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I read how some of you have replaced the xcarve supplied wiring with a HomeDepot 22-2 shielded wire to prevent noise issues. I’m wiring up my xcarve tomorrow and would like to understand better the issues you have experienced.
I’m not quite clear on exactly what I need to do other than replace the limit switch wiring. I read you need to wire closed switches in series to the limit switch pins and change settings to normally close ($5=1) and activate hard limits. what is meant by g28 & g30? Are those sensors or just code?
Is there any better step-by-step info on this online? I watched Phil’s video but it didnt seem to explain anything about the wiring or switches.
Problems associated with electrical noise usually come up during the homing sequence. What happens is that the machine will start to do the homing cycle, but will stop prematurely due to a false trigger of one or more of the homing switches. Depending on the grbl options you select you can also see false triggering during a carving operation.
For some (like myself) shielded wires for the homing switches eliminate this type of problem. Others have experienced more severe noise issues and have had to take further action to eliminate false triggers.
One method for reducing the possibility of false triggers is to use normally closed switches and changing the $5 parameter as you posted. You don’t need additional switches unless you want to use hard limits.
I recommend that you just wire the shielded cable, use normally open switches, and do not use hard limits. If you have noise problems with that configuration you don’t have to change the wiring, but you may need to add some filtering at the place where the homing switch wires connect to the gShield.
I would recommend that you use homing with soft limits enabled which should be quite adequate.
G28 and G30 are g-code commands which tell grbl to move your machine to a specific location that you have programmed into grbl via the G28.1 and G30.1 commands. It is a convenient way to return to a known position. The position, once set, will be saved in EEPROM and will available even across a power down situation.
I don’t have an x carve but I do have a machine with limit switches. I wired mine with just regular 22 gauge wire and obviously had noise issues. People recommended that I get shielded cable, make some kind of noise cancelling circuit, all sorts of complicated solutions. What I ended up doing was just putting a .47uf capacitor across the input pins. It works perfectly now and I didn’t have to rewire everything or mess with complicated circuits. My advice would be to go that route if you haven’t already bought the shielded wire.
Using a 0.47uF capacitor is a noise cancelling circuit. As you have noted it’s not complicated.
The shielded wire is a slightly better solution, if it works, because the low pass filter (0.47uF cap) will reduce the response time on the switch. For the X-carve (or your machine) it might not be significant. If the noise problem persists with the shielded wire, then you can always go to the next step, which is a low pass filter.
Nice article EvanBruner. Reminds me of the days when I did this to solve car stereo noise problems. I’m curious as to why it wouldn’t be better to just eliminate the issue all together by simply using optical switches? Seems like the shielded wire and/or caps are just band-aids, when cutting the noise out of the loop would be more straight forward. Yes the optical switches would cost more than the caps, true, but for someone who is just starting out and hasn’t yet bought the mechanical switches, the optical switches would cost around the same as the mechanical switches and it would result in a much cleaner looking install. Just wondering…
Shielded wire is the eliminator. In many cases it prevents the noise from appearing on the signal wire, so you have effectively blocked the noise from happening.
Low pass filters for noise reduction are a bandaid, they work on the principal that a really quick pulse is noise and they filter it out. Component selection determines the length of the pulse to ignore.
I haven’t checked the response time or accuracy on proximity or hall effect sensors, but they certainly could be a good alternative.
I did check the mechanical switches for repeatability and have found that they can easily give 0.001 inch repeatability when homing the machine. This is sufficient for my use, so I haven’t pursued the alternatives.
I’ve had zero issues using the supplied twisted pair wiring. I think the only thing I’ve done really different is I used the drain wire on the motor wires and connected them to each stepper motor lug and then grounded the end near the grbl to the PSU case. I choose to do this because I work with large electro-mechanical systems (my day job) and grounding is always a first step in preventing home switch errors with our big machines. This is not the same as grounding at both ends (ground loop) because the x-carve chassis is not grounded, the only place it is grounded is the PSU.
To clarify how you connected the shield on the motor cables, are you, on both ends of each wire, connecting the drain wire to the ground wire in the motor cable?
Normally it’s a good safety feature for any machine/device, with exposed metal, to have that exposed metal hooked to earth ground when 120 volts is present in the device.
The green wire on the steppers wire (of the four) is not a ground, the steppers have Phase A, B coils, the frame of the stepper motor is the ground point, which IMO is neglected
I soldered the green wire extensions to the shielded “drain” wire for the steppers, wish I had a clearer pic.
Right! forgot about that, have not had any issue with the 611 making too much noise, i have the cable tied to the outside of the chain. Might want to run a ground just for that then, from the clamp to the electrical ground, but no issues so far. knock on wood
