[Shessek]

Hello Everybody,
I've built my machine few years back. recently I wanted to start using limit switches and z probe to streamline some positioning processes. I've tried almost every combination of shielded-twisted pair wires for the wiring of the switches, but still, I get random triggering of the input pins and its just impossible to work with the limit switches. I tried changing the debounce values with no improvement.
Did anyone here experienced never ending noise in the inputs? how can I find the source? how do you suggest to fight it?

Thanks,
Tom

[DonKes]

I put capacitors across my switches on mine. I matched the size to the resistors on my BOB. I don't remember the size, but I described it in a post on Benchtop Machines. There are other threads there.

Don

[Shessek]

Hi Don,
Thank for the reply. How do you mean that you put the capacitors across the switches?
Do you have the link or tags of the post in Benchtop Machines?

Thanks
Tom

[Jon.N.CNC]

When are you getting the false triggers? Does it happen with machine not moving and spindle off?

In theory if you were to connect a length of screened cable left open circuit other end, and the screen wire to ground, and you get a false trigger it's unlikely the wire has caused it.

[Shessek]

I get the false trigger with and without the machine moving or spindle on...

[Jon.N.CNC]

I get the false trigger with and without the machine moving or spindle on...

Sounds like it could be noise at the Bob itself, could be a faulty bob or noisy psu possibly? Mains filters can help, especially if you have lots of machinery running on same supply..

You running your switches nc or no? Nc connection is less susceptible to noise.

Recall having a similar issue getting caused by a short effectively making a ground loop.

[Shessek]

the power supply to the BOB is an independent 5v power supply. I tried to run NC and NO I had better success with NC but it had noise as well. I read something about using higher voltage logic but I struggle with the circuit to have 5v into the pins on the BOB.

[Jon.N.CNC]

the power supply to the BOB is an independent 5v power supply. I tried to run NC and NO I had better success with NC but it had noise as well. I read something about using higher voltage logic but I struggle with the circuit to have 5v into the pins on the BOB.

How confident are you the 5v supply is a clean supply? 5v pretty standard for laptop ps adapters which Usually produce a clean supply if you have one laying around you could try.

You could try running an optocoupler board close to the Bob. That would be easier.

My advice first would be to pull the Bob from the enclosure and run it on its own on a bench with a test switch.

[mactec54]

Shessek

First you have to fix the spindle wiring, if you are using a VFD then this is the main source of your noise, if you are using a router for a spindle then you will need to change the cable to a shielded cable, and be sure to use correct Grounding of that cable

[Al_The_Man]

Proper star ground system and bonding of the machine to this point that should have the service ground going to it.
There are many previous posts on the subject here.
http://www.cnczone.com/forums/phase-...se-issues.html
Al.

[Shessek]

Hello Al,
Thank you for the link (I tried finding that type of thread but couldn't find it in the haystack). I read though it and I assume that it's grounding problem. Now my machine is build around an MDF chassis. all the wiring to the motors and a trimmer spindle run through cable carries. My question is, by star ground point, you mean a point that lead to the ground wire (yellow) from the wall AC outlet? (in my country L=Brown, N=Blue, GND=Yellow). if it is that, do I need to connect all metal parts to that point? Is it simply a matter of a rail that connects to the ground? My trimmer spindle have only 2 wires to the outlet, how do I ground it?
I am sure I do not have good grounding practices, but I had no Idea about all that... the machine runs great without the limit switches so it wasn't an issue until now...

Thank you again,
Tom

[mactec54]

Hello Al,
Thank you for the link (I tried finding that type of thread but couldn't find it in the haystack). I read though it and I assume that it's grounding problem. Now my machine is build around an MDF chassis. all the wiring to the motors and a trimmer spindle run through cable carries. My question is, by star ground point, you mean a point that lead to the ground wire (yellow) from the wall AC outlet? (in my country L=Brown, N=Blue, GND=Yellow). if it is that, do I need to connect all metal parts to that point? Is it simply a matter of a rail that connects to the ground? My trimmer spindle have only 2 wires to the outlet, how do I ground it?
I am sure I do not have good grounding practices, but I had no Idea about all that... the machine runs great without the limit switches so it wasn't an issue until now...

