Anonymous Breakout With HB-415 Stepper Driver: Mismatch

Turns out that the anonymous parallel port breakout board isn’t compatible with an optoisolated stepper driver: each output has a 1 kΩ series resistor that limits the current well below the driver optocoupler’s expectations. The driver has an internal 300 Ω resistor on each input, too, which doesn’t help in this situation.

A detailed look at the resistors lined up in front of the connectors:

Anonymous parallel breakout board - series resistors

Anonymous parallel breakout board – series resistors

The breakout board would work fine with non-isolated drivers, like the Pololu breakout boards, so it’s not really at fault. The fact that there’s no doc anywhere to be found means you (well, I) couldn’t discover this without buying it first, but … I suppose it’ll come in handy for something.

One could short across the resistors, but I intended to use this board for the initial bringup and all that soldering defeats the purpose.

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  1. #1 by madbodger on 20-February-2013 - 08:43

    Is there a reasonable way to run the couplers on 24 volts or so? Then all that series resistance would give a reasonable LED current.

    • #2 by Ed on 20-February-2013 - 09:01

      Nope, because those resistors are in series with the PC’s parallel port; +24 VDC wouldn’t do the port any good at all. Besides, that big 24 VDC supply will be running the motors on the far side of the isolators.

      If I were using the Mesa setup, I’d have a hardened breakout board and wouldn’t be screwing around with consumer-grade junk that doesn’t expect isolators… [grin]

  2. #3 by Brent Crosby on 20-February-2013 - 10:50

    24 volts? Wimps. I have my engraver motion control running off 50v with the 2M542 drivere :)

    • #4 by Ed on 20-February-2013 - 14:50

      Granted… but I’m dealing with little bitty 17-size steppers, not anything with real inductance, so higher voltage won’t produce better results.

      That said, I want to do a much better job of watching the winding current this time around.