[Walky]

Hi

I'm having a hard time with my last cnc router. I just finished building it and just needed to wire the limit switches to the breakout box, which is optoisolated. Today I did just that and found myself in a horrible situation.

I think I'd better make a list of facts, so it's easier to know my situation:


- Input pins 10, 11, 12 and 13 are optoisolated.

- Input pin 15 is not optoisolated and is wired directly to que parallel port.

- The isolated and not isolated parts of the BOB have different grounds.

- With the steppers connected (doesn't matter if 1 or all 3), the isolated inputs have constant spikes that won't even let me move the steppers.

- With the steppers disconnected, the isolated inputs work fine.

- With the steppers connected, the non isolated input works perfectly if I connect a limit switch into it (the same switch that had spikes previously).

-I tried joining different grounds (not only the BOB's) in different ways to no avail, the problem is still there.

-If I join the grounds from the isolated and not isolated sides of the board, with a switch connected to the isolated side and another one connected to the non isolated side, the isolated one still have the same frequent spikes, while the non isolated one (which, as I previously said, usually works fine) starts having spikes, but not so frequently as the other switch.

-If I disconnect the USB plug (used only as a 5V supply to power the optoisolators), the interference stops and all the switches from the isolated side work perfectly, but I can't move the steppers correctly (they can move, but quite inconsistently since the optoisolators are not working with the proper 5V; curiously, they seem to be getting power from the DIR signals under this circumstances). In other worlds, the optoisolators seem to handle the limit switches fine when they aren't supposed to, but seem to be unable to do so under normal circumstances.

-If I use the BOB's integrated power regulator (an alternative to the usb power) I get the same spikes.

-All the switches I mentioned are installed in the machine and are wired near the steppers' cables side by side. They are all wired NC. I really, really don't want to replace the wiring since it took me a lot of time to finish it (it goes through holes and cable carriers), looks really clean, I'm very happy with the soldering job I did at the XLR connectors and I'm not even sure if that would fix the problem at all.

-If I wire an external switch to the isolated side, the spikes stop.




All those points make me think that there is probably some interference from the steppers' cables, but at a level that the parallel port can handle directly but the BOB's isolated side can't (the switches working when the optoisolators are not properly powered up makes things even weirder). I don't know if the optoisolators can't "copy" the signal accurately enough when the spikes are present, or if the problem lies in the BOB's way of handling ground.


I read someone suggested using 0.01uF capacitors parallel to each limit switch (between each input and ground) to filter the signal, I'll try that on monday if I still can't figure out what's going on by then.

The other option I can think of would be to build a relay board so I can drive the switches at 24V, but the 24V would be from the same psu I'm using to power the isolated side of the breakout board, would the interference would still be there?

This is my BOB:
http://www.probotix.com/manuals/PBX-RF_manual.pdf




Does anyone have any theory about what could be probably be happening?


I don't join all the switches and the e-stop to the only usable input since I would be left without hardware homing and touch probe. I don't want to use a "Y" parallel cable (or even a second parallel port) to feed the inputs directly, since the control box is really nice (made on my other CNC) with the limit's connector included in it and even "Limits/E-Stop" v-carved over it; it would just not look good after the 3 months I took designing and building this machine.

Thanks in advance!

[neilw20]

Take some photos so we can see exactly where your wiring, including power supply wire come and go to.

It is not sufficient just to connect grounds together, wherever they are.
This needs some planning, and what you have is symptomatic of some wrongly shared ground leads.

[Al_The_Man]

Is your PC power supply 5v common connected to ground? Usually this is done internally by ground buss screws.
By ground, I mean earth ground.
Using the term ground for various commons can get confusing.
If so I would take a Ground wire from PP common to the central earth ground plate.
Make sure the service ground is also connected to the central plate.
Also ensure that all metalic parts of the machine and motors are bonded back to the Earth Plate.
See this past post also http://www.cnczone.com/forums/showthread.php?t=71923
Al.

[Walky]

Is your PC power supply 5v common connected to ground? Usually this is done internally by ground buss screws.
By ground, I mean earth ground.
Using the term ground for various commons can get confusing.
If so I would take a Ground wire from PP common to the central earth ground plate.
Make sure the service ground is also connected to the central plate.
Also ensure that all metalic parts of the machine and motors are bonded back to the Earth Plate.
See this past post also http://www.cnczone.com/forums/showthread.php?t=71923
Al.

I checked the grounding and it seems fine (PP- 5Vgnd, PP-earth ground, 5Vgnd-earth ground). I noticed the BOB's PP case is not connected to the non-isolated side's ground; y tried connecting it to the isolated and non isolated grounds but it didn't make a difference. Maybe I should modify the BOB to bypass the opto and feed the inputs directly to the PP, but I don't want to screw up and kill the board, since I've already spent too much in this project.

