Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: 7654321 on January 16, 2011, 12:12:19 PM

Title: limits triggered randomly no display
Post by: 7654321 on January 16, 2011, 12:12:19 PM
Finally got the limit switches in Mach 3 to work correctly but now almost randomly all stops as its moving and limit switch error appears and cant reset until I go to settings manual limit reset.
I am wired in series going to gnd and pin 11. Could it be in the home settings. Cannot see anything.No display in Display Mode???
Title: Re: limits triggered randomly no display
Post by: HimyKabibble on January 16, 2011, 12:28:41 PM
Put a good, stiff pull-up resistor, like 220 ohms, between pin 11 and your +5V source.  Use only shielded cable, with the shields tied to your ground bus ONLY at the BOB.  NEVER connect the shield at the machine end.

Ray L.
Title: Re: limits triggered randomly no display
Post by: BluePinnacle on January 18, 2011, 07:15:23 AM
This is probably a more elegant way of doing it than mine, which was to use a series loop with limit switches in series with a relay coil and a 12v power supply, and the relay contacts (NO) across the pins, safely inside an enclosure. Leakage current dragging the pin voltage down is the problem, caused by damp, coolant and age, and either way will solve it. HK's solution is very quick though and should do the trick with least effort and expense :)

Edit: I had this problem, and loads of other people have had it too, perhaps the installation guide should address it from the start? It would only take a few lines.
Title: Re: limits triggered randomly no display
Post by: brtech on January 18, 2011, 01:28:35 PM
You can change the settings in Mach to ignore the noise.  It's in General config, debounce.  A setting of 1000 is often good.  The pullup resistor is a very good idea.  Do this first.

HiymeKabibble, I've worked on computer systems for 30 years and the shield ground on one end only has always been the way it's done.  These days, much to my surprise, they advise grounding both ends, and making sure all frame earths are tied together well.  It turns out that at the Ghz frequencies that we have noise problems with today, single ended shielding isn't effective, and tying frame grounds together so that you don't get any current through the shield when grounded on both ends gives better results.  I have to keep repeating this, or I will forget it myself.  It's so weird to change something as fundamental as this, but you know, a Ghz here and a GHz there, and pretty soon you are talking high frequency noise.  Ghz signals don't behave all that well with conventional wiring, so we shouldn't expect the noise to behave the same.