Need Help!- Which Breakout Board?

[MetalBlade]

Originally Posted by The Blight How about all the other I/Os on the bob? Might be a good idea to isolate those from the parallel port.

Yes that makes since if you are interfacing anything other then a stepper controller that doesn't have isolated inputs already, but not as the first components the weak signal sees as it enters the bob.

If Mach 3 had more support for USB chips made by http://www.ftdichip.com/ then USB would be easier to implement, and we wouldn't even have to worry about this type of problem in the first place.

[MetalBlade]

On another thought, there is no reason to have opto isolation before a relay either. I mean think about it, you already have isolation because the relay uses a small signal to charge a coil, which is isolated from the higher voltage by magnetism instead of light in opto isolation. So people who shell out extra for these boards that have opto isolation are really just throwing their money away on redundancy.

[HimyKabibble]

Originally Posted by MetalBlade There is really no need for opto isolation of the bob if you're using geckos. The geckos already have isolated inputs. All you're doing is just adding to the total slew rate of the components on the bob and increasing the "time of flight" for the signal from the PC to the stepper controller. Just can't be good if you're going for higher rpm. As soon as I finish my breakout board, I plan to make a youtube video proving that all this crap added to the input of the bob, plus incorrect gluing of the logic families TTL and CMOS is the cause of "bad bob behavior". Hey that rhymes. There is no reason a properly designed board shouldn't be able to interface with a laptop without sinking too much current, pulling down the voltage, and causing missed steppes which makes the stepper motors stall out.

There IS a reason to have opto-isolation on all the OTHER inputs and outputs, like limit/home switches, motor controls, E-stop buttons, etc., etc. Also, there is no reason whatsoever a properly designed opto-isolation circuit should in any way impact the operation of the machine, even when driving Geckos. It is entirely possible to design opto-isolators that will run much faster than any machine will require, with low-enough signal skew as to be irrelevent. The problem is it seems many BOBs are NOT well designed, and mangle the signals. This is NOT a problem with opto-isolation in general, but simply a problem with those specific BOBs. My BOB is a perfect example. As I received it, it completely filtered out the step signals above about 40kHz. By simply re-biasing the optos, it is now quite happy at 250kHz. Few machines will ever need to go that fast. And, it is driving my G320s just fine at those speeds, despite the double opto-isolation. I'm also absolutely certain I could make it go at least 2X faster, probably faster, if I ever needed to.

Regards,
Ray L.

[MetalBlade]

Originally Posted by HimyKabibble There IS a reason to have opto-isolation on all the OTHER inputs and outputs, like limit/home switches, motor controls, E-stop buttons, etc., etc.

So you're worried about a little 5V signal from a switch messing up your computer? Interesting. I would think most people aren't using their brand new top of the line computers that they just bought for their milling work anyway, so all this talk about how it's going to destroy your computer is pointless when used computers are practically through away these days.

[HimyKabibble]

Originally Posted by MetalBlade So you're worried about a little 5V signal from a switch messing up your computer? Interesting. I would think most people aren't using their brand new top of the line computers that they just bought for their milling work anyway, so all this talk about how it's going to destroy your computer is pointless when used computers are practically through away these days.

First of all, many of us do not use 5V for switches. We use 12-24V, for better noise immunity. This is *necessary* and common practice on large machines (mine is a 9x49 knee mill). Not everyione here is running a little benchtop machine. Second, my computer, which I paid $100 for, is a 6 month old HP 3.6GHz pentium. And, no, I don't want it blown up, because I can't get another one at that price. Relay drivers are a *perfect* place for optos, because if the coil driver transistor fails, the relay can inject a voltage spike into the BOB, which could possibly propogate back to the PC. I'd much rather be able to replace a socketed 50 cent chip on my BOB, than have to buy a new $150 SmoothStepper or find another PC.

You could also have an accidental short in your motor drivers or power supply that ties your 5V bus to your 70V motor supply - S**t happens. Or short an AC line to a signal line. Anything like that will wipe out pretty much anything in it's path, up to the optos. Your PC will be spared. The whole idea is to protect against unplanned events, which DO occur, at least to the rest of us.

Opto isolation is insurance. Most people will never need it, but if you do, it's really nice to have it there. For me, it's a good trade-off. For you, perhaps not, but that's no reason to dismiss the entire concept. It's VERY widely used in industrial machines, and for good reason.

Regards,
Ray L.

[MetalBlade]

Originally Posted by HimyKabibble Opto isolation is insurance. Most people will never need it Regards, Ray L.

Do you worry a lot?

[MetalBlade]

Originally Posted by HimyKabibble First of all, many of us do not use 5V for switches. We use 12-24V, for better noise immunity. This is *necessary* and common practice on large machines (mine is a 9x49 knee mill). Not everyione here is running a little benchtop machine. Second, my computer, which I paid $100 for, is a 6 month old HP 3.6GHz pentium. And, no, I don't want it blown up, because I can't get another one at that price. Relay drivers are a *perfect* place for optos, because if the coil driver transistor fails, the relay can inject a voltage spike into the BOB, which could possibly propogate back to the PC. I'd much rather be able to replace a socketed 50 cent chip on my BOB, than have to buy a new $150 SmoothStepper or find another PC. You could also have an accidental short in your motor drivers or power supply that ties your 5V bus to your 70V motor supply - S**t happens. Or short an AC line to a signal line. Anything like that will wipe out pretty much anything in it's path, up to the optos. Your PC will be spared. The whole idea is to protect against unplanned events, which DO occur, at least to the rest of us. Opto isolation is insurance. Most people will never need it, but if you do, it's really nice to have it there. For me, it's a good trade-off. For you, perhaps not, but that's no reason to dismiss the entire concept. It's VERY widely used in industrial machines, and for good reason. Regards, Ray L.