The machine uses awg22 wire for the steppers and awg26 for the limit switches and e-stop, they run parallel all the way (the router is wired independently to make it easier to replace). I know I should have used shielded wire, but it was the only flexible wire I could find locally that could handle the motor's current (actually, I had to modify the XLR connectors to make the wires fit in it). The design makes it difficult to add extra wires (it would be way too tight) to ground the motors and metallic parts (luckily, most of the machine is made of MDF).

I'll try to add some pictures soon.

[Al_The_Man]

The design makes it difficult to add extra wires (it would be way too tight) to ground the motors and metallic parts (luckily, most of the machine is made of MDF).

I'll try to add some pictures soon.

Actually that is a case where it might be more important to add ground bonding, as with MDF, motor frames can become isolated from earth ground much easier.
Al.

[Walky]

Actually that is a case where it might be more important to add ground bonding, as with MDF, motor frames can become isolated from earth ground much easier.
Al.

Sorry, my mistake. I though of the metal structure as a big antenna and forgot it would be grounded.

BTW, I grounded the motors cases to the AC ground, and I'm still getting spikes :drowning:

It seems I'll probably have to replace the wiring (or try the relay board's approach). Would shielded 24awg be enough for my 6-wire (originally 8-wire) steppers at 41V, ~2.5A each?

Do you think there's a chance that it won't fix my problem?

[neilw20]

The wrong termination of ANY of the power wiring AND powers supply components can cause this fault.
As I said, take some pictures so we can assist.
Using a guessing game, has not much chance of resolving your problem.
A connecting wire as short as 1" in the wrong place, especially in the power supply low voltage terminations can cause this.

[Al_The_Man]

Unless I am missing something, I do not see a ground bus/star point set up?
There appears to be a neutral bus, but especially in the case of non-metallic enclosure and non-metallic machine construction, it is even more important, IMO.
The service ground and router frame ground, together with shields and bonding conductors should terminate at the Earth ground star point, whether or not you chose to opt for completely isolation between each part of the system is your call.
But Earth grounding and bonding applies whatever system is used.
My personal practice is well stated on previous record that I have always advocated bonding supplies and systems to earth ground, this also covers PC based controls, this has stood me in good stead for more decades than I care to remember, with no recollection of the problems you appear to be having.
Do NOT rely on picking up the earth ground for the PC and the router etc at their respective outlets, make sure they are bonded in the enclosure at the star point.
This may, or not be the cause of your problem, but this is where I would start, together with using shielded cable for some of those low level signals that appear to be strung around the machine.
Al.

[Walky]

Thanks, I'll get some shielded cable tomorrow.

I hope to have rewiring done by tuesday, I'll tell you the results as soon as I have this done. I'll ground as much as I can at the machine itself (rails, reinforcement threaded rods, etc).

[neilw20]

Thanks, I'll get some shielded cable tomorrow.

I hope to have rewiring done by tuesday, I'll tell you the results as soon as I have this done. I'll ground as much as I can at the machine itself (rails, reinforcement threaded rods, etc).

DON'T use the shield for a return or try to pass ANY current through the shield. It MUST be terminated to your ground star point, even by a long piece of wire.

Never try to 'save a wire' by using a wire connected to the same place.
It will work for light globes, but not with electronics.

[Walky]

Probotix suggested 0.1uF capacitors between ground and each input... I bought them today (and some shielded cable, just in case) and that did the trick!. :banana:

I even tried to induce interference and I didn't get any (mach3 is running right now just in case I get a spike). I'll solder the connectors again and see how it behaves; if I don't get a spike within the week I probably won't replace the wiring (as I said before, I'm in a hurry to finish this, and the machine design probably wouldn't allow for a quick replacement. Some microswitches are even glued in inaccesible places with heatshrink in every pin (easily breakable pins, btw).


You can't imagine how grateful I'm of all your help, be sure I'll apply all your advices in my next builds (and when I add limit switches to my other machine). I'll only use shielded cables from now on, and be sure that the first thing I'll do once I sell this router is a donation to the Zone (I'll do it right now if I could).

I'll make a topic about the finished machine very soon, be sure to check it out! Meanwhile I'll leave you a couple of videos from the last two weeks:

[nomedia="http://www.youtube.com/watch?v=jTzg1zJ0E_A"]YouTube- Fresadora CNC[/nomedia]
[nomedia="http://www.youtube.com/watch?v=GvpCh517_70"]YouTube- Tallado en pino.[/nomedia]

Thanks again! :cheers:

[sylvester1073]

Hi Walky,

1) Driver to stepper cables should be shielded and ground at one end.
2) Change Debounce settings to 2.

Regards Julian.

[Walky]

Hi Walky,

1) Driver to stepper cables should be shielded and ground at one end.
2) Change Debounce settings to 2.

Regards Julian.

Hi

I already fixed it by adding capacitors (parallel to each input). I won't use shielded cables this time because replacing all of it would be a problem at this point, but I will sure use them on every machine I build from now on. Debouncing didn't work for me before adding the capacitors, and luckily hasn't been neccesary after fixing the problem.

Thanks anyway for your will to help