Protecting My Mesa 7i76EU: Wiring Questions for Home Sensors and Touch Probe

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npostma
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23 May 2025 15:13 #328986 by npostma

Protecting My Mesa 7i76EU: Wiring Questions for Home Sensors and Touch Probe was created by npostma

Hi All,I’d like your input on my planned setup.
As I mentioned in my previous post, the latency on my new machine was so high that I had to switch from the parallel port to a Mesa card. Earlier this week, I received a Mesa 7i76EU board. It looks awesome—if a bit overwhelming at first glance!My plan:

Motors:
I’m using 3x Longs DM542A stepper drivers, which I plan to connect to Stepper 0/1/2 outputs on the Mesa board, using what I believe is called a “single-ended” wiring configuration. My plan is to connect +5V to the ENA+, DIR+, and STEP+ on each driver, and wire the ENA (5V), DIR-, and STEP- of each driver directly to the corresponding outputs on the Mesa card.
Spindle:
I have a Huanyang VFD 1.5KW for spindle control. For now, I’ll keep my Modbus-over-USB setup, which seems to work well enough. I’ve read that getting Modbus running directly on the Mesa board requires a bit more advanced configuration, so I’ll save that for later.
Homing Sensors (Capacitive, 3x):
My plan is to connect the +24V supply to the positive (brown) wire, and field ground to the negative (blue) wire of each sensor. I intend to connect the sensor output (black) wires to Input 1, 2, and 3 on the Mesa card.

Questions:

Current-limiting resistor for home sensors:
For the capacitive homing sensors, do I need to add a resistor between the output pin of the sensor and the Mesa input to protect against overcurrent? In the past, I’ve blown a few sensors and started using resistors to protect them, but those were cheap sensors—the Mesa card isn’t!
2-wire touch probe:
For my two-wire touch-off probe, I plan to connect one side to +24V field power and the signal wire to Input 4. Here too, should I add a resistor to avoid potential shorts or overcurrent situations?

Bonus questions:

Any recommendations for best practices when wiring sensors and stepper drivers to the Mesa 7i76EU?
Are there things I should definitely avoid to protect my Mesa card or improve reliability?
For those who have set up Modbus on the Mesa board, how steep is the learning curve compared to using Modbus over USB?

Thanks for your advice and experiences!

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PCW
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23 May 2025 15:28 #328989 by PCW

Replied by PCW on topic Protecting My Mesa 7i76EU: Wiring Questions for Home Sensors and Touch Probe

That looks basically OK

If you have PNP type sensors, you do not need any additional interface components
that is the sensor output goes directly to the 7I76EU input.

7I76XX inputs are quite rugged, they need no additional protection.

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npostma
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23 May 2025 15:34 #328990 by npostma

Replied by npostma on topic Protecting My Mesa 7i76EU: Wiring Questions for Home Sensors and Touch Probe

Thanks. Yes mine are of the PNP type. And same goes then for the input of the Touch sensor? This is not a PNP. This acts more like a mechanical switch.

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PCW
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23 May 2025 17:00 #328993 by PCW

Replied by PCW on topic Protecting My Mesa 7i76EU: Wiring Questions for Home Sensors and Touch Probe

Yes, the touch probe should be fine as long as it can be wired this way.

Note that many touch probes have a contact closure to ground, so be careful...

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npostma
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23 May 2025 18:18 - 23 May 2025 18:23 #328996 by npostma

Replied by npostma on topic Protecting My Mesa 7i76EU: Wiring Questions for Home Sensors and Touch Probe

Now i think of it, you're probably right. Maybe this is the case. What does imply for my setup / what should i look up so that i don't mess up the connection.

[EDIT]

I think i then have to connect it to GND and input right? (This is more safe, so i can test it first in this setup). I have this simple probe:

www.makerstore.com.au/wp-content/uploads...OOL-TP-V1-6a-NWM.png

Last edit: 23 May 2025 18:23 by npostma.

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andypugh
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23 May 2025 19:49 #329007 by andypugh

Replied by andypugh on topic Protecting My Mesa 7i76EU: Wiring Questions for Home Sensors and Touch Probe

One way to use a sinking input with a switch-to-ground sensor is to put a resitstor (I would probably try a 10k, choose something that can handle the current that flows when connected between 24V and gnd, anything over 2.5k @ 1/4 W size will be OK). Put one leg of the resistor in the 7i76 input, and connect the other to 24V, The connect the leg of the resistor that is in the input terminal to your switch-to-gnd.
With the switch closed the voltage at the input will be zero, with it open the resistor will pull-up the input and set it true in HAL.

You can invert the sense of the input in the HAL layer to get the right polarity,

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PCW
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23 May 2025 20:29 - 23 May 2025 20:30 #329015 by PCW

Replied by PCW on topic Protecting My Mesa 7i76EU: Wiring Questions for Home Sensors and Touch Probe

Yes, if the touch probe uses a contact to ground you can use a pull-up
resistor as Andy suggested.

For 7I76XX inputs this needs to be fairly stiff, say 2.2K 1/2W

This is because the 7I76XX input resistance is 11K and needs an input > 14.4V
for a high level at 24V Vfield, and a 10K resistor will not do this.

Last edit: 23 May 2025 20:30 by PCW.

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