So, what is this magnificent break out board that you're using? Does it have an on board relay? What voltages are required for its operation? If it has an on board rely, what voltage/current does the relay’s coil require?

[Torchhead]

Step & Dir into the Geckos are isolated with high speed (2 mhz) optos. (except for the 250 series). The buffering on a BOB is to improve the noise immunity of the parallel port. The outputs of a PP are logic level MOS. The pins are not designed to source over a few mills or sink more than about 10ma. The challenge of moving signals across cables over distance is that the higher the driving impedance the better antenna it makes. If you give some attention to proper design and buffer the step & dir signals you can clean them up, logic shift to full 5 V and provide a low impedance drive that will allow the use of 5 meter cables with no problems. The world of industrial electronics is a lot more challenging than logic control. Running logic level signals mixed in with high current PWM and other sources of EMI requires an understanding of grounding, isolation. shielding and differential signaling techniques that honestly baffles even some Electrical Enginners.

The opto isolation of inputs breaks ground loops, conducted noise and potentially destructive voltages. To be truly isolated the two circuits must NOT share the same ground (E.g. separate Power Supplies with separate common (grounds).

Inputs can typically be a lot slower than is needed for the step & dir signals.

All of our cards from day one have had full buffering on all step & dir, Double buffering on relay outputs and opto isolation on all inputs. We have always offered a dual power supply to drive the cards to give the isolated input power.

You can get by with ignoring the rules on smaller systems or where three is only one machine in the mix and distances are short. Toss in something like plamsa cutting or other machines and the gremlins of EMI and RFI will make you pay.

Maybe some other motor drives with straight TTL inputs need external isolation but it needs to be the right kind. Conventional optos have poor bandwidth. High speed optos are readily available but $$ compared to lower speed.

Proper documentation is always important. You should not have to take night courses in electronics to build a CNC machine!

TOM CAUDLE
www.CandCNC.com
Totally Modular CNC Electronics

Universal Breakout Board manual at www.CandCNC.com/PDF/UBOB_Manual.pdf

[MetalBlade]

Originally Posted by Torchhead Step & Dir into the Geckos are isolated with high speed (2 mhz) optos. (except for the 250 series). The buffering on a BOB is to improve the noise immunity of the parallel port. The outputs of a PP are logic level MOS. The pins are not designed to source over a few mills or sink more than about 10ma. The challenge of moving signals across cables over distance is that the higher the driving impedance the better antenna it makes. If you give some attention to proper design and buffer the step & dir signals you can clean them up, logic shift to full 5 V and provide a low impedance drive that will allow the use of 5 meter cables with no problems. The world of industrial electronics is a lot more challenging than logic control. Running logic level signals mixed in with high current PWM and other sources of EMI requires an understanding of grounding, isolation. shielding and differential signaling techniques that honestly baffles even some Electrical Enginners. The opto isolation of inputs breaks ground loops, conducted noise and potentially destructive voltages. To be truly isolated the two circuits must NOT share the same ground (E.g. separate Power Supplies with separate common (grounds). Inputs can typically be a lot slower than is needed for the step & dir signals. All of our cards from day one have had full buffering on all step & dir, Double buffering on relay outputs and opto isolation on all inputs. We have always offered a dual power supply to drive the cards to give the isolated input power. You can get by with ignoring the rules on smaller systems or where three is only one machine in the mix and distances are short. Toss in something like plamsa cutting or other machines and the gremlins of EMI and RFI will make you pay. Maybe some other motor drives with straight TTL inputs need external isolation but it needs to be the right kind. Conventional optos have poor bandwidth. High speed optos are readily available but $$ compared to lower speed. Proper documentation is always important. You should not have to take night courses in electronics to build a CNC machine! TOM CAUDLE www.CandCNC.com Totally Modular CNC Electronics Universal Breakout Board manual at www.CandCNC.com/PDF/UBOB_Manual.pdf

Wow, great response to the thread. Well, I'll concede that any person deciding on their breakout board, should consider environment, cost of quality components, and considerations for EMI/RFI.

I'll change my opinion to simple hobby CNC mills like the X3 don't need any more isolation other then which is provided by the geckos and relays. As Torchhead points out, good isolation does have it’s place though.

[Al_The_Man]

I always get a kick out of this search for super isolation.
I developed a personal strategy many years ago that although in the use of isolation components such as SSR and interfaces such as OPTO offer, I still referenced all the different systems to Earth ground, which essentially ends up at some point, to each other, including the PC power supply.
Looking through my records, I first started installing PC based systems in the late 1980's.
This has been in some the harshest industrial environments imaginable. These systems are still successfully in operation today.
Also I did not succumb to the credo that 'You must use a Industrial PC', I figured for $8,000 I could get alot of metalwork done.
The answer to the question on whether to isolate or not is personal preference, but the bottom line is, either method has to be done with due diligence.
I believe that many of the sellers of BOB's, stress the isolation method as it may be easier for many of those that use their product, may not have a background or experience to implement a uni-potential bonding system.
Some of the regular complaints of spurious switch trips etc, I swear are due to not adopting the common ground method.
Al.