Need some help with noise on Home and Limit switches for CNC

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I have converted an old NC mill to full CNC by adding a quill drive. I am using gecko drivers and an 72VDC power supply. I am having a problem with the home and limit switch wires picking up noise, i can't put a wire any longer than about 6 inches even if i connect that wire directly to 5VDC.

http://www.youtube.com/watch?v=G...

I have the breakout board jumpered to use pullups.
I do not have any problems with any of the drives
all work perfectly at 120 IPM and the geckos send 10,000 pulses per inch.

There are three home inputs. Initially I thought the pullup from the breakout board would be enough but when I add a wire and leave the other side unconnected it is triggering the switch with a low signal, sometimes you can see the led light up on the mach3 screen so I know it's noise. Two of the motors are 7AMPS and one is a 3amp.

I was able to get it to work by adding a bypass capacitor ( .10 UF) at the input line to the breakout board.
The switches will pull the line to ground through a 2n7000 mosfet. So the wire will be free floating at the switch side perhaps that needs a pullup as well? Wires will be 8 feet maximum. Using 18ga 5 wire shielded alarm system wire.

What suggestions to you have for capacitor size or other filtering methods to look at.

My first CNC I used a totally separate mega48 to read the signals from the home and limit switches (9 of them) and feed one short wire to the gecko driver.

1/2 inch aluminum plate is grounded from the AC line plug.

I ran a ground from the breakout board to the AC ground line as well. The 5VDC power supply is a wall wart that powers the breakout board.

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Start with the breakout board looks like a C10 model.
They have 4.7 Kilohm pull ups.

The card will allow you to either pull up or pulldown via these respirators.

There are about 10 of these resistors on the card.

What are You using for homing /end of travel switches?

If Your switches can handle say 10 milliamp, then replace the 4.7K resistors with 470 ohm resistors. That will quieten the BOB.

I am faced with a similar issue on a friends machine.

EDIT: make sure You are changing the resistors on the INPUT pins only.

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You can also get a lot of good help from cnczone.com there was pretty active participation when I used to visit it. Haven't been there in a while though.

Roger

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Thank's polecat. I forgot to mention I did put a 2k resistor from the boards 5VDC to the Z home pin (using pin 12 for Z home you can see it in the picture)

That helped a little but the capacitor really seemed to fix it. Since I do have a digital scope That's my project for tonight (after I watch Spartacus that is.) I will post snapshot of the noise.

Yes My switches will take 400MA (using 2n7000 fets) so a much smaller resistor i will try. I don't think I have to re solder the resistors on the board, i can just add a resistor connected to 5vdc so it would be 4.7K in parallel with say 470ohm.

My wall wart is 700MA and i don't have a schematic for the board )bought it about 4 or 8 years ago I think, I will have to Google to see what it uses for power, like I said though no trouble with the board connecting the computer to the drivers so it must be ok.

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What do you mean by your switches are 2n7000 fets?
What is driving these fets ?
show the schematic?

You can use dry contact switches directly no need for a buffer.