View Full Version : Limits, homing, and relay switches

11-24-2003, 11:36 AM
I want to connect limit and homing switches, and eventually relays for shutting down and turning on the machine and other devices.

After much reading I still remain a bit confused by the numerous circuit options(resistors, filters, transistors, supply voltages, etc).
Is there a site that has the complete list of options (I heard there were about 50ways) for setting up a cnc machine for safety? And what about braking circuits to prevent inertia from creating a crash.
I've also heard that maybe limits aren't needed if care is taken monitoring the G-codes.

First, limits:
Do I wire a switch directly through the motor power circuit to break the motor power and stop further advance of that particular axis?


Is there a diagram (schematic) that I can read directly that provides the wiring and components needed from parallel port to switch that allows Mach2 to respond and stop the system from continuing once the limit switch is tripped(normally closed or open)?

I think I understand that a signal is generated when the switch is changed(high-low, low-high) and Mach2 detects this signal change and shuts off the motors to prevent a crash. Inertia and over-travel are other factors I believe for switch location.

Second, relays:

Here there is the option of solid state or elecro-mechanical. For the activation side, how does Mach2 supply the voltage to trigger the relay and thus completing the device power circuit. Do I need 12V activation relays using the 12V from the parallel port? Again, a schematic or drawing would suffice. I can figure the amps of the relays, but the actual circuit eludes me.

I'm using the Camtronics servo power supply with Gecko 320's.

I’m probably making this more difficult than it really is….

Just point in a good direction that will have waysides in case the fog gets too thick.


11-24-2003, 03:00 PM
additionally, What is the better relay type.....Solid state? Or mechanical.....and for what reasons.

11-24-2003, 04:54 PM
Download the Mach 2 manual from Art's site. Inside the manual you will find the correct method for connecting Limit and Home switches.

I use Mach 2 with both.

11-24-2003, 06:17 PM
I browsed through that manual before, but now I see I missed some details.