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Author Topic: Mach3 / PMDX-122 Issue  (Read 493 times)

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Offline reuelt

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Re: Mach3 / PMDX-122 Issue
« Reply #30 on: March 20, 2019, 07:24:31 AM »
I think PMDX sells a opto-board calls PMDX-105 to "PATCH UP" for the PMDX-122 lack of opto-isolation.

Years ago, I saw on ebay a Canadian company selling BOB with extra wires that jumps over the opto-isolation - claiming that the BOB were otherwise faulty.
(They just MISTAKENLY did not connect a 12V supply for the opto-isolation chips).

Some even make videos on youtube WRONGLY "teaching" people how to solder jumper wires.
"the gift of God is eternal life through Jesus Christ our Lord"
Re: Mach3 / PMDX-122 Issue
« Reply #31 on: March 20, 2019, 01:08:14 PM »
Hi,

Quote
I think PMDX sells a opto-board calls PMDX-105 to "PATCH UP" for the PMDX-122 lack of opto-isolation.

Why bother, this BoB has worked for years in this configuration.

Craig
My wife left with my best friend...
     and I miss him!

Offline reuelt

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Re: Mach3 / PMDX-122 Issue
« Reply #32 on: March 20, 2019, 05:28:28 PM »
Hi,

Quote
I think PMDX sells a opto-board calls PMDX-105 to "PATCH UP" for the PMDX-122 lack of opto-isolation.

Why bother, this BoB has worked for years in this configuration.

Craig

New version PMDX-122 (REV D) now has a Charge Pump - it is for added SAFETY to prevent machinery motors from moving UNTIL operator using MACH3/4 is FULLY in control.
PMDX-105 optional card is to provide Opto-isolation so that limit/home switches can optionally operate on higher voltages (e.g. 12V or 24V) instead of just TTL level of 5V.
Advantage of higher voltage limit/home switch is that HF noise from VFD & steppers for example will be less likely to falsely trigger the limit switches. HF noise or spikes will have to swing higher voltages to falsely trigger limit switches running at 12V or 24V  instead of 5V.
Another advantage of Opto-isolation is to prevent PC motherboard or parallel ports BLOWING UP. Some companies e.g. Abililty Systems (maker of famous Indexer LPT) used to tell customers to plug in a PCI LPT card or 2 and not use the LPT port on motherboard so that if there is an input surge, you ONLY have to replace the PCI card and not the whole computer.
Opto-isolation prevents blowing up your whole computer or just your PCI/PCIe cards.

People can make their own decision based on more knowledge.

"the gift of God is eternal life through Jesus Christ our Lord"
Re: Mach3 / PMDX-122 Issue
« Reply #33 on: March 21, 2019, 01:34:17 AM »
Hi,
we should do some polling.

Quote
now has a Charge Pump - it is for added SAFETY to prevent machinery motors from moving UNTIL operator using MACH3/4 is FULLY in control.

I am well aware of what a charge pump is and what it does and guess that most understand it also. I have never used a charge
pump with either Mach3 and parallel port or Mach4 and ESS, without problems. This comes in large part as a deliberate
design choices on my part that all potentially dangerous (when uncontrolled) motors and pumps are naturally in the OFF
state should the controller be out of service.

My guess is that 3/4 of all Mach users do not use a charge pump. Once upon a time yes is was the norm....not so today.
Would be worth doing some polling.

Quote
PMDX-105 optional card is to provide Opto-isolation so that limit/home switches can optionally operate on higher voltages (e.g. 12V or 24V) instead of just TTL level of 5V.

I certainly agree that optos allow an increase in flexibility, being able to use 24V devices is worthy of consideration.

Quote
Advantage of higher voltage limit/home switch is that HF noise from VFD & steppers for example will be less likely to falsely trigger the limit switches. HF noise or spikes will have to swing higher voltages to falsely trigger limit switches running at 12V or 24V  instead of 5V.

This is a widely held opinion but it is too simplistic to be accurate. The real determinant of noise immunity is not voltage
but impedance.

A 24V device may have a very high input impedance and therefore any inductive spike causes a substantial voltage swing
and potential interference with the signal of interest. The same circuit but at lower impedance with the same inductive spike
will have a proportionately lower voltage swing, ie less interference.

Thermal noise is described by Boltzmans equation:
P=4.k.B.T.R
P=noise power
k=Boltzmans constant
B=bandwidth
T=temperature (0K)
R=resistance (or impedance if reactive)

So for a given temperature and bandwidth, the lower the resistance, the smaller the noise power.

Have you wondered why so many electronic communication systems run at such low voltages? Take Ethernet for
instance, a voltage swing of less than 1V between a '1' and a '0'. That you might have thought that would render Ethernet
susceptible to noise yet in fact Ethernet is very noise resistant. The reason is the low impedance that Ethernet operates
at.

It is possible therefore to have a 5V TTL signal be as noise immune as a 24V signal IF the impedance is chose wisely.
For instance I do not like to load a 74LS TTL output more than about 10 mA, despite the maximum rating being 24mA.
By the same token I always like to load a TTL circuit such that an ON state current of at least 10mA, ie low to moderate
impedance for the sake of noise immunity.

Quote
Another advantage of Opto-isolation is to prevent PC motherboard or parallel ports BLOWING UP

Ok, yes you can blow up a PC by backfeeding the parallel port.......but when was the last time you heard of anyone
actually doing it? There again I think we should do some polling to find out. I know lots of people run scared but
I don't know anyone who has actually blown up a PC.

Hey, I usually have a good go at getting electronic stuff to go......but I have an AWSOME reputation for blowing stuff
up.....and I haven't managed to do so yet and I've got non isolated inputs and have done for five years.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mach3 / PMDX-122 Issue
« Reply #34 on: March 21, 2019, 08:59:38 AM »
SO...update on progress....Boss won't let me change any wiring on the board yet...He is of the opinion that it worked before, so it should work now ???

I explained to him that we're not necessarily "changing" anything....only unplugging a USB and plugging a round pin in to test and he still isn't budging.  Apparently he got a hold of the previous owner and is going to get his XML file to try before he'll let me swap the power supply.  Here's the kicker....apparently he was told you can't email the XML file. LOL.  So he's going to make a special trip to get the XML via USB on Saturday.  Whatever...I'm just a penny. Lol. 

I'll update once we have the XML....I'm kind of hoping it still doesn't work out of spite.  ;D

Thanks again for the help thus far!
"Failure is not an option, but the option exists"

Offline reuelt

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Re: Mach3 / PMDX-122 Issue
« Reply #35 on: March 21, 2019, 06:01:20 PM »
Ethernet is very noise resistant because the signal is a difference between the two twisted pair cables. Since noise will affect both twisted pair equally, the difference will remain the same. There is a differential circuit at each end.

USB, limits switches do not use "differential circuits". Noise will change the signal cable but not the ground cable.
"the gift of God is eternal life through Jesus Christ our Lord"