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  #1  
Old Wed 26 April 2006, 11:02
Gerald_D
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Parallel Port breakout - getting the signals from the PC to the drivers

In this thread we saw the "drivers" and saw that they needed signals. The Mach software puts out signals on the parallel printer cable. This is a way of connecting from the printer cable (bottom right) to the drivers (top):




Apologies for the general mess! A lot of the wires in the picture are for getting a spindle to behave itself.

The printer cable enters a "breakout card" on the right, in this case a PMDX-120. (But I have switched to PMDX-122 now - May '07) From the top edge of the breakout card there is a grey 3-core cable to each of the drivers. At this point one has enough connections to actually turn the stepper motors from keyboard commands.

The other black wires from the top of the breakout card are for limit switches, E-stop, Z-zero plate, etc. The connections at the left edge are from relays to turn on/off router/spindle/dust collection/vacuum etc.
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Old Thu 22 June 2006, 13:05
Patrick Toomey
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Gerald,

I'm starting to design my Gecko/Mach controller for my ShopBot and I have a question for you. I see that the PMDX-120 is a 4 channel card so that would handle my X1, X2, Y and Z drivers. I also run a spindle so I would need a 5th driver. Could I go with 2 PMDX-120's hooked up to 2 different parallel ports? If so, would Mach 3 be ok with that and be able to use the second port for the 4th axis (indexer)? Would there be an easier way than this, such as driving two Geckos for X1 and X2 from one of the PMDX channels and just reversing the step direction on one of them?
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Old Thu 22 June 2006, 14:02
Gerald_D
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Hi Patrick

Two PMDX-120's hooked to two parallel ports will double the number of outputs/inputs, and Mach3 can handle this.
But, you don't need a "5th channel" to drive a "spindle". A spindle is actually a remarkably dumb device and all you need is a on/off relay to start/stop the spindle. (The speed of the spindle is controlled by the VFD - it is possible to have Mach3 control the spindle speed, but it is not typical). The "MechMate" has a spindle and that single PMDX-120 seen in the pic above is controlling the whole system.

However, for "MechMate 2", I have gone for the PMDX-122 as opposed to the PMDX-120 because I discovered how important the "charge pump" feature is...... You must have seen what happens when you have a live printer plugged into a PC and you reboot the PC - the printer often gives a kick or prints a random character. During the booting of a PC, it often puts out junk on its parallel port. We found out the dangerous way what effect this has......

Sean was busy changing a bit on the spindle. At the same time, I was in another corner of the shop and tripped the power and then switched it back on. The MechMate PC re-booted automatically because of the power interruption - and it sent a random signal to start the spindle, flinging out the wrench! The "charge pump" prevents this. We have actually built a charge pump for the PMDX-120 and it explains the lone wire going to one of the parallel pins in the photo above and the masking tape label on another hacked part of the board.

Before I confuse you too much, how much control over the spindle do you want Mach3 to do? Just the normal start/stop, or something more elaborate?
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Old Thu 22 June 2006, 14:09
Patrick Toomey
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Gerald,

Oops, I keep mixing my terminology, I do have a spindle that I want to control start/stop and preferably RPM's but what I meant to say is that I have an indexer that I need to use as a 4th axis.
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  #5  
Old Thu 22 June 2006, 23:44
Gerald_D
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Ah, that makes more sense now

I once explored the issues of driving the two x-motors off the same channel and the official technical response was that it is quite easily do-able. Either two Gecko's from one channel, and even 2 low-current motors from 1 Gecko. But, special conditions apply and best you check those with the suppliers.

Mach3 has a facility for squaring the gantry using separate limit switches for the 2 x-motors. You will lose this if you combine the motors onto one channel.

I am not up to date on spindle speed control via Mach3. It is something fairly popular with the metal-cutting guys who do things like threads. I think they have a frequency to voltage converter after the parallel port and the VFD reads the voltage level.

From what I read of the G100 from Gecko, that will make a parallel port system fairly obsolete. And it will give you lots of "channels". But, until that is fully ready, I think you need a pair of pair of PMDX-120's

However, The way in which I use the PMDX-122 with my spindle, I still have a pair of outputs doing nothing. Maybe they could step/direction an indexer? I am out of my depth here.....
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  #6  
Old Fri 23 June 2006, 07:37
Patrick Toomey
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I read up on the PMDX 122 and that's definitely the way I'll go. I didn't know about the charge pump option but that makes a lot of sense. That could be incredibly dangerous without that. I was looking at the G100 which looked awesome but a little too experimental for now since I do need my machine for production work and can't afford big downtimes.

I'll figure on 2 PMDX-122's so I'll be sure to have plenty of inputs and outputs. I saw on another thread that you are going to have pause and resume buttons. Can you just specify in Mach3 which inputs should correspond to which actions? I'm thinking if that's the case maybe I could rig up a remote pendant with jogging and fixed stepping buttons? There are many times when I'd like to be close to the spindle moving it to a position to start cutting. Right now I have to keep walking back and forth between the computer and where the spindle is which is a real pain.
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  #7  
Old Fri 23 June 2006, 08:41
Gerald_D
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Mach3 can handle a lot of customising, and remote pendants with "MPG's" have become all the rage. A MPG is a manual pulse generator, or a small handwheel that makes pulses as you turn it. Some guys are supplying pendants that connect to the serial port, I think? The main source of info for all this is the Yahoo Mach support forum.
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