Wiring home and limit switches

[Lee Roberts]

Wiring limits and home switches can be handled in a multitude of ways.
But first you need to know what software you plan to use before deciding on a method. Typically limit switches have both normally open contacts (NO) and normally closed (NC) contacts. Depending on how you want to wire you can wire them in series or parallel with other switches.







For example, CNCpro utilizes one input pin for each axis. Commonly that one input pin is wired to two fixed switches, one for home and the other for limit. It could also be used with one switch that moves with the axis and either via ramps or mechanical triggers actuates at the travel ends. Home is defined by the software setup as to which direction the axis is traveling when the switch activates. When using stepper motors, there typically isn't a need for more than two switches per axis. Servo's on the other hand, may need two dedicated limit switches to protect from a open loop failure causing a run away servo.

MACH3 software is very versatile and can be configured in many different ways. A common way is to have a seperate home switch for each axis, and one pin to all of the limit switches wired in series utilizing the normally closed contacts.

Below is two methods of wiring limit, home and kill switches. By utilizing a series wiring of normally closed limit switches, when one switch opens it sends a signal to the computer to stop issuing step pulses to the axis drive motors. In parallel, you have to use normally open switches to sense a switch activation. The top drawing utilizes independent normally closed switches for a home for each of 3 axis and is more compatible with MACH3. The bottom is another method to do home switches.

Utilizing normally closed switches is more noise immune, and thus reduces the risk of false switch actuation. The other noise benefit from utilizing NC contacts is coupling noise back into circuits and wiring for step/direction motor controllers.