Thank you again,
Tom

Yes that is what you have to do for your Grounding, connect all metal parts to that one point, with your router/trim router, you can attach a Ground wire to the Router Body, most replace the Cable with a 3 wire so to have a Ground wire connected inside the Router to the metal body parts, these routers produce a lot of noise

You need to have a metal electrical Box or a Metal plate that all your electronics drives Etc are mounted on this then is where you can have a Grounding point/stud, any shields then can be directly Grounded to this main metal Plate, using clamps around the shield cable, the photo is how to do a Star Ground point, your main input power Ground is also attached at this point

[A_Camera]

Hello Everybody,
I've built my machine few years back. recently I wanted to start using limit switches and z probe to streamline some positioning processes. I've tried almost every combination of shielded-twisted pair wires for the wiring of the switches, but still, I get random triggering of the input pins and its just impossible to work with the limit switches. I tried changing the debounce values with no improvement.
Did anyone here experienced never ending noise in the inputs? how can I find the source? how do you suggest to fight it?

Thanks,
Tom

Sounds like you have an open circuit problem. Probably there is no pull up resistor on the input or something is wrong with your parallel port or the BOB or you simply have a lose wire.

[DonKes]

Hi Don,
Thank for the reply. How do you mean that you put the capacitors across the switches?
Do you have the link or tags of the post in Benchtop Machines?

Thanks
Tom

My switch connections go through a Jbox. I connect the capacitors from the switch wire to ground.
See http://www.cnczone.com/forums/bencht...-shielded.html

don

[mactec54]

Shessek

A capacitor is not needed if your system is wired correctly, that is what they used to do years ago, when they could not solve problems with noise, this is just a patch for a problem that needs to be fixed

Your ungrounded spindle is where you should start, then your stepper motors, any shields need to be grounded at the source, like in the photos, you can use a copper saddle or whatever you can dream up, always keep your wires after the Shield Grounding as short as possible

You can get these parts from more than one source here is the best one
EMC Cable Clamps - EMI Shielding & Grounding Components | icotek

[Shessek]

Hi Guys,
Thank you for all the info! I was ready to give up on the switches.
Tomorrow I will start grounding the various parts of the machine. I really hope it will solve the problem. BTW the BOB with a switch wired away from the machine works just fine, as soon as I get close again the noise comes back. I assume it's just me not being cautious with the wiring up till now.

I will report when it's all done, and hopefully, in working order.

Thanks again for all the information.

Tom

[Al_The_Man]

The other thing to look at is power supply commons, BOB's etc, if some are isolated from earth ground it can cause a problem.
Al.

[A_Camera]

I put capacitors across my switches on mine. I matched the size to the resistors on my BOB. I don't remember the size, but I described it in a post on Benchtop Machines. There are other threads there.

Don

That is a totally wrong approach. If you have noise you should find the cause of the noise and eliminate it. By adding a capacitor across the switch you make an attempt in HIDING the cause of the problem, not solving it. Other than that, you are creating a delay circuit, which is TOTALLY wrong in limit switches. The point of a limit switch is that it should stop the machine as soon as it has been hit and the signal should NOT be delayed or debounced at all. Limit switches should be normally closed circuits, meaning that if you get a cable fault (broken limit switch cabling) your machine should stop automatically, even if the limit switch was not hit. This can be a case of a lose connection, for example, which should be fixed immediately. Vibrations may trip the limit switch if you have bad connection, and the RC circuit you introduced by adding a capacitor across the switch may prevent this to happen.

In short, if you NEED to add capacitors across switches to make your machine work then there is something wrong with your design.

[DonKes]

How many Electrical engineers in the crowd?

There is NO shame in putting good time constants in a system.

Perfection is the enemy of being Done.

Don
BSEE MSEE but not in circuits.

[mactec54]

How many Electrical engineers in the crowd?

There is NO shame in putting good time constants in a system.

Perfection is the enemy of being Done.

Don
BSEE MSEE but not in circuits.

A_Camera is correct, jumping a cap like this can only be used in an RD quick fix to try something out, it is never used as a permanent fix, it is only a band-aid

You need to fix the source of the noise as A_Camera has said, it's easy to do with correct wiring

You should be ashamed if you have those degrees, to even suggest some one use this method, as a fix