Help Mesa 7i37 and limit switchs

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28 Jul 2011 12:10 - 28 Jul 2011 13:15 #11948 by mataf01
Hello,
I would like to wire my limit switches to the 7i37 card of my mill
They are all NC switches, wired in serial, powered with 24V DC
Tell me if I'm right : I'll hook the positive wire of my power supply to the switches connected in serial, then to one of the input of the Mesa 7i37 ( which one?).
But what the heck will I do with the 24V Negatives cable, where do I Have to connect it??.
Do I have to put a resistor in the circuit to avoid sort circuits?
Thanks a lot for your help
Patrick
Last edit: 28 Jul 2011 13:15 by mataf01.

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28 Jul 2011 12:21 #11950 by btvpimill
I don't know anything about the MESA card, but I do know a little about switches. If they are connected in series, there should not be a bunch of 24V negatives.

you will go from +24V to 1 side of a switch, the other side will go to the next switch and so on until you run out of switches. then the last switch goes to the board input. Let me try this with ASCII art:

+24Vdc
o-/ -o
o-/ -o
o-/-o
MESA input

Ok clearly this is not my best talent, but o-/-o is a switch and
is wire

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28 Jul 2011 12:58 #11953 by andypugh
Do NOT connect the 24V to the 7i33. I don't think it has 24V-safe pins.

First you need to find out which pins on the 7i33 are not being used for a servo function. I assume that your config is set up with fewer than 4 encoders and PWMs. Running dmesg after emc2 has loaded (even after if it has quit again) will give you a list of all the FPGA board pins and their function in your config.

(I am not at all sure which pins are wired straight-through on the 7i33, and are available for GPIO, but the ENA lines seem likely.)

What sort of switches do you have that need 24V? Are these proximity switches? If so, I don't think you can wire them in series, you might need to take the logic output of each to a different GPIO pin.

If these are simply microswitches, then simply connect one end of the string of switches to the 7i33 input pin (which has a pull-up) and the other end to GND. If any switch is opened, the pull-up will bring the pin voltage high, and the logical value will go to 1 in HAL.

Do you have a link to the spec of these switches?

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28 Jul 2011 13:15 #11954 by mataf01
Thanks Andypugh
but I have made a mistake my card is a 7I37 NOT 7i33. Sorry about that, to much work and very tired at the moment (I've edited my post).
24 V because te command of all the relays of my mill are in 24V and I thought to use the same supply.
Thanks again
Patrick

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28 Jul 2011 13:22 #11956 by mataf01
Hello, btvpmimill
Tank you for your help
Patrick

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28 Jul 2011 14:04 #11959 by andypugh
mataf01 wrote:

Thanks Andypugh
but I have made a mistake my card is a 7I37 NOT 7i33.


Ah, that makes it simpler then. The 7i37 inputs are 24V-safe opto-couplers, they turn on when current flows from In+ to In- and off when it stops.

Connect +24V to the IN+ terminal of your selected channel.
Connect one side of the switch to the IN- side.
Connect the other side of your switch to the power supply 0V line.

I advocate having a separate switch set for each axis, then they can all home at the same time. A shared pin for all axes mandates that homing on one must be complete before the next can start.

If you need switches in series, then just wire as above, then 0V to switch one terminal 1, switch one to terminal 2 to switch two terminal 1, switch teo terminal two to switch three ternminal 1 ... ... ... switch N terminal 2 to IN-.

Be aware that. as far as I know, the firmware doesn't set the input/output nature of each pin when connected to a 7i37, so you need to have lines in the HAL file that define the pins correctly.

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28 Jul 2011 18:18 #11968 by mataf01
Hello andypugh
That's a fast and really well explained answer.
Thank's a lot.
Ps: I have my limit switches in serial and 3 other switches for homing ( one by axe)
Best regards
Patrick

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