Safety precautions when wiring external stepper drivers?
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I'm considering buying a DUET WIFI for my next project. I will require extra stepper drivers beyond the 5 supported by the DUET WIFI, I know there are expansion boards such as the DUEX2 & DUEX5 but since I already have a few of these external stepper driver boards (picture) as well as A4988 drivers, wires and dupont connectors on hand I decided to make use of those.
Other than triplechecking that all connections are how they should be, are there any extra safety precautions I should be taking to prevent damaging the board going this route? For example, it is possible that the steppers might rotate on their own when the machine is powered down (it might just be gravity moving them), should I be adding diodes between a driver and a stepper?
The main thing to make sure of is that the connection between the ground side of the Duet VIN terminal block and the ground side of the VIN terminal block on that board is short and secure. If it is too long then noise on the ground wire could cause the stepper driver to malfunction. If the ground wire is not secure than that board could feed VIN into the step/dir/end signals or the +3.3V from the Duet and damage it.
This requirement is not specific to the Duet, it applies to connecting non-isolated expansion stepper drivers to any electronics.
The three red pins labelled V are probably all connected together on that board, in which case they should be connected to +3.3V from the expansion connector.