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HBS86h alarm wiring

I have 4 HSB86 drivers with nema34 motors for my cnc router, how do i connect the alarm to the masso controller?

in the documentation i found the attached picture in the documentation.

But when i searched at this forum i found a topic where i read that you can connect the 24V to alarm + and from alarm - to an input on the masso.


I'm not totaly in to electronics and want to understand what is the reason/advantage of the resistor?

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The optocoupler transistor acts as a simple on/off switch. On its own the optocoupler does not provide a clean LOW (<1V) and HIGH (>3.5V) signals.

When the optocoupler is OFF the resistor "pulls up" the input to a HIGH state (for a 12V supply the input will see a voltage of approximately 6.5V).

When the optocoupler is ON it will provide a path of least resistance for the first x mA of current. In the case of the HBS86 the amount of current it can sink is 20mA. The maximum current that will pass through a 5.6K pull-up resistor is V/R = 24V / 5600 Ω = 0.0042A = 4.2 mA. As the "pull-up" current is smaller than the optocoupler sink rating the output transistor is considered "saturated" and the voltage drop will be about 0.6V.

Now for some grubby details on the Masso inputs: They are effectively LEDs connected to ground, therefore require about 3.1 V / 0.4 mA to turn on (Input 9 is a special case, it turns on >1.5V).

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Breezy has reacted to this post.


Thank you for this post and the diagrams.  Just rambling here now, I think I got it, Is this right?  Though I do not have the driver he posts what I do have is a opto coupler which is wired exactly like the drawing you show here in my system.  Now and If I understand what you are saying here,  and what my testing on the bench indicates is the signal for alarm from the driver turns on the control side of the Opto Coupler.

The output source is from ground. (pin 4) Thus the output to the Masso if hooked directly would also be a low signal on (pin 1 of Masso) Since pin 2 in Masso completes the circuit and is also ground there is no positive voltage present and no current flowing through the led in the Masso and no signal to the control.  In a normal system this input would be looking for a positive voltage to complete the circuit.

With your off example the current will be normally be flowing to the Masso and completing the circuit which will set the alarm in the system to always on and high unless there is a error in the drive.

I suppose this is where I get messed up and this is where the space bar change needs to happen on the input port in order to take the off position normal to low again so the alarm is out. I really don't have a handle on how that works internally in the Masso. I will just take there word for it.  What I do know I think is you have to have the positive source normal provided to the Masso instead of the negative source on the Masso terminal or it does not work.

Conversely in the Coupler ON position as you show it the current will flow away from the Masso when an alarm is issued and the Masso will go opposite or high setting the alarm.  All is well if the input has been switched from norm low to norm high.

So in other areas of this forum as the example above I have seen the 5.6 k resistor called out to power, but this is the first time I have seen the 6.8 in a circuit.  This all does now sorta seem to ring true.  Does it matter if your using 12 or 24 volt supplies and would that vary the resistor call outs.

Best regards,




Excellent diagram and explanation  @zombieengineer

@airnut Using the Spacebar does not change what is happening out on the MASSO input interfaces. It simply inverts the logic internally.
When the input goes High at the input terminal MASSO thinks it is Low if you have inverted the input and visa versa. Don't confuse actual electrical High and Low states with Logic High and Low states.

In the diagram the 6.8K resistor is shown after the Gray dot which means it is physically inside MASSO. It is what stops the Optocouple being destroyed when you connect 12 or 24 volts directly to an input.
Remember also that the MASSO input draws very little current so 5.6K works perfectly well for both 12 & 24 volt supplies and is a good all round value. There is no need to change its value depending on the supply voltage in this type of circuit.

Cheers Peter

Airnut has reacted to this post.


Well that is interesting.  I did not know about the grey dots as notations. Must have missed that lesson somewhere.  I was getting all set to add two resistors.  Of course I did not know a lot of things going into this project. Glad you guys are here.

In the spirit of learning,  Will you elaborate about the high and low logic thing. I am a little confused at this point. I was looking at it as being either a (0) low or + for high state voltage input to the device.  and what it was expecting to see. Does that not matter?

Thanks,  Steve

Hi Steve

Yes Logic absolutely matters. MASSO alarms when the input internal logic changes from Low to high.  ALWAYS
This is the logic that we are talking about and not what is actually happening out on the input.

In the electrical world 0 volts is logic low and above 3.5 volts is logic high but you have the ability to invert these before they become internal logic which is what you see on the F1 screen.

If we invert an input then 0 volts at the input shows internally as high and above 3.5V at the input shows internally as low then that is how MASSO will treat the input signal.
Think of the invert as a box that sits between the physical input the internal logic shown on the F1 screen. it will either let through what it sees on the input or invert it.

Cheers Peter

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The grey dots are meant to be screw terminals of the respective devices - it was the best I could do in 15 minutes at the time.


Breezy and Airnut have reacted to this post.

Peter,  Thank you.   I am going to restate this just to make sure I am on the right step here. So the inputs will accept at least 3.5 volts up to 24 volts and see that as high logic input signal and 0 volts for a low logic input.  All relative to the power supply hooked to the Masso.  Either 12 or 24 volts.

In order for the space bar invert to take effect in the system it must be attached to the input that is in this case high when not being activated by the driver and low when it is.  Masso makes this swap internally . Which is reversed as far as logic out of the driver is concerned.  Makes sense.  Thanks.

I guess I was struggling because my output was low and just using the space bar thing with out the input pulled high with a resistor just turned on and off the  F1 Red high signals and nothing happened except the machine locked up everything.

I fell off the wagon before we got to logic circuits in school and what is taken for granite by most is sometimes not clear. It is all starting to come together now. Much thanks.

Zombie,  I see it now,  All good,  Thanks.


Individual Axis alarms are all now working  great on my mill and I have a far better understanding of why and how all these systems and circuits work together.  I am constantly impressed with the features built into the Masso and how when I get the hook ups right the little things you don't think about when going into the build just all of a sudden are there and come alive.

I have been working on a better solution for interfacing the DG4S drives directly to Masso for several months now.  The interface card normally offered seams to be a band-aid and is not very elegant,  It has a bunch of extra connections you shouldn't need and does not have the capability to break out the individual axis alarms which the Masso supports. After building many different board designs and proto-types we have settled on a design and we do have a great solution that is plug and play with the Masso.  If you want to use the DG4S drives Please feel free to PM me if your interested.

Once again, Thanks Guys for all the information and assistance.  It makes a big difference.