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  #30  
Old Wed 10 October 2007, 06:07
Dirk
Just call me: Dirk
 
Alpharetta, Georgia
United States of America
I use seperate gates also, I thought there might be something else I haven't caught yet.
Dirk
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