External Drivers

Sorry, but a Newbie question … I’m setting up a Smoothie with separate 5V & 12V PS, a third 24V PS for steppers driven from external drivers. The 3 PS GNDs are tied together, but NOT tied to the Smoothie … only the 5/12V + and - are tied to the Smoothieboard.
The External Drivers I have require EN, STP, DIR and +5V … not Ground
I connected the +5V directly from the PS (same %v PS supplying the Smoothie) … and the STP, EN & DIR as directed in the FAQ … but nothing.
I Tried Inverting the EN … still nothing (Voltage at the EN pin on the external stepper indicates 3.3V)
If I disconnect the EN the driver works … but is jerky, not smooth.
Same if I force the EN High with a pullup resistor from the +5V … but both of these options force the driver to be enables always.

  1. Is there any danger in keeping the driver always enabled?
  2. Could the jerky stepper driver indicate that the STP needs to be inverted as well?
  3. Should I run a separate GND so the external driver & Smoothie have the same GND? Should I tie the PS GNDs to the Smoothie (either a separate GND pin or the -5V)?

Thanks in advance

Imported from wikidot


  1. There should be no risk keeping it enabled
  2. It could indicate a thousand things, inverted STP is not a likely cause
  3. I’m not clear on what you call GND exactly, and why you make a distinction with " - ". You generally should have all GNDs tied together or you’ll get ground loops/com errors.

About your issue more generally ( « The External Drivers I have require EN, STP, DIR and +5V … not Ground » ), I think what you are looking for is “open-drain”
You connect end/step/dir to their proper inputs, then 5V to Smoothieboard’s 5V, and then you set each pin to be “open-drain” ( connects to GND instead of connecting to 3.3v ).

See bottom of http://smoothieware.org/configuring-smoothie