we all need limits!

[senor J.]

I HAVE GECKO 320'S RUNNING MACH 2 I UNDERSTAND WHAT LIMIT AND HOMING SWITCHES ARE. I Need to know how to hook it up to the parallel port does it need its own power supply? I've never done this before please be specific in your response maybe detail the wiring involved in how your limit switches are set up on your machine if you have finished one, that would be a big help. I've searched the forum extensively on this subject and the answers to this question has always been answered vaugely.Thanks in advance

[turmite]

Hello senor J,
My best advice to you is to contact Robert Campbell at www.campbelldesigns.com/ and order one of the breakout boards that Jim Cullins makes for him. The board is designed specifically for the Mach2 and works great. It comes with good clear instructions and is easy to install.

Mike

[senor J.]

thanks turmite but I already have a breakout board I need to know how to wire the limit switches. Seems like it wouldn't be that hard??? anybody??

[turmite]

The limit pin #'s are in the pdf Mach2 manual available on line for artofcnc. Your breakout board should have instructions with it too. Is your board made specifically for Mach2? I think there is another one out there besides the Campbell. It's just that I have that particular board and know how easy it was to wire up.
Mike

[Graham S]

I think the board Mike refers to has terminals where the limit switches connect to.

The general answer is that you decide on which pin you want to use for a limit switch (depends what's left) add a pull up resister to the 5v (also on the port) and use the limit switch to pull the pin down to ground when it is switched.

Graham

[senor J.]

Ok Thanks graham. my breakout board consists of wires soldered directly to the pins. My limit switches are micro switches. SO if I understand you correctly I should be able to run the wire from the pin I want to use as the limit switch pin into the limit switch and then take the 5v pin, also from the printer port? and hook it to the limit switch with a pull up resister atached and that should work. If thats correct It should be REAL simple?
Thanks so much for your help

[DR-Motion]

senor J

You have two wires (connections) on your limit switch... a common and a normally open. Connect one wire to your designated limit input pin and the other to ground.
Next connect one end of your pullup resistor ( use anything from about 1K to 10K ) to 5 volts and the other end to your designated limit switch input pin.

Now with the switch in the normally open position, ( ie not in limit ) the input pin is seen at 5 volts ... and when the switch is closed, ( ie at the limit position ) the input is seen at ground. The pullup resistor limits the current from 5 to 0.5 mA depending on its value.

Hope this makes it clearer.

regards Gary

[Graham S]

Just to hammer the point home:

[arvidb]

Many limit switches also have a normally closed (N.C.) connection, in addition to the common and normally open (N.O.).

If you use the N.C. output of the switch, then the parallel port pin will see ground when the machine is not at a limit, and +5V when it is.

The advantage of connecting like this is that if a wire to the switch comes loose, then your machine will instantly halt with an overtravel condition, whereas it will simply not see the limit switch if you use the N.O. connection.

If you want to connect using the N.C. output, you use exactly the circuit desribed by Gary and Graham above, but connect to the N.C. output of your switch instead of the N.O., and set your controller program to active high input on the overtravel pin instead of active low.

Arvid

[Graham S]

Good point, I was just thinking electrically, the software doesn't mind as long as you define it but doing it like that is a great check automatically that at least the switches are connected.

I shall mod my picture

Graham

[chozo]

What's a recommended amp/voltage rating for a limit switch?

[jeffs555]

The limit switches are usually only switching 5 volts at less than 10ma, so just about any microswitch will do.