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Gertbot
Rev 2.3-September-2014
Alternative you can connect a switch which is normally closed and gets opened if the end-stop position is
reached. In that case you must program the end-stop as active high. This is the preferred way of
connecting an end-stop.
If you use end-stops you MUST make sure your motor’s rotational direction is correct. The simplest way
is to use the GUI and use the button of the GUI to make the motor move into the direction of end-stop A.
If the motor goes into the opposite direction swap your motor wires around or swap your end-stop wires
around. Also test your end-stop. There are two ways to do this:
1. Set the motor moving, operate the end-stop e.g. with a finger and check that the motor stops.
2. Operate the end-stop and check that the motor refuses to start in that direction
If it does not work blame your circuit, not the Gertbot as that has been thoroughly tested! Did you connect to the right 'ext' pin,
did you set the correct end-stop mode and polarity?
2.52.6 Connecting Open drain output
The Gertbot has two open drain ports. The switch element is an NMOSFET. Each can switch 30V 3A.
The following picture shows the open drain connections:
Gertbot open drain connections.
For those who are no familiar with open drain
connections: An open drain is like a switch. But you
can only switch DC currents and you must connect the
plus to the drain pin (because the switch is an
NMOSFETOD0 or OD1).
As you can see from the diagram above, there is no power available at the output. For an open drain
output to work, the user must provide an external power source. The open drain output does nothing
more than provide a path with a very low resistance to ground when it is switched on.
There is no protection on the open drain outputs. So the board will get damaged if you exceed the
current or voltage specification. MOSFETS have the notorious habit of a large capacitive coupling from
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