Exactly what and how many/much...?

(I think I might have posted the original of this message in the wrong sub-forum. Sorry)

Hello,

Another newbie (relatively) enters, looking to learn a bit before I plunge again.
Background - I've done a few EMC controlled mini-mills in the very distant past but admittedly of the more simple type. (pre EMC2)
I can learn, but don't know much about electronics and honestly, I don't really have much desire to know much more
about electronics in general, but understand that I will need to learn more than I know in order to complete my next build.

I've a working Bridgeport CNC that I am thinking of converting.
It runs very well for me, but age, parts availability and price, and added capability are the motivators, here.
(is 3 axis and I'm thinking 4 axis minimum, 5 axis possibly)

Brushed servos, analog amps, power supply, PC are all good.
Everything is, actually, but I figure I'll be reusing those.

I'm looking at either Jon's PPMC or Mesa's cards.

Here's where the ignorance and confusion cripple me....

What EXACTLY does one need to accomplish thing, in completeness?
Is there some sort of checklist others have compiled over time with experience?

How many I/O spots do you need? How do you know? What constitutes one?
Does one need these opto isolators I read about? Why? What are they for?
Are they part of the cards that one buys or does one need to purchase them separately?

I've searched and read, but my eyes are bleary from info overload. Any help is appreciated. Thank you.

andypugh wrote:

I deleted the duplicate to keep the answers in one place

Thank you for that.

andypugh wrote:

I would suggest you start by sketching a block diagram of the existing machine, including each signal/power wire and what signal type it carries (on the analogue / digital / PWM level) Then figure out which bits are to be replaced, and that should give you a feel for what signal conversions are needed, and how many IO pins are involved.

And -

At its simplest, a wire (not counting power/gnd) You need 3 wires for an encoder (or 6 for a differential one), one for a limit switch or button, one for a PWM, one for a direction and so on.

This is part of the confusion on my part. Does a switch need one or two pins? Is one of them grounded to the machine frame, like in a chassis ground? Or, is it more conventional to run two wires for a switch? Are the two wires considered both part one I/O bit? Or is that two...? Another example - there's a pneumatic brake on the spindle. How many I/O spaces (bits?) <don't even know the vernacular yet> does that require? It's either off, or on, but is triggered through a solenoid valve. So, is that one or two? Spindle speed control? Again, pneumatic controlled, triggered from a solenoid valve that makes it's push air one way, or the other. One, two, or four I/O's? I've got the schematics for the machine, and the wires are fairly easy enough to trace out, but it's these little things I'm stumbling with. I want to understand what it would take to make the machine function exactly like it functions now. After that, I can worry about adding the capabilities that I want to.

andypugh wrote:

Both Mesa and Pico systems have opto-isolation built in to many of the cards. the standalone units you see for sale are to protect parallel ports. What they do is convert signal to light, shine that across the chip, and convert back to electrical signals. That means that there is no electrical connection between the circuits, so over-voltage can't get through. (It also allows the two sides of the circuit to work at different reference voltages)

Okay, thanks. I get that.

Thank you for the help!

andypugh wrote:

Just one, but you will need some interface electronics as an IO pin is 5V / a few mA, and the solenoid needs 24V (probably) and a few hundred mA. The Pico and Mesa hardware deals with this, though. As an example the Mesa 7i37 converts the 5V logic signals to 8 x 48V / 1A drivers. These can be viewed as switches, which can handle up to 48V and 1A, they don't actually output any voltage/current, so you would wire 24V to the solenoid valve, back to the high side of the driver, and then connect the low-side to the 24V GND. Logic 1 on the corrresponding IO bit of the Mesa FPGA card then switches the solenoid. I assume that the Pico cards work the same way.

Okay, so the 7i37 is basically interrupting the ground for the circuit? Am I understanding that correctly?


andypugh wrote:

Mesa cards have at leas 48 IO lines. The Pico system allows you to plug-in multiple 16-channel boards (and you can mount relays directly on the boards). You are unlikely to run out.

Okay, I think I am starting to get it...

Is there a common "standard" that most people seem to end up with? Like "this many" I/O's on average?
During my reading I have seen references to people having two 7i37's. Is this most common?

Jon was very helpful in getting an idea of what bits and baubles I would need/possibly desire to get from him and I need to write Peter to see what he would recommend too.

Thank you for the help. I am sure I will fall down again but I have a better idea now.

I have checked the links to examples of machines, but is anyone aware of any
good documented EMC conversions of already working Bridgeports? (besides Iggy's recent one)
Maybe a Mesa conversion for comparison?

Thank you.

heres one: machineability.com/Bridgeport_series_II.html