I'm having an issue with one of my limit switches tripping while running jobs. Is there some way to tell which limit switch is tripping? There doesn't seem to be any indication about which one is tripping, just that one has. BlackBox MCS OpenBuilds CONTROL 1.0.182 OpenBuilds micro limit switches I've tried troubleshooting this by disconnecting individual limit switches, but the issue is infrequent enough that I haven't been able to determine which one it is. I've tried connecting a multimeter to each limit switch and tapping on them and wiggling the wires, but I can't cause one of these limit switches to trip in this manner. Thanks
It might not be your switches - their leads make a nice aerial and can pick up EMI from mains cables especially. Are you using normally open or normally closed switches? Alex.
Normally open. I guess I can't rule out my routers power cord as a source of interference on the X axis. It's within about 2 inches of the limit switch. I'll try rerouting that. Otherwise, all my wiring is shielded and I don't see any other situations where the limit switches are close enough to anything else to pick up interference. Thanks Alex!
Just a thought. Normally Open switches are more susceptible to EMI than Normally Closed. I don't know enough about the blackbox to know whether it has interference suppression capacitors built in - @Peter Van Der Walt is probably the best person to answer that. If it hasn't 0.1 micro F capacitors across the signal and ground leads (at the controller end) might help - if EMI is the problem. Alex.
BlackBox has 10k pullups between the diode and MCU, reverse biased diode on input (does all kinds of miracles) and 0.1uF caps too, refer to the Schematic. NormallyOpen works just fine (and is the default setting in Grbl too so no need to fuss with software) even near my cheap chinese 40A air plasma with couple kilovolt HF start (HF trips up everything nearby, but not the blackbox) Paired with our accompanying Xtension Limit Switch you shouldnt be seeing any issues: (these step things up one more notch. Normally Open, but with even extra filtering and indicator LED to help with troubleshooting
Ok that seems easy enough. Thanks guys. It would be nice to know if this is built into the BlackBox though. Hopefully Peter will chime in on that.
As popular as EMI is to be blamed as the cause (and seperating high voltage / stepper cabling from low voltage cables is still a good idea) dont forget cheap switchea can also trigger from vibrations (;
Already did check above Pdf schematic of BlackBox is on files and drawings tab of its Build page too BlackBox
I don't have the Xtension limit switches, just the normal micro limit switches. Sounds like it's highly unlikely that this is EMI. I guess back to my original question, is there any way I can at least get the BlackBox to tell me which limit switch caused the stoppage?
Grbl cannot tell you which one. Best just to setup all 3 properly and clean up wire routing. Or just use them for homing, and turn off hard limits
No ours are pretty OK, just mentioning, one tends to think EMI and run with it, before thinking of simple issues like a bad solder joint, switch itself, wiring that can short while moving... Just made that as a point to not get overlooked
I'll definitely reassess my wiring situation and see how it goes. Are you saying set $21 to disabled and the homing function will still work? That seems like a reasonable workaround in the interim. Much better than what I have been doing, which is unplugging them...
Yes, homing and hard limits can be activated seperately. Soft limits require homing to be enabled if you intend using that Refer to github.com/gnea/grbl/wiki (a lot to read for sure, but all worth it)
I cannot find the circuit for the Xtension switch but since the page says that the LED comes on when the switch is triggered then that means the LED and resistor are connected from +V to the switched pin (and it has more filtering too) This means it effectively has a ~220 ohm pullup resistor. EMI will have a hard time pulling that down to trigger the input (-: This is nearly as good as the optocoupler suggested in the GRBL wiki.
I'm trying to diagnose my limit switches because I get a homing error. "Alarm 8 : Homing fail. Cycle failed to clear limit switch when pulling off. Try increasing pull-off setting or check wiring.". I'm not entirely sure how to read the troubleshooting leds. They're all red (saying on), and when I press them manually they turn to green (saying off). Is this how they're supposed to behave or are they "inverted" ?
I should mention that none of the switches are pressed when I get this error, which is why I'm thinking they might be inverted
Alarm 8: "Homing fail. Cycle failed to clear limit switch when pulling off. Try increasing pull-off setting or check wiring." - refer to gnea/grbl first, if your inversion setting does not match how the hardware is attached it won't work (or if you are unsure of that, you can also test $5=0, and $5=1 in turn one by one, making sure to reset in between changing and testing) Use the Troubleshooting tab in CONTROL to test Also check your steps-per-mm calibration - if it moves less than expected it will also fail to clear the switch on the return move. If its not inversion, also check gnea/grbl -> We recommend 10mm pull-off for most switches
Hi, thanks for the input. I'm already using the Troubleshooting tab in CONTROL to test, but I'm unsure what I'm supposed to see. Should the values read "on" or "off" when the switch is pressed?
Correct ON when the switch is pressed, OFF when its released. If it doesn't do that, its either wiring, or Grbl settings at play
That did it. The icons were showing it in reverse so I did the $5=1 , and now it works ! Thanks a bunch
