Mechanical Endstop

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Overview

Mechanical switches are less complicated to implement and cheaper than optical endstops because they do not require a circuit board and only use 2 wires for connecting the switch. Pull up and down resistors can be put close to the main board. You can use contact switches and contact-less (usually magnetically actuated) mechanical switches. Contact-less magnetic switches are called reed switches. They are proximity switches that close (or switch over) if a magnet comes close enough (usually 1mm or less) and open if the magnet moves away. Reed switches are used as sensors in home alarm systems to detect open windows and doors.

How to wire a mechanical switch to replace an optical endstop.

Good reasons

  • The flags wont bend.
  • Cheaper.
    • No need for opto pcb.
    • Simple switches can be used on x and y axis.
    • You could even make your own contact switch from a few pieces of metal.
    • A simple way to put in max endstops.
  • You get to solder stuff.
  • Contactless (reed switch)

Bad reasons

  • Switches have a limited amount of on/off cycles. (Especially cheap ones).
  • Needs new way to mount switch, which will depend on the switch type.
  • The resolution and repeated function of the triggered distance is very critical on the z axis.
  • You have to solder stuff.

Opto Endstop v1.0, v2.1 and Tech Zone Remix

How to replace Opto Endstop v1.0, Opto Endstop v2.1 and Tech Zone Remix Endstop which share the same basic design.

Note the Tech Zone Remix Endstops are working the opposite way (normally closed) as the insctructions below, so you need to change either your firmware or the wiring of the switch to compensate.

Interface

Copied from DarwinOptoEndstop#Interface

Pin Function
+5 This is the pin to supply +5 volts on.
S This is the signal pin. It will output high (+5) if it is triggered, or low (0v) if it is clear
G This is the ground pin.


Switch requirements

You want a normally closed (NC) switch. Meaning you need a switch which connects two poles when not triggered. (A single pole double throw (SPDT) switch will work, if you wire up to the NC side of the switch -- ignore the NO pin). Read more at wikipedia.

"what happens if it's unplugged or my pet rabbit chews through the cable?" Design it such that when it's unplugged, it registers as "at the end" rather than "keep going". [1]

For the z axis, high resolution (aka short trigger distance) and high repeatability is needed.

The x and y axis resolution is not that important, unless you home the machine during a print. But you are of course encouraged to use a high quality switch if you can, as it certainly won't hurt.

Where to buy switches

Ebay

Ultimachine

Switch wiring

Mechanical endstop wiring.png

Eagle 5.10.0 light schematic: File:Mechanical endstop wiring schematic.sch

When the switch is off (like in the schematic above), it connects signal to ground. When the switch is triggered, the ground connection is cut and the signal is connected to 5v through the pull up resistor.

Make sure you keep the wires away from the motor leads and / or used screened cable as it is easy to pick up enough noise to get false triggering. [2]

Note: if you use Teacup Firmware, resistor R1 and the connection to 5V are obsolete. The ATmega has internal pullup resistors, which can be turned on with the USE_INTERNAL_PULLUPS flag. See config.h.dist, there.

Optional LED

If you want an indicator, you can hook up a LED (and a matching resistor).

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Generation 6 endstops

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Switch mounting

You need a way to mount the switch on the printer. Feel free to share your solutions and designs here. Modular design encouraged to fit different switches.

Mendel

X axis

The endstop holder from Prusa Mendel works fine. Take care to solder the wires pointing up, to place the holder as far out as possible, and this maximize the build space.

The way the wires are soldered here takes up a bit of space

Y axis

...

Z axis

Needs to sit very securely, but still be easy adjustable in small increments. The endstop holder from Prusa Mendel works fine.

Would probably be a good idea to attach the switch in two places

External links