End-stops are small interrupters that you put at the end of each of your axes. When you boot your machine up, Smoothie has no way of knowing the position of each axis. When it starts a print, Smoothie moves the axis until it touches that interrupter, and when it is hit, it declares that that is position 0 for that axis. And does so for all axes.
This allows Smoothie to then precisely know where everything is relative to that initial position. It is quite convenient as it saves you the hassle of actually moving the machine into that position when you want to start a print. Automation is great.
However, end-stops are not necessary, you could do without them. They are just so convenient that most machines use them.
End-stops can also be used as Limit Switches which prevent the machine from attempting to move beyond the physical limits of the axis (by pausing/stopping movement when triggered), see the Endstops page for details about configuring Smoothie to use End Stops as limit switches.
This will concentrate on the most common type of end-stops : the mechanical ones. Other types exist like optical or hall-o sensors, see the dedicated appendixes for those.
TODO : Do those appendixes
There are plenty of fun and futuristic endstop types around : optical, laser, magnetic, force-sensitive, infrared, inductive, etc…
However, please note that the general feedback from the community, is that most of those are either less precise, less repeatable, or much more difficult to get to "work right", compared to the classical "mechanical" endstop.
The mechanical endstop is actually likely the most precise, repeatable and easy to get to work option you have at your disposal. Just because these other options exist and have been explored by the community, does not mean they are better.
You might happen have a good reason to use a fancy endstop, but if you don't, it's likely a good idea to stick with a mechanical one.
Mechanical end-stops are simple interrupters : when not pressed, they do not let the current pass, when pressed, they let the current pass. By connecting a digital input pin on the Smoothieboard to the interrupter, and connecting the other side of the interrupter to Ground, the Smoothieboard can read whether or not it is connected to Ground, and therefore whether or not the end-stop is pressed.
Most mechanical end-stops have 3 connection points, to which you have to attach your wires :
- C : Common
- NO : Normally Open, meaning it is not connected to C when the interrupter is not pressed, and connected to C when the interrupter is pressed.
- NC : Normally Closed, meaning it is connected to C when the interrupter is not pressed, and connected not to C when the interrupter is pressed.
Wiring a basic NC endstop
You want to connect the Signal ( green in the schematic ) and Ground ( blue in the schematic ) pins for the end-stop on the Smoothieboard, to the C and NC connection points on the end-stop.
For each endstop, we connect C to Signal and NC to Ground because this means the digital input pin ( endstop connector ) will be connected to Ground in it's normal state and cut from Ground when the button is pressed. This approach is less prone to noise than the reverse. See here for more information.
Another positive effect of this approach is, that if a wire breaks for some reason you get the same signal as if the endstop is pressed. That makes sure that even with a damaged wire you are not able to overrun the endstop.
Order is not important as polarity is not important here.
Make absolutely sure that you do not connect VCC ( red ) and GND ( blue ) to a mechanical (microswitch) endstop! Depending on your wiring that may fries your smoothieboard instantly or when the switch gets pressed. There is a wiring where this not happens and you switch the signal between VCC and GND, but if you're not careful enough you damage your board.
You want to connect your X end-stop to the X min pins, Y end-stop to the Y min pins, and Z end-stop to the Z min pins.
The default configuration most probably already has everything you need : the pins are already correct and the default speeds are reasonable.
Once they are wired, you can test your end-stops.
Now connect to your Smoothieboard over the serial interface. Power your machine on by plugging the PSU into the wall.
Now in Pronterface, home one axis by clicking the small "home" icon for that axis. Begin with X, then Y, then Z.
If your axis moves until it hits the end-stop, then stops when it hits it, moves a small distance back, then goes a bit slower back to the end-stop and stops, that end-stop is working fine.
On the other hand, if the axis moves a small distance in the wrong direction, then stops, you have a problem : your Smoothieboard always reads the end-stop as being pressed. So when you ask it to move until the end-stop is hit, it reads it immediately as pressed and stops there.
Another problem can be that the axis moves and never stops, even after the end-stop is physically hit. This means your Smoothieboard actually never reads the end-stop as being pressed.
There is a command that allows you to debug this kind of situation : in Pronterface, enter the "M119" G-code.
Smoothie will answer with the status of each endstop like this :
X min:1 Y min:0 Z min:0
This means : X endstop is pressed, Y and Z endstops are not pressed.
Use a combination of this command, and manually pressing end-stop, to determine what is going on.
If an end-stop is read as always pressed, or never pressed, even when you press or release it, then you probably have a wiring problem, check everything.
If an endstop is read as pressed when it is not, and not pressed when it is, then your end-stop is inverted.
You can fix that situation by inverting the digital input pin in your configuration file. For example if your X min endstop pin is inverted, change :
Here is the exact mapping of pin names to inputs on the Smoothieboard :
|Endstop||X MIN||X MAX||Y MIN||Y MAX||Z MIN||Z MAX|
More information can be found here. http://smoothieware.org/endstops