homing problem- motors not backing up after switch is triggered

[mxpro32]

Hello, I'm having a problem with home switch setup in mach-3. I have my switches wired in series to one input pin (pin 11). My switches are operating correctly when I test them on the diagnostics page. The yellow light comes on when I press any of the switches. The problem is, when homing the z axis moves slowly up until the switch is triggered, but it doesn't back off the switch. It zeros the z axis dro, but the yellow light on the diagnostics page is still lit, and I get a warning message telling me that "one or more home switches is triggered, fix then home." Any ideas?

[DennisCNC]

You have the X, Y and Z home switches connected to one pin?
So when you push the X or Y switch the same light comes on, on the setting page?
If yes, how will Mach3 know what switch is activated. You need to have each axis limit switch go to a separate pin.

[Ferny]

I had the same exact problem intermittently on my rebuilt router. Upon homing the Z-axis would home and the direction LED would change but the motor would stop instantly...not backing off the switch. It turned out I had a lot of electrical noise (spikes larger than a logical high) on my series wired X-Y-Z-home switches. I put a 0.01uF 50V capacitor from that input line to ground on my parallel port breakout board to de-couple the noise and it solved my problem!

I also shortened my limit cable and ran it away from the motor and power cables hoping to help. If that doesn't help try holding the limit cable perpendicular (90 degrees) to each axis motor power cable, that is if it is a long enough cable. That might be hard to understand but hold it straight up and try it, then right and try it then left and try it...etc and see if there's a sweet spot where it works. Imagine the invisible electric field coming out of your motor cables perpendicular to them like a donut expanding and collapsing at your drive frequency! If your limit switch cable is parallel to the motor cable it is susceptible to picking up those chopping pulses! That can help test if it's motor noise causing a problem on the limit line.

p.s. all of my cables are unshielded but now it works like a champ.

Sorry for rambling!

Good Luck,

Ferny.

[Ferny]

Hey Guy's, My home limits are all connected in series to the same input. Just like the Mach3 tutorial explains. When you "Reference All Home" it does each axis 1 at a time first Z, then X, then Y. Mach3 knows when it hits a home switch and it is only moving 1 axis at a time that it's the correct switch. It works flawlessly for me.

Ferny.

[ger21]

You can try increasing the input debounce.

[mxpro32]

thanks guys. I think my problem is electrical noise/switch bounce because I discovered that once in a while, the motor will back off like it's supposed to. How do I increase the input debounce in mach? Also, I am using the pmdx breakout board with my switches connected between the input pin and ground. On the pmdx board, there are pull-up resistors that give a +5v signal whenever the normally closed switches are opened. So my settings are set to active high in mach-3. My question is, would I still connect the capacitor between the input and ground? Running the switch wires separately from my motor cables would be difficult because I am using cable carriers, so hopefully these two solutions will solve the problem. Thanks again.

[ger21]

How do I increase the input debounce in mach?

Top right corner of the General Config screen. Try 2000-3000 to start.

[Ferny]

If the switch de-bounce doesn't work try the cap.

Yes, put the cap from the input to ground. That will de-couple the noise to ground and not allow it into the B-O-B and computer. The good thing about cable carriers is they are nice and neat. On the flip side you have motor power and small signal cables laying side by side and they couple to each other. Any or all of these tips should take care of you.

When I looked at my input with a scope it had a ton of noise on it so I used a cap.

Good Luck,

Ferny

[ger21]

If the switch de-bounce doesn't work try the cap.

The cap would be prefereable, as the debounce is sort of a band aid. Using debounce is probably not as precise, since it adds a light delay to the switch being triggered.

[mxpro32]

well, I got the capacitor between the ground and the signal pin and now when I push the switches nothing happens. The yellow lights on the diagnostics page no longer light up. It's as if the capacitor is creating a short between the signal and the ground, which should be impossible because capacitors can't pass dc current. None the less, if i take the capacitor out the switches work again. I guess now I need to download the newest version of mach 3 because mine doesn't have a general config menu or a debounce setting as far as i can tell. Any ideas why the capacitor isn't working? I have it hooked to the breakout board between the ground and the signal pin exactly where the two wires of the switch series daisy chain hook into the breakout board. Is that correct?

[Eurisko]

Maybe this is what you need...



Please forgive the crude schematic, I used ImageFolio.

[ger21]

I guess now I need to download the newest version of mach 3 because mine doesn't have a general config menu or a debounce setting as far as i can tell.

How old is the version you have? Try Config Logic or Config State if it's an older